DISSERTATION
ON
RESIDENTIAL BUILDINGS ON SLOPING SITES
Submitted By: Deepa Sharma
Scholar Number: 101110047
Eighth Semester B. Arch.
Subject Coordinator: Prof. Manmohan Kapshe
DEPARTMENT OF ARCHITECTURE AND PLANNING
MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL
MAY 2014
I
MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY, BHOPAL
DEPARTMENT OF ARCHITECTURE AND PLANNING
DECLARATION
This dissertation, entitled RESIDENTIAL BUILDINGS ON SLOPING SITES is
being submitted in subject in ARC 426, Research Principles and Dissertation as part
of requirement for eighth semester of Bachelor of Architecture by the undersigned for
evaluation.
The matter embodied in this dissertation is either my own work or compilation of
others work, acknowledged properly. If, in future, it is found that the above statement
is false, then the institute may take any action against me as per rules.
Deepa Sharma
Scholar Number: 101110047
May 2014
II
ACKNOWLEDGEMENT
I would like to gratefully and sincerely thank Dr. Manmohan Kapshe for his
guidance, understanding, patience, and most importantly, his friendship during my
dissertation research study. He encouraged me to grow as an instructor and an
independent thinker. I am not sure many graduate students are given the opportunity
to develop their own individuality and self-sufficiency by being allowed to work with
such independence.
The writing of this dissertation has been one of the most significant academic
challenges I have ever taken. Though the following dissertation is an individual work,
I could never have reached the heights or explored the depths without the help of
books published by various authors, the e-books available on the internet, the research
papers published by various authors and the various organizations and websites
providing information related to my dissertation topic.
My very special thanks to my colleagues for their support and suggestions for my
research and all the other respective sources for helping me.
III
LIST OF CONTENTS
DECLARATION ....................................................................................................... I
ACKNOWLEDGEMENT ........................................................................................ II
LIST OF CONTENTS .............................................................................................. II
LIST OF FIGURES .................................................................................................. V
LIST OF TABLES ................................................................................................. VII
Chapter-1. INTRODUCTION ................................................................................... 1
1.1. Justification ..................................................................................................... 1
1.2. Need of the topic ............................................................................................. 2
1.3. Aim .................................................................................................................. 3
1.4. Objectives ........................................................................................................ 3
1.5. Scope ............................................................................................................... 4
1.6. Limitations ...................................................................................................... 5
1.7. Methodology ................................................................................................... 6
Chapter-2. UNDERSTANDING THE TOPOGRAPHY OF SLOPING
LANDFORMS AND DESIGN PRINCIPLES .............................................................. 8
2.1. Types of sloping landforms ............................................................................. 8
2.2. Buildings on slope: the implications and solutions ....................................... 11
2.3. Clustering of houses ...................................................................................... 16
2.4. Scenic opportunities ...................................................................................... 17
2.5. Conclusion ..................................................................................................... 18
Chapter-3. BUILDING TYPOLOGIES, CONSTRUCTION TECHNIQUES AND
SERVICES 19
3.1. Residential building typologies prevalent in North India ............................. 19
3.2. Residential building typologies prevalent in North East India ..................... 20
IV
3.3. Construction techniques to be adopted while designing the building in
sloping sites .............................................................................................................. 21
3.4. Roads: ............................................................................................................ 26
3.5. Practical considerations (landslide or slope stability) ................................... 32
3.6. Recommended practices ................................................................................ 35
3.7. Conclusion ..................................................................................................... 35
Chapter-4. LANDSCAPING ON SLOPING LANDFORMS ................................. 36
4.1. Planning a landscape on slope ....................................................................... 36
4.2. Landscaping principles on sloping sites ........................................................ 39
4.3. Ways of landscaping a sloping site ............................................................... 44
4.4. Erosion control for residential hillsides ........................................................ 48
4.5. Conclusion ..................................................................................................... 51
Chapter-5. CASE STUDIES OF DIFFERENT BUILDINGS ON SLOPING SITES
52
5.1. Car park house, Los Angeles......................................................................... 52
5.2. Family house, Prague .................................................................................... 53
5.3. Apartment block, North-East Italy ................................................................ 54
5.4. Stepped house, Spain..................................................................................... 56
5.5. Conclusion ..................................................................................................... 57
REFERENCES ........................................................................................................ 58
ANNEXURE............................................................................................................ 60
V
LIST OF FIGURES
Figure 2.1: Up slope (left) and Down slope (right) (Tweed Shire Council) ................. 9
Figure 2.2: Side slope (left) and Rolling slope (right) (Tweed Shire Council) .......... 10
Figure 2.3: Building on flat site (left) and moderate slope (right) (Tweed Shire
Council)........................................................................................................................ 11
Figure 2.4: Building on steep slope (left) and extreme slope (right) (Tweed Shire
Council)........................................................................................................................ 11
Figure 2.5: Design principles that must be taken care of (HRO) .............................. 15
Figure 2.6: Over excavation and creation of artificial plateau should be avoided
(North Tipperary County Council, 2009) .................................................................... 15
Figure 2.7: Step building design (Tweed Shire Council) ............................................ 16
Figure 2.8: Standard large lot residential layout, mixed single family layout with open
spaces, mixed density layout with open spaces ( from left to right) (City of Vernon-
Hillside Guidelines 2008, 2008) .................................................................................. 17
Figure 3.1: RC moment resisting frame with unreinforced masonry infill walls (left)
and open ground storey structure (right) (Assessment Project Group of IIT Bombay,
IIT Guwahati, IIT Kharagpur, IIT Madras, IIT Roorkee, 2013) .................................. 20
Figure 3.2: Cut and fill construction (left) and stilts construction (right)
Basements/Retaining walls (Tips for building on a sloped terrain, 2014) (How to
Build on a Sloping Site) ............................................................................................... 22
Figure 3.3: Basement construction on sloping sites (Tips for building on a sloped
terrain, 2014) ................................................................................................................ 23
Figure 3.4: Typical retaining wall construction, Gabion wall and rock buttress (from
left to right) (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME
ROADS BMPS) ........................................................................................................... 24
Figure 3.5: Common types of retaining structures (Slope Stabilization and Stability
of Cuts and Fills- LOW-VOLUME ROADS BMPS).................................................. 24
VI
Figure 3.6: Construction detail for retaining wall of height upto 2 m (left) and 5 m
(right) (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS
BMPS).......................................................................................................................... 25
Figure 3.7: Typical rock wall construction for smooth backfill (left) and face with
steps (right) (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME
ROADS BMPS) ........................................................................................................... 25
Figure 3.8: Two lane road (left) and split level access road (right) (California Coastal
Commission) ................................................................................................................ 27
Figure 3.9: Single lane road with pullouts (left) and bridge (right) (California Coastal
Commission) ................................................................................................................ 28
Figure 3.10: Culvert (left) and Arizona crossing (right) (California Coastal
Commission) ................................................................................................................ 29
Figure 3.11: Balanced cut and fill for most of the construction on hill slopes (Slope
Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS) ....... 30
Figure 3.12: Full bench cuts for slopes exceeding 60% (Slope Stabilization and
Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS) ................................... 30
Figure 3.13: Through cut (Slope Stabilization and Stability of Cuts and Fills- LOW-
VOLUME ROADS BMPS) ......................................................................................... 31
Figure 3.14: Typical fill (Slope Stabilization and Stability of Cuts and Fills- LOW-
VOLUME ROADS BMPS) ......................................................................................... 31
Figure 3.15: Benched slope fill with layer placement (Slope Stabilization and Stability
of Cuts and Fills- LOW-VOLUME ROADS BMPS).................................................. 31
Figure 3.16: Reinforced fill. These can be used as an alternative for retaining wall
(Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
...................................................................................................................................... 32
Figure 3.17: Through fill (Slope Stabilization and Stability of Cuts and Fills- LOW-
VOLUME ROADS BMPS) ......................................................................................... 32
Figure 3.18: Contour graded slope (left) and Steep geogrid slope (right) (California
Coastal Commission) ................................................................................................... 34
VII
Figure 4.1: Ground covers for steep slopes (Alders) .................................................. 42
Figure 4.2: Steep sidewalk grades are a significant barrier to access for many
pedestrians (left), If he side walk grade exceeds 5% level landings should be provide
at regular intervals (right) (Federal Highway Administration, Updated: 02/10/2014)
...................................................................................................................................... 44
Figure 4.3: Gardens showing terracing (Washburn) .................................................. 45
Figure 4.4: Construction of tiered garden (Alpha Landscapes Design ltd.) ............... 46
Figure 4.5: Rock landscaping (DIY network) .............................................................. 47
Figure 4.6: A sloping site, made up of semicircular layers. The key stone is the largest
stone. Subsequent stones get progressively shallower so that they disappear into the
ground at the sides of the site. (Rock Landscaping Ideas Flat and Sloping Sites) ... 48
Figure 5.1: Car park house built on sloping site (ArchInspire) .................................. 52
Figure 5.2: Conceptual sketches developed by the architect (Grido Architektura and
Design) ......................................................................................................................... 53
Figure 5.3: View of the house (top), timber frame construction (bottom left), sections
(bottom right) (Grido Architektura and Design) ......................................................... 54
Figure 5.4: The three-storey Dolomitenblick building (Plazma Studio) ..................... 55
Figure 5.5: Tiered home on sloping site in Spain (left), view showing arrangement of
spaces (right) (Eva Designs, 2014) .............................................................................. 56
Figure 5.6: Side view of home showing stepped appearance (Eva Designs, 2014) .... 56
LIST OF TABLES
Table 1 : Common stable slope ratios for varying soil/rock conditions (Slope
Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS) ....... 60
VIII
Table 2 : Relation between number of levels and number of gabions for flat backfill
(Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
...................................................................................................................................... 61
Table 3 : Relation between number of levels and number of gabions for face with
steps (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS
BMPS).......................................................................................................................... 61
1
CHAPTER-1. INTRODUCTION
The housing we build today will not only help to shape our environment in the
immediate future, it will also be determining the environmental quality of spaces. This
study describes the contributions to quality and sustainability of the design of new
residential developments on sloping sites.
The context given in the report is aimed at achieving attractive and functional places
through better design, better construction techniques and services, proper use of
building materials, suitability of landslopes for different buildings to promote:
1. The wider context of the local setting, the characteristics of the site for
development
2. More sustainable patterns of living and working
3. More effective integration between topography and built up
4. The creation of attractive places in which people are happy to live, work and
take their leisure.
5. Greater responsiveness to site and setting in the layout of new development to
achieve a better balance between requirements and other factors.
The creation of attractive residential environments with a genuine sense of place is a
prerequisite to achieving sustainability. The quality of where we live depends not just
on the design of buildings, but on their layout and landscaping, the arrangements
made for access, and in particular, how they relate to their surroundings. It is intended
to encourage the interconnection of design considerations of the setting, landscape
design, circulation patterns and buildings to form a coherent design structure.
1.1. Justification
In global context, each and every piece of land should be praised to its individuality.
At designing point of view, each site has got its own potential in terms of its richness,
fertility, texture, ability to bear, nearby features like deep valleys, water bodies,
hillocks, ridges and soaring mountains.
Designing of building on sloping sites while avoiding the cut and fill construction
techniques is cumbersome process because of change in ground levels. But spaces
should be carved out respecting the character and physical behavior of site, thus
2
achieving the better functional space. These techniques are only employed when
necessary.
Designing on sloping spaces is a move away from typical standards of flat sites to a
more integrated and functional approach to achieve high quality and sustainable
designs. Most of the sloping sites due to its beautiful and admiring surrounding
features, the user can enjoy the nature upto its full expanse.
Spaces designed in sloping sites may differs from those of in flat or less sloping sites
(where presence of contours can be neglected) in terms of their approach, dimensions,
geometry, proportions, views, etc. Those spaces may prove inconvenient or
exhaustive for physically challenged people, but that can also be avoided by following
some design criteria, thus making the space more functional and universal.
The execution principles, services utilized for construction of buildings are quite
different from those adopted in flat sites. Also the ambient climatic conditions reaches
extreme in most of the regions having uneven landforms. These places are also
vulnerable to other natural calamities like seismic activities, storms, snowfall, hail,
etc.
Some of the buildings are constructed using locally available materials and techniques
which may not be prevailing in other regions because there, the transport of building
materials proves laborious.
So, the study would help architects/ designers to get the complete idea of
perspective of spaces and designing according to the requirement of user and
exploring the site upto its full extent.
1.2. Need of the topic
1. To understand the way that how spaces should be carved out respecting the
site potential, field patterns, townscapes and landscapes.
2. To lessen the impact of seismic impacts, wind loads, and other dynamic
loadings on building and its surroundings.
3. To design spaces according to the extreme of climates
4. To minimize the cut and fill construction techniques, adopting sustainable and
green building principles as far as possible.
5. To make the space more functional for physically challenged people.
3
6. Development designed to emphasis a sense of place and community with
proper movement networks.
7. Move away from conventional standards to more interesting approach for
achieving high quality and functional spaces.
8. To enhance the importance of views and vistas.
9. Protection of existing trees and other important natural and topographical
features.
10. Considers the wider context of the local setting, the characteristics of the site
for development, and strategies for the overall design character of a proposal.
11. Giving guidance on the main elements needed to achieve high quality design,
from the overall landscape and urban design considerations to the layout of
dwellings, means of access and patterns of movement.
12. Integrate with existing patterns of movement.
1.3. Aim
The main purpose of the study is to contribute to the methodologies and principles
employed for carving out spaces in sloping sites. The study is also intended to
contribute to the better understanding of terrain and opportunities for creating spaces
which have greater responsiveness to site.
To establish design principles for different typologies of residential buildings on
sloping sites.
1.4. Objectives
Residential development on sloping sites must complement the scenic hillside
character by integrating unique or special natural features such as landforms, rock
outcroppings, viable existing stands of trees and vegetation, ravines, water features,
hilltops and ridgelines; protect wildlife habitat; avoid unstable or hazardous sites and
protect lives and property from hazardous conditions, such as rock falls, storm runoff,
erosion, etc.; provide safe year round access for residents, visitors and service
providers;
1. Suitability of land slopes for different buildings and design criteria
4
Sloping landforms can be classified on the basis of direction of slope and amount of
slope. Each site has its individuality on which a particular type of arrangement of
spaces can be done. This further requires analysis of some of the other parameters. A
thorough investigation and assessment of ground conditions and stability is essential
to determine whether a site is suitable for building on, where the best place may be to
locate a building and the type of structural system that will be required.
2. How sloping landforms can be best accomplished for getting functional and risk
free spaces
Sloping sites are generally prone to soil erosion, landslides, debris flow, seismic
activities, etc. These are also burdensome for physically challenged people. But
incorporating some of the design criteria, spaces can be made more functional and
risk free. Natural character of the hillside should be preserved as well as provide
scenic views from a hillside site.
3. Design principles, construction techniques, materials and services
Design solutions/construction techniques like step building design, cut/fill
construction techniques, raising the building on stilts/poles, retaining wall
construction, drainage issues, seepage problems should be incorporated which
respects the site potential upto its full expanse and lessen the impact of seismic
loading and other dynamic loadings.
4. Scope of landscaping on sloping sites
Landscapes on sloping sites will certainly take a little more thought and effort than for
a normal flat site but the results can be very interesting by playing with change in
levels, creating stepped appearance, terracing, tiering, etc. The biggest concern is
usually the risk of erosion. Additionally, planting and maintaining plants on inclines
can be a difficult undertaking. However, there are many ways to successfully
landscape a slope and create an attractive incline.
1.5. Scope
The study is intended for use in the design of all the proposals for residential
buildings of all typologies in global context having uneven terrains from small scale
housing projects to major housing projects on large sites satisfying the climatic
5
conditions, culture and heritage of the region and also respecting the landform.
Nevertheless, the principles in the report will be used by architects as a basis for
assessing any proposal.
The study also have emphasis on landscaping features(decks, patios, pavers, pergolas,
entryways, walkways, plants, retaining walls, lighting, water bodies, etc.), process of
landscaping in slopes, hardscaping and softscaping.
Preservation of slopes or hillside erosion control, importance of heights and
proportions, designing open spaces, protection of existing trees, and other important
natural and topographical features is also included in report.
Study also includes construction of houses using modern building materials and
techniques as well as vernacular materials and techniques.
The study also includes the construction technologies, materials, services (water
supply, sewage disposal, gas, electricity, lighting and telecommunication) and study
about vehicular and pedestrian networks.
Seismic vulnerability assessment of building types is also included in study.
Cost factors are not taken into consideration in this study.
The study also not includes designing in largely steep slopes, inaccessible sites, places
having frequent landslides, other natural calamities like heavy snowfall, hail storm,
etc.
The study also not includes the interior designing of the spaces and elements (wall
treatments, finishes, flooring, ceiling, etc.)
1.6. Limitations
The study will be helpful for architects and designers for proposals of all types of
residential buildings but not commercial, industrial, recreational buildings like
shopping malls, large office buildings, sports complexes and stadiums.
The study includes information about construction techniques and materials employed
for particular type of landform but not project management and construction
management of execution, materials, time taken for execution, labours and cost.
6
The scope of study could be very vast and very much extensive in nature involving all
constructional techniques and structural aspects. But, sighting the specific need and
the other constraints such as time etc., we should draw a limit to our area of
exploration. No live case studies are done because of time constraint.
1.7. Methodology
The study encompasses the information on topics from detailed research referring
journals, documents, literature reviews, case studies, in each and every objective of
the study.
Detailed analysis of the visual character of the local setting, topography, field patterns
(using topographical survey techniques), landmarks, historic features and nature
conservation interests is done to provide a source of inspiration for the design.
Maps and aerial photographs can provide useful indicators of visual character and
help to highlight the character of the local landscape or townscape.
Topographic survey is done to get the necessary data to produce a topographic map of
the earths surface. This map will include contour lines, location of natural features,
such as streams, gullies, and ditches and man-made features like bridges, culverts,
roads, fences, etc. which are needful for detailed planning. The best practical method
of presenting topography is by means of contour maps.
Analysis of the local landscape and townscape is important to help relate the
development more sensitively to its surroundings. Such analysis should include
patterns of landscape and townscape, spatial characteristics and building forms, and
the results should be illustrated on plan.
The analysis also includes the visual characteristics of building forms and related
elements, such as: aspect and orientation; proportion; the balance of solid to void; the
shapes and details of roofs, chimneys, windows and doors and the materials used.
7
Primary studies about the type of geography of different places in global context from various websites and its response to the building and
building's response to the site
Study about the behavior of building in particular type of landform through case studies and browsing illustrations of buildings in sloping sites to get the
perspective of spaces
Collection of information about different typologies of residential buildings and their design principles referring various journals and literature reviews
Study of construction techniques, services, circulation patterns, vulnerability assesment, scope
of landscaping from various literature reviews, journals, documents, videos and documentaries
Assimilation of information in proper hierarchy and preparation of report
reviews
Preparation of final report
8
CHAPTER-2. UNDERSTANDING THE TOPOGRAPHY OF
SLOPING LANDFORMS AND DESIGN PRINCIPLES
Hillsides are defined as lands in their natural state that have a slope angle of 12% or
greater for a minimum horizontal distance of 10 meters. Landforms may be extremely
sloped or almost flat. The steepness of slopes can also be described in degrees;
however, for the purpose of land development it is defined as either a percent or a
ratio.
Engineered structural slopes are required in all fill locations where roads, utilities or
buildings are being supported. These slopes can be as steep as 100%, or 1:1,
depending on materials used and compaction methods. The use of geotextiles as part
of a structurally engineered design can further increase the maximum slope attainable.
Typical engineered slopes are 67% or 1.5:1. 1.5:1 slopes, though they may be
structurally acceptable, are generally too steep to properly retain the minimum depth
of topsoil of 150mm necessary to enable re-growth of native plant species. Minimum
finished slopes that will consistently retain topsoil are 50% (2:1) or flatter. (Design
Ideas for sloping sites)
Sloping sites offer unique opportunities including great views, access to cooling
breezes and often result in more interesting building forms where the design
accommodates the slope. They do however require more design consideration than a
flat block to balance house design, excavation and potential amenity impacts on
neighboring properties. On a sloping site, off the shelf designs which have been
specifically designed for a flat block should be avoided to get interested spaces
incorporated in and to achieve greater responsiveness to site. Key importance of slope
development is the preservation of land which provides natural space, buffering and
habitat for native plants and animals. (Design Ideas for sloping sites)
2.1. Types of sloping landforms
There can be diverse types of landforms in sloping sites which are listed below based
on the direction and amount of slope which decides the type of spaces in residential
buildings.
(Tweed Shire Council)
9
2.1.1. Classification based on direction of slope of the site
Landslopes can be classified on the basis of direction of slope as Down slope, Up
slope, Side slope and Rolling slope
2.1.1.1. Up slope
1. Site rises up from road. (see Figure 2.1)
2. Generally require more cut allowing for lower level/garage.
3. Garage doors and driveways are generally more visually dominant from the
street on up slope lots. A projecting balcony over the garage reduces this
visual impact.
4. A level transition off the street level into the elevated living areas should be
aim at.
2.1.1.2. Down slope
1. Site falls away from road. (see Figure 2.1)
2. Garage carports are easier to build closer to the street.
3. An extra storey at the rear should be avoided which significantly increases the
buildings height and bulk from the rear.
Figure 2.1: Up slope (left) and Down slope (right) (Tweed Shire Council)
2.1.1.3. Side slope
1. Site rises/falls away from side boundaries. (see Figure 2.2)
2. House with the garage at lower level with living space above can be designed.
3. Site benching and large retaining walls at property boundaries which can
lead to overshadowing, overlooking and drainage issued should be avoided.
10
2.1.1.4. Rolling slope
1. Site rises/falls in two or more directions. (see Figure 2.2)
2. Level change within the building design by splitting the house over different
floor levels can be designed.
3. Unsightly retaining walls outside of the building envelope should be avoided.
Figure 2.2: Side slope (left) and Rolling slope (right) (Tweed Shire Council)
2.1.2. Classification based on direction of slope of the site
Landforms may be flat, having moderate slope, steep slope or extreme slope
depending upon the terrain which decides the construction techniques to be adopted
(whether single slab, post and beam construction or pole construction should be
employed)
2.1.2.1. Flat sites
Single slab on ground construction are only appropriate up to a slope incline of 4 or
7 as the cut/fill required becomes excessive (over 1.5m). Slopes between 4-6 should
accommodate some level change within the building footprint. (see Figure 2.3)
2.1.2.2. Moderate slope
On slopes of 6-12, single slab construction should be avoided (up to 1:5). Two or
more slabs or part slab/part post and beam construction techniques should be adopted.
(see Figure 2.3 )
11
2.1.2.3. Steep slope
On slopes over 12-18 (1:5-1:3) post and beam construction which steps with the
site. This may include a lower part level which may be a concrete slab. (see Figure
2.4)
2.1.2.4. Extreme slope
On slopes over 18 (1:3), suspended or pole construction is required. This degree of
slope is more suited to a downslope configuration. Driveway access is generally
difficult on upslope lots which require large retaining walls and a curving driveway.
(see Figure 2.4)
Figure 2.3: Building on flat site (left) and moderate slope (right) (Tweed Shire Council)
Figure 2.4: Building on steep slope (left) and extreme slope (right) (Tweed Shire Council)
2.2. Buildings on slope: the implications and solutions
If a site is flat, the topography may not influence the location and layout of the
building, but on a sloping site, the topography is likely to be a significant design
factor. The slope of a site and adjacent surroundings may affect access to sun and
views. For example, an east-facing hillside will have reduced afternoon and evening
sunlight, particularly in winter, and depending on the height and steepness, a south-
facing site may receive little or no sun during the winter months. The position of a
new house in undulating and hilly areas needs to be carefully considered to achieve a
practical design which does not look out of place. (Design Ideas for sloping sites)
12
2.2.1. Level changes
On a sloping site, a split level floor plan is the most cost effective way to develop a
site. However, this will usually involve several small sets of stairs between levels and
this can add to costs. Multiple levels may also limit the appeal of a property to
households with elderly, disabled, or young members. Changes in level can, however,
add considerably to the interest and appeal of the space, for instance, a change in floor
level can be used as an informal way of defining different areas within an open plan
space, as an alternative to using partition walls which restricts the appeal of the
openness of the space.
2.2.2. Upside down living
A sloping site often means that there is a view. One of the best ways of taking
advantage of this view is to reverse the accommodation to bring the living areas to the
top with the sleeping areas to the lower floors. The garage can be a complicating
factor in all of this. If the road is at the higher level, then the solution is for the garage
to be designed over the rest of the residential spaces. If the road is at the lower level
then there might be no alternative but for it to remain. However, it is likely that in
those circumstances the entrance accommodation will also have to share the lower
floor.
2.2.3. Building regulations
Building Regulations relating to disabled access can sometimes affect the design of a
house on a sloping site. Externally, they require that access ramps for slopes up to 1 in
15 should not be longer than 10 meters, and those for gradients up to 1 in 10, no
longer than 5 meters. Steeply sloping sites can, in the absence of a ramp, employ steps
at least 900mm wide with a rise no greater than 150mm and a distance between
landings of no more than 1,800mm. Additionally, if there are more than three risers,
handrails must be provided to at least one side. Internally the entrance floor must
contain a WC accessible by wheelchair.
2.2.4. Design guidelines for different amount of slopes
All development including grading on natural slopes below fifteen percent (15%)
should be designed according to the following guidelines (HRO) :
13
1. Building should be oriented with the contours utilizing the natural slopes. (see
Figure 2.5)
2. All development should be sited to avoid potentially hazardous areas and
environmentally sensitive areas as identified in the open space as well as to
avoid dislocation of any unusual rock.
3. The need for excavation or fill increases complexity of the construction as
well as adds on the cost.
4. For steeply sloping sites (e.g. in excess of 1:5) consider suitable split level
(stepped) schemes that relate more closely to existing ground levels should be
considered. Land should be carefully spaced around the building so that it
blends more successfully with the surroundings while creating further shelter.
(see Figure 2.7)
5. Excess fill should be either removed or carefully graded around the building to
suit the natural slope of the land.
6. Natural slope should dictate the form. Over excavation and creation of
artificial plateau should be avoided. (see Figure 2.6)
7. Natural drainage courses should be preserved, enhanced, and incorporated as
an integral part of the project design to the extent possible. Where required,
drainage channels should follow the existing drainage patterns to the extent
possible. They should be placed in inconspicuous locations and receive a
naturalizing treatment including native rock and landscaping, so that the
structure appears as an integral part of the environment.
8. Grading should be limited to the extent possible and designed to retain the
shape of the natural landform. Grading must be designed to preserve natural
features such as knolls or ridgelines. In no case should the top of a prominent
hilltop, knoll, or ridge be graded to create a large building pad; circulation
should be aligned to conform to the natural grades as much as possible. (see
Figure 2.5)
9. The use of retaining walls, plantable walls, and terraced retaining structures is
encouraged when use of these can eliminate the need for extensive cut or fill
slopes. Retaining walls should typically have a height of five (5) feet or less.
Plantable walls should be used instead of retaining walls above six (6) feet in
14
height. Terraced retaining structures should be considered when their use can
avoid the need for extensive manufactured slopes and retaining walls. (see
Figure 2.5)
10. Slopes steeper than two to one (2:1), appropriately designed by a geotechnical
engineer,
15
Figure 2.5: Design principles that must be taken care of (HRO)
Figure 2.6: Over excavation and creation of artificial plateau should be avoided (North Tipperary County
Council, 2009)
Development including grading on natural slopes between fifteen percent (15%) and
twenty-five percent (25%) should be designed according to the following guidelines
(HRO):
1. Grading should be utilized only for the construction and installation of roads,
utilities, garage
2. Deck construction with excessively high distances between the structure and
grade should be avoided.
3. Rear yard should not exceed twenty (20) feet measured parallel to the slope if
such yard requires a grading exemption.
4. Single-level residential structures should be oriented such that the greatest
horizontal dimension of the structure is parallel with, and not perpendicular to,
the natural contour of the land. The slope of the roof should be oriented in the
same direction as the natural slope. (see Figure 2.5)
Development including grading on natural slopes of thirty-five percent (25%) or over
should be designed according to the following guidelines (HRO):
1. Extensive manufactured slopes and retaining walls should be avoided.
2. Landscaping should be utilized to recreate the linear silhouette and to act as a
backdrop for structures. Trees that grow to at least one and a half times the
16
height of the structure should be planted between buildings to eliminate the
open gap and blend the rooflines into one continuous silhouette.
Figure 2.7: Step building design (Tweed Shire Council)
2.3. Clustering of houses
Clustering allows large portions of the original development to be retained in its
undisturbed natural state. To ensure that clustering of units does provide the open
space desired (City of Vernon- Hillside Guidelines 2008, 2008):
1. Small and larger lot detached housing (reduced yard setbacks);
2. Zero-lot line development (the equivalent of duplexes and townhouses but
with each unit owned in fee simple);
3. Multiple family development (e.g., duplex, triplex, etc, townhouse apartment);
and
4. Single-family strata development (any of the above where common areas are
collectively owned by two or more residents).
17
Figure 2.8: Standard large lot residential layout, mixed single family layout with open spaces, mixed density
layout with open spaces ( from left to right) (City of Vernon- Hillside Guidelines 2008, 2008)
2.4. Scenic opportunities
Scenic view opportunities from hillsides are recognized as valuable to both hillside
residents and the community as a whole. It is important, however, not to compromise
the geotechnical or environmental integrity of the slope to achieve views. View
corridors must be identified and strictly maintained for all lots to enable re-vegetation
in non-view locations on each lot. Additional criteria include (City of Vernon-
Hillside Guidelines 2008, 2008):
1. Buildings should be located to face the view and minimize interference with
the views of nearby residences. Buildings should be staggered where
appropriate to provide views between units that may otherwise limit the field
of view.
2. Buildings should be located so that upslope buildings have views over down
slope buildings. If massive grading of the slope is necessary to achieve this
concept, it may be necessary to reconfigure the subdivision or layout. The
priority is to avoid disruption of the terrain.
3. Development areas must be sited lower than the ridgeline so that the roof line
does not protrude into the ridgeline. Placement of roads, cuts and large or
continuous buildings near or over ridgelines should be avoided. Where gaps or
interruptions in the ridgeline are unavoidable due to road network
requirements, plant trees and vegetation in front of and behind the disturbance
to screen and restore a naturally appearing ridgeline. For grassland areas
where native trees are limited or nonexistent clusters of viable native trees
must be established to provide screening.
4. Development on ridgelines or the top of knolls is not supported and these
areas must be integrated as open spaces. Development should be sited and
18
designed in a way so as not to alter, disturb or remove significant scenic or
environmentally functional features of a parcel.
2.5. Conclusion
This chapter concludes that building should positively respond to the site and explore
the full potential of site. This chapter also tells about the implications and principles
of building design on different amount of slope to avoid the grading as much as
possible.
19
CHAPTER-3. BUILDING TYPOLOGIES, CONSTRUCTION
TECHNIQUES AND SERVICES
Most of the sloping landform in India lies in Northern region and North-Eastern
region. There large number of construction technologies is employed to suit the
terrain. Some buildings are constructed using locally available materials while some
are constructed using RCC. Thus there are large numbers of building typologies
prevalent in those regions.
3.1. Residential building typologies prevalent in North India
(Assessment Project Group of IIT Bombay, IIT Guwahati, IIT Kharagpur, IIT
Madras, IIT Roorkee, 2013)
1. Thathara with timber plank partitions and light weight sloping roof
2. Thathara with Dhajji-Diwari partitions and light weight sloping roof
3. Thathara with infills of stone masonry in mud mortar and light weight sloping
roof, dry stone and light weight sloping roof, brick masonry in cement mortar
and light weight sloping roof
4. Kath-Kunni walls with stone packing and light weight sloping roof,
heavy/stone sloping roof.
5. Mixed Kath-Kunni construction
6. Mixed rammed earth construction
7. Rubble stone (field stone) in mud/lime mortar or without mortar (usually with
timber roof)
8. Dressed stone masonry with cement mortar
9. Adobe block walls with sloping roof
10. Unreinforced brick masonry in cement mortar, cement mortar with reinforced
concrete floor/roof slabs, mud/lime mortar.
11. Unreinforced concrete block in lime/cement mortar (various floor/roof
systems)
12. Masonry mixed structure with reinforced concrete
13. Confined brick/block masonry with concrete posts/tie columns and beams
20
14. RC moment resisting frame with unreinforced masonry infill walls (see Figure
3.1), flat slab structure, open ground storey structure (see Figure 3.1), load
bearing masonry, open intermediate storey structure, mixed infills.
15. RC mixed structure with composite timber, bamboo and others
16. Dry rubble stone masonry with flat slab
17. Mixed dry rubble stone masonry
Figure 3.1: RC moment resisting frame with unreinforced masonry infill walls (left) and open ground storey
structure (right) (Assessment Project Group of IIT Bombay, IIT Guwahati, IIT Kharagpur, IIT Madras, IIT
Roorkee, 2013)
3.2. Residential building typologies prevalent in North East India
(Assessment Project Group of IIT Bombay, IIT Guwahati, IIT Kharagpur, IIT
Madras, IIT Roorkee, 2013)
1. Random rubble stone with mud/lime mortar
2. Dressed stone masonry with cement mortar
3. Mud walls with horizontal wood elements
4. Unreinforced brick masonry in mud/lime mortar, mud mortar with vertical
posts, cement mortar, cement mortar with reinforced concrete floor/roof slabs,
5. Unreinforced brick masonry in cement mortar with lintel bands (various
floor/roof systems)
6. Masonry mixed structure with timber, bamboo and other wood elements
7. RC moment resisting frame designed for gravity loads only, seismic features,
unreinforced masonry infill walls, flat slab structure, open ground storey
structure, composite steel
8. Steel moment resisting frame with brick masonry partitions, light weight
partitions
21
3.3. Construction techniques to be adopted while designing the building
in sloping sites
Design solutions/construction techniques like step building design, cut/fill
construction techniques, raising the building on stilts/poles, retaining wall
construction, drainage issues, seepage problems should be incorporated which
respects the site potential upto its full expanse and lessen the impact of landslide and
other issues.
3.3.1. Cut and Fill
This describes the process of carving out a level plinth on a sloping site in order to
build a space that is essentially designed for use on a level site. Any spoil that is cut
from the bank is reserved in order for it to be brought back to make up the levels on
the lower edge. With the cut-and-fill technique, material is removed from the uphill
part of the site and placed on the downhill portion to form a level surface (see Figure
3.2). The fill material may compact and settle later, and cause cracking of foundations
and walls. The extra load of a building may trigger a slope failure on unrestrained fill.
Retention walls and pre-compaction of fill may lessen the potential for that type of
slope failure. (How to Build on a Sloping Site)
3.3.2. Stilts/Poles
Building on stilts is one way of addressing steeply sloped sites (see Figure 3.2). This
avoids the need for expensive foundations and also negates the requirement for
tanking. The other benefit is that it leaves the ground untouched, allowing planting to
take place over much more of the site. It could also be implemented on multiple
levels. (How to Build on a Sloping Site)
22
Figure 3.2: Cut and fill construction (left) and stilts construction (right) Basements/Retaining walls (Tips for
building on a sloped terrain, 2014) (How to Build on a Sloping Site)
3.3.3. Basement and Retaining wall construction
When creating basements on sloped terrain, the walls are often subject to a lot of force
from the surrounding banks of land and therefore becoming retaining walls. Basement
construction (see Figure 3.3) may have to be strong enough to hold back
considerable banks of ground in which walls behave as retaining walls. In other
situations, such as building on a level plinth beside a natural or carved out bank, it
may be necessary to construct separate retaining walls. In certain circumstances it
may be cheaper, and visually more attractive, to construct a series of lower retaining
walls with the ground stepped between them. Structural engineers should be consulted
to be involved in the design of these structures, and detail design stage is important to
ensure good water proofing. Another option is stepping the ground by using low level
retaining walls, or gabion walls which are wire cages filled with stone or interlocking
concrete blocks that are subsequently filled with soil. (see Figure 3.4)
Retaining structures are relatively expensive but necessary in steep areas to gain
roadway space or to support the roadbed on a steep slope, rather than make a large cut
into the hillside. They can also be used for slope stabilization. Figure 3.5 presents
information on common types of retaining walls and simple design criteria for rock
walls (see Figure 3.7) where the base width is commonly 0.7 times the wall height.
Different construction principles are employed for retaining walls of different heights.
(see Figure 3.6). Figure 3.5 and Figure 3.4 shows the Gabion structures which are
commonly used for walls up to 5 meters high, particularly because they use locally
available rock and are labor intensive. These are commonly used for low gravity
retaining structure because they use locally available rock and are relatively
23
inexpensive. (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME
ROADS BMPS)
The use of retaining walls is not encouraged. These are only supported where they
preserve native undisturbed areas, address unstable native slopes or rock faces, or
form part of the neighborhood character. Where provided, the following criteria
should be considered in their design (Slope Stabilization and Stability of Cuts and
Fills- LOW-VOLUME ROADS BMPS):
1. Retaining walls should respect the natural character of the site and not present
a large uniform wall face that overpowers the site and disrupts animal
movements.
2. Retaining wall height should not exceed 3.0 m for roads and site specific
works, 1.2 m for yards. Higher walls may be appropriate where they are
articulated, have a surface texture/pattern, or where sufficient landscaping is
provided to screen the wall.
3. Smaller stepped retaining walls are employed instead of a large uniform wall.
The height and depth of the wall steps should be consistent with the natural
terrain or with the slope above and below the walls. For stepped retaining wall
systems, the walls must be designed to permit landscaping of the terraces that
will screen the wall, including irrigation to all terraces. Landscaping of the
terraces using mixed hardy native shrubs or trees is required. Width of each
terrace proposed must be sufficient to enable the landscaping required and
permit access for maintenance.
4. Retaining walls must be set back from utilities and the traveled portion of
roads to enable planting of screening landscaping.
Figure 3.3: Basement construction on sloping sites (Tips for building on a sloped terrain, 2014)
24
Figure 3.4: Typical retaining wall construction, Gabion wall and rock buttress (from left to right) (Slope
Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
Figure 3.5: Common types of retaining structures (Slope Stabilization and Stability of Cuts and Fills- LOW-
VOLUME ROADS BMPS)
25
Figure 3.6: Construction detail for retaining wall of height upto 2 m (left) and 5 m (right) (Slope Stabilization
and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
Figure 3.7: Typical rock wall construction for smooth backfill (left) and face with steps (right) (Slope
Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
3.3.4. Storm water management and Drainage system
Implement methods for collection, conveyance, control and treatment of storm water
is employed that mitigates potential impacts and emulates the areas natural water
cycle. This is required to limit runoff from new development based on the soil
capacity and sensitivity for ground recharge.
Having a sloping site may involve extra costs with drainage and. If site slopes down
from a road in which the sewer is fairly shallow then, pumped sewage system can be
used. But if the sewer is quite deep, then the slope may actually represent a saving in
cost, as the resulting house drainage will not have to be as deep. Sloping down from
the road means that surface water can collect around the base of the lower floor. This
may mean having to install a drainage channel to divert the water to soak ways.
26
Sloping up from the road may at first seem the best option, but many local authorities
will not allow surface water to go into the public sewers and many require that
precautions are taken to ensure that surface water does not flow onto the road. (Slope
Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
3.4. Roads:
Road designs are typically site specific and may require input from geotechnical
engineers and engineering geologists. Slope failures, or landslides, typically occur
where a slope is over-steep, where fill material is not compacted, or where cuts in
natural soils encounter groundwater or zones of weak material. Good road location
can often avoid landslide areas and reduce slope failures. When failures do occur, the
slide area should be stabilized by removing the slide material, flattening the slope,
adding drainage, or using stabilizing structures. Failures near streams and channel
crossings have an added risk of impact to water quality. Certain points to be taken
care of while designing road on sloping sites (Slope Stabilization and Stability of Cuts
and Fills- LOW-VOLUME ROADS BMPS):
1. Grading for the construction of access roads or drainage ways shall be
minimized so that the visual impacts associated with said construction are
mitigated to the greatest extent possible;
2. The construction of access roadways or driveways should be accompanied by
sufficient berming and landscaping/erosion control so that visual impacts
associated with said construction are promptly mitigated.
3. If the city engineer determines that no hazard to pedestrian or vehicular traffic
will be created, a garage or carport may be built to within five (5) feet of the
street right-of-way line.
3.4.1. Classification of access routes
Depending upon the terrain conditions, access routes may be classified as:
(California Coastal Commission)
3.4.1.1. Two-Lane Access Road
(see Figure 3.8)
1. Ingress and egress provided by 1 road.
27
2. Merges easily with existing access and conventional roadway designs.
3. 9' minimum width for each lane, required for fire safety.
4. On steep slopes, disturbed area for cut and fill will extend far beyond limits of
road bed and shoulders.
5. Careful drainage controls needed along road and modified slopes.
6. Broad road area may be visible from great distances.
7. Additional road may be required for emergency access.
3.4.1.2. Split Level Access Road
(see Figure 3.8)
1. Ingress and egress provided by 2 roads.
2. 9' minimum width for each lane, required for fire safety.
3. Split roads can be "stacked" to minimize visual impact, cut and fill can be
reduced.
4. Careful drainage controls needed along road and modified slopes.
5. Separate roads may provide emergency back-up when secondary access is
required.
Figure 3.8: Two lane road (left) and split level access road (right) (California Coastal Commission)
3.4.1.3. Single Lane with Pullouts
(see Figure 3.9)
1. One road providing ingress and egress.
2. Minimum width for lane should be 10' with turnouts, required for fire safety.
3. Land form alteration for cut and fill can be minimized.
4. Periodic road widening needed for pull-outs and turn-around.
28
5. Not suitable for high-density vehicle use.
6. May require secondary, back-up road for emergency situations.
3.4.1.4. Bridge
(see Figure 3.9)
1. Can span stream bed and most riparian habitat, if stream is narrow.
2. Most appropriate for high-use roads which cross perennial streams.
3. Structures can be expensive, need to assure sufficient width, turning angle and
height for emergency vehicles.
4. If bridge can be built without supports in stream, can avoid impacts to flow
and habitat.
5. Design must consider high flood events
6. A large bridge structure may dominate visual character of area.
Figure 3.9: Single lane road with pullouts (left) and bridge (right) (California Coastal Commission)
3.4.1.5. Culvert under Road
(see Figure 3.10)
1. Stream flow is channeled into a culvert and roadbed is constructed on top.
2. Only suitable for intermittent or low-flow streams or as part of area-wide
drainage plan for directing surface flow.
3. Road could provide primary access.
4. For stream crossings, a culvert will disturb banks.
29
3.4.1.6. Arizona Crossing/Ford
(see Figure 3.10)
1. Roadbed built directly into stream bed.
2. Stream bank and habitat at crossing will be disturbed by road.
3. Road should be a low volume road or secondary access.
4. If used for primary access, a secondary access should be provided for flash
flood events.
5. Due to low-profile, fords rarely alter visual character.
Figure 3.10: Culvert (left) and Arizona crossing (right) (California Coastal Commission)
Design criteria that should be considered while planning for sidewalks include (Slope
Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS):
1. Sidewalks must be set back from the road a minimum of 1.5 m to
accommodate snow storage (for cold regions).
2. Sidewalks are to be located on the same side of the road due to the winding
nature of hillside roads. The location for sidewalks must be set to maximize
the function as a safe pedestrian corridor through the development and provide
scenic views where possible.
3. Sidewalks on both sides of the road may be required for short distances to
provide walking linkage between roads and to provide improved sight
distances for road crossings.
4. The requirement for sidewalks on local cul-de-sac roads may be waived where
low traffic volume is generated, provided alternate off street pedestrian
facilities exist.
5. Curvilinear or meandering sidewalks and pathways may be used where they
eliminate long sustained grades. Varying offsets between the road and the
30
sidewalk may also be considered where it will save a significant feature or
reduce grading requirements.
3.4.2. Cut slope design options
In this technique, earth is cut from one pat and filled to other part to make access
route. For most of the hillside construction (slope between 0-60 percent), balanced cut
and fill (see Figure 3.11) is adopted because it can be done for most of the soil types.
In case of rocky terrains, a full bench cut (see Figure 3.12) is adopted for slope more
than 60 percent and through cut is adopted for slope between 0-60 percent. (see
Figure 3.13)
(Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
Figure 3.11: Balanced cut and fill for most of the construction on hill slopes (Slope Stabilization and Stability
of Cuts and Fills- LOW-VOLUME ROADS BMPS)
Figure 3.12: Full bench cuts for slopes exceeding 60% (Slope Stabilization and Stability of Cuts and Fills-
LOW-VOLUME ROADS BMPS)
31
Figure 3.13: Through cut (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS
BMPS)
3.4.3. Fill slope design options
Fill slope design solutions include typical fill (see Figure 3.14), benched slope fill
(see Figure 3.15), reinforced fill (see Figure 3.16), through fill (see Figure 3.17).
(Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
Figure 3.14: Typical fill (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS
BMPS)
Figure 3.15: Benched slope fill with layer placement (Slope Stabilization and Stability of Cuts and Fills-
LOW-VOLUME ROADS BMPS)
32
Figure 3.16: Reinforced fill. These can be used as an alternative for retaining wall (Slope Stabilization and
Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
Figure 3.17: Through fill (Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS
BMPS)
3.5. Practical considerations (landslide or slope stability)
The steepness does not necessarily correlate with the stability of slopes. Slope
stability depends on factors such as geologic materials, soils, moisture content and
vegetation cover. A comprehensive geotechnical investigation is required for
developments on slopes to provide the detailed information necessary to ensure slope
stability. Various studies have found that soil slips, which cause avalanche failures,
commonly initiate on slopes greater than 33%; slower moving earth flows occur most
often on slopes 30% to 60%. Nevertheless, serious erosion can occur on much
shallower slopes and the potential for erosion is greatest in the period between
removal or disturbance of vegetation and re-establishment of new vegetation.
Decisions on suitable methods for slope stabilization first require an evaluation of the
hazard. Deep mass movements (deep landslides) are difficult to control and require
engineering solutions. Shallower mass movement (shallow landslides) and erosion
processes are more suitable for control using bioengineering or eco engineering.
Bioengineering techniques combine engineering methods with natural or living
materials to protect or restore slopes and reduce erosion like using brush matteresing,
and the planting of shrubs, plants and trees to stabilize the soil.
33
Methods include the use of stone, steel, concrete and geosynthetics to stabilize or
shore up slopes that are liable to landslides. These methods should, where possible, be
combined with use of plants and trees to enhance the urban green space. (California
Coastal Commission)
There are various construction techniques by which landslide stability can be
achieved on slopes (California Coastal Commission):
3.5.1. Conventional Buttress Fill Slope
1. Extensive grading is required for steep slopes, since fill must be designed at
2:1 or 1.5:1 (horizontal to vertical).
2. Extensive surface disturbance and loss of habitat from fill area.
3. Finished slope does not blend with natural terrain min steep slope areas can be
varied to blend with natural terrain.
4. Surface and subsurface water flows must be controlled as long as fill slope
exists.
5. Drainage must be maintained; water cannot be directed to a modified slope.
3.5.2. Contour Graded Slope
(see Figure 3.18)
1. Extensive grading required if natural slope is steep; slope must conform to
local grading standards.
2. Some disturbance of surface area and habitat.
3. Finished slope can be varied to blend with natural terrain.
4. Surface and subsurface flows need to be controlled, as long as slope exists.
5. Portions of natural vegetation can be maintained.
3.5.3. Steep Geogrid Slope
(see Figure 3.18)
1. Slope can be constructed with little grading, even in steep terrain.
2. Finished slope can be steeper than a conventional buttress fill, up to 1:1.
3. Surface and subsurface flows need to be controlled as long as slope exists.
4. Can be constructed where space is limited.
5. Finished slope can be varied to blend with natural terrain.
34
3.5.4. High Retaining Wall
1. Can be constructed with very little grading.
2. Structures can be expensive, need to be carefully designed and constructed.
3. Drainage behind wall must be controlled as long as wall exists.
4. Useful for areas with limited construction space.
5. Rarely blends with natural terrain; surface treatments are possible.
6. Can be used for some landslide remediation.
3.5.5. Several Low Retaining Walls
1. Can be constructed with very little grading.
2. Only suitable for small slope instabilities, or for small cuts or fills.
3. Drainage behind walls needs to be controlled, as long as walls exist.
4. Small walls can be camouflaged be vegetation and often can blend into natural
terrain.
3.5.6. Gravity Wall/Crib Wall
1. Walls require more disturbance than retaining walls, but less than a buttress.
2. Since structure is open, surface and subsurface flows can go through the
structure; little drainage control needed.
3. Can be used for some landslide remediation.
4. Facing will not blend with natural terrain; some planting between the facing
elements may be possible.
Figure 3.18: Contour graded slope (left) and Steep geogrid slope (right) (California Coastal Commission)
35
3.6. Recommended practices
(Slope Stabilization and Stability of Cuts and Fills- LOW-VOLUME ROADS BMPS)
1. On steep ground (>60% slope) full bench construction should be adopted. A
narrow, single lane road with turnouts is constructed to minimize excavation
but road should not be much narrow so that it causes accidents
2. Cut slopes should be constructed in most of the soils using a cut slope ratio of
3/4:1 to 1:1 (horizontal: vertical). Flatter cut slopes should be constructed in
coarse granular and unconsolidated soils, in wet areas, and in soft or clay-rich
soils. Cut slopes in rock should have a ratio of 1/4:1 to 1/2:1.
3. Vertical cuts (1/4:1 or steeper) should be adopted only in stable rock or in very
well cemented soils, such as cemented volcanic ash or in-place decomposed
granite soil, where the risk of surface erosion is great and the risk of local
failures in the steep cut is low.
4. Unsuitable or excess excavation material should be disposed in locations that
will not cause water quality degradation or other resource damage.
5. Fill slopes should be compacted well in sensitive areas or when the fill is
constructed with erosive or weak soils to avoid landslides.
6. Retaining structures should be placed only upon good foundation materials,
such as bedrock or firm, in-place soils
3.7. Conclusion
This chapter tells about the residential building typologies prevalent in Northern and
North Eastern region of India and construction techniques to be adopted while
designing the building on sloping sites. This section focuses on cut/fill construction
techniques, construction of building on stilts, retaining wall construction, rock wall
construction, etc.
Road design criteria are also discussed focusing on cut/fill slope design options.
Landslide or slope stability is also taken into consideration.
36
CHAPTER-4. LANDSCAPING ON SLOPING LANDFORMS
Slopes offer a great challenge than flat ground when it comes to landscaping. The
biggest concern is usually the risk of erosion. Additionally, planting and maintaining
plants on inclines can be a difficult undertaking and take a little more thought and
effort than for a normal 'flat' garden but the results can be very unusual - and a much
more interesting garden can be created.
If slopes are very steep or complicated, landscape architect must be preferred, who
can advise on this aspect of your garden design, and make sure the design and the
works are structurally safe and sound.
4.1. Planning a landscape on slope
Planning a garden with slopes will surely be a challenge, but changes of level
certainly give any garden added interest, and add an extra aspect to sloping landform
design. Sloping garden designs will need to be very carefully thought about at the
planning a garden stage.
Designing a garden on sloping landform will depend on:
1. The severity of the slope (degree of slope or steepness of slope)
2. The size of the garden
3. Features to be included
Factors to be considered while planning a landscape on slope (Anderson) :
4.1.1. Drainage
If water drains to the down of the slope, water channel clues and channels are narrow,
then the erosion control will be a problem and slope may be more unstable than
required. This is something to keep in mind when landscaping is done slope
stability. To check this, a hole is dug and filled with water and time taken by water to
drain is noted. If drainage occurs within an hour or so, slope is relatively stable. If it
takes several days to drain, then slope is highly unstable. Water accumulation on the
slope is controlled because wet soil and mud on a steep hill can cause erosion and
slide issues.
37
4.1.2. Soil
Proper analysis of type of soil and is water holding capacity should be done. It will
decide the type of planting material that will best grow here and better secure the
slope. To check the type of soil, a hole should be dug somewhere on the slope,
preferably where landscaping is to be done and result is noted down. If soils on top
slides down the slope easier, then the soil is rocky or clayey. (Anderson)
4.1.3. Access and maintenance
Access to gardens on slope is necessary for maintenance, weeding, pruning and
watering, and can take different forms. If a very small garden, access can be made
from the edges. Larger gardens require access via paths, walkways or steps. Steps and
paths down the slope can be used to more appropriately access the terraced gardens.
(Anderson)
4.1.4. Rainwater and runoff management
Rainwater and runoff management is interrelated with irrigation, plant selection and
erosion control. Rainwater can prove harmful for a hillside garden. If unchecked, it
can cause serious erosion. Rain running down the hill and off the landscaped area into
the residential spaces is a problem. Rain can become an asset with proper design.
Terraces accomplish this inherently by providing level garden areas for the rain to
soak in and not runoff. Where a slope is not terraced, berms across the hillside with
narrow swales behind, and winding stone-lined creek beds can slow the movement of
water, allowing it to soak in. Garden at the bottom of the slope allows the last of the
runoff to gather and irrigate plants assembled there.
If there is a slope uphill from the residence, berms can also be used there to send
surface water around the house for use in lower gardens.
Aesthetically pleasing ground cover is also an easy solution to control water runoff. If
the slope is not too steep, a ground cover creates a clean appearance that is easy to
maintain. Ground covers such as Blue Rug Juniper, Baltic English Ivy and buffalo
grass are low maintenance and well suited to sloped areas. There are also flowering
ground covers for inclines like Creeping Phlox, Vinca Minor vines and Sweet
Woodruff. (Anderson)
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Boulders or rocks should be strategically placed around the plants to slow down any
water runoff. Stones offer a natural appearance, but they also trap the earth and
moisture within it.
4.1.5. Irrigation
Since hand watering of a landscaped area on slopes is not very convenient, there is a
need to install drip irrigation. Alternatively, on a low-water slope landscape, drought
tolerant plants can be selected; hand watering them first two summers can be done,
rather than installing irrigation.
Plants put at the top of a slope will get the least water, those in the middle somewhat
more, and those near the bottom the most, as water running downhill section is
soaking in more and more. Accordingly; top, middle and bottom regions are planned.
The most drought tolerant should go toward the top, and those that can tolerate more
water closer to the bottom. Exposure plays a factor too. And the direction the slope
faces will impact plant selection; southern and western exposures are hotter, and
northern and eastern can take plants that can stand less direct sun. (Anderson)
In addition to normal gardening issues mentioned above, particular challenges hillside
gardening must also be considered while planning a landscape on sloping site:
1. Erosion control and retaining the hillside
2. Rainwater and Runoff
3. Structural safety for landscape design
4. Plant selection and locationfor erosion control and relating to water needs
and exposure
5. Zoning and water behavior on slopes
6. Accessibility to the beds or plantings for maintenance and moving
7. Steepness of paths and steps, and safety aspects
Design considerations for gardens sloping up away from the house (or sloping
down towards the house)
A garden that slopes up from the home is one that can be seen to an even greater
degree than a flat site. It becomes a garden that can be terraced so as to bring
aesthetical values to the residence.
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1. Patio on a higher part of the garden, away from the house may look
interesting. Raised wooden decks can be attractive and they can be constructed
in such a way as to allow light to filter down to the windows of lower storeys.
2. The rest of the garden could be a series of attractive terraces probably with
steps.
3. Professional advice on structure should be taken and as to avoid water running
down the slope and collecting near the house. (Sloping Garden Design Ideas,
2014)
Design considerations for gardens sloping down away from the house (or sloping
up towards the house)
1. High level decking may look interesting.
2. The rest of the garden could be terraced with steps, and attractive planting and
groundcover to make space look aesthetically pleasing.
3. Advantage of great views. (Sloping Garden Design Ideas, 2014)
4.2. Landscaping principles on sloping sites
Hillside landscaping is the most challenging of all residential design problems.
Whether it is a natural undisturbed slope or one composed of cut-and-fill, there are
five essential principles that should be taken care of while designing on slopes.
(Gilmer)
1. Views should be preserved while solving problems.
Residence built within forested hillsides often cleared to increase the view. The trees
have vast roots that have held the soil in place for a long time, and when trees are cut
down the roots die and the soil becomes vulnerable. For this reason it is far better to
keep trees living whenever possible.
All the new trees, shrubs and structures proposed between the house and top of slope
should be taken care of. If trees are too large these can interfere with the view.
Trees planted on the slope itself can over time exceed the height of the slope to
encroach into the view. This is more important where a terrace may be graded into the
slope further down where trees are planted for shade. Trees with a low spreading
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canopy should be planted rather than an upright conical form such as a fir tree to
avoid repeated topping in the future. (Gilmer)
2. Slopes should be taken up gradually as possible.
A very gentle slope is not much different than a flats garden, but a steeper slope
certainly is.
Any time a slope is cut its integrity is compromised, therefore its more better if less
slope is cut. Cutting into a slope removes topsoil to expose subsoil, often heavy clays
or shale that are poorly drained or lack microbial action of a living topsoil. This is
why the planting on so many cut slopes and home pads on exposed subsoil are prone
to failure.
To preserve the slope, grading is done with a series of shorter terraces rather than one
or two very large ones graded with cut and fill. The larger terraces may require
extreme erosion control measures on the cut slope and a substantial retaining wall
must be specially engineered to hold the fill. Such walls are constructed with footings,
sometimes extending down to bedrock. Residences on moderate to extreme slopes are
prone to mudslides and slope failures in extreme weather. (Gilmer)
3. Plants with extensive root system should be used to bind the slope deep
underground.
Erosion and depth of the soil can be issues in a sloping garden, so choosing the right
plant for the right spot is the key. Slope is composed of different soil layers. When the
slope has been altered to create building pads, the natural binding of layers may be
lost or compromised. When extreme weather such as heavy rains falls on these sites
the water may travel through weaker seams to saturate layers deeper down. When
they become wet enough they lose their cohesive qualities and slough off in layers.
This is usually the cause of slope failures during rainy seasons.
When planting is done on slope, trees are selected with a deep network of fine roots.
The larger the root system the better, so trees are highly effective at binding subsoil
layers, with their extensive roots. There has been a great deal of study on the use of
fast growing drought resistant trees such as acacia, planted on slopes. They were
topped every year or two to force growth energy into expanding the roots for more
effective soil binding. Thought effective, the maintenance required by this technique
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precluded widespread use, but it is still recommended as a powerful tool for solving
site specific problems. (Gilmer)
What to plant on a sloping landform and where on the slope to plant various species
are key considerations. Shrubs require less maintenance than perennials, and in
addition, generally have a more extensive root system. Attractive foliage or flowers
can be chosen, and mix and matched to create attractive mounds of color and texture.
Plants like geraniums and begonias can be planted to protect slopes from being
washed away by rain. Good plants for a slope also include California lilac, Creeping
juniper, Purple coneflower, Rattlesnake master, Russian sage, Snowberry, Star
jasmine, common periwinkle, Siberian carpet cypress. Add plants that strengthen and
bind the soil while adorning the slope. (Anderson)
Shrubs which can be planted on slopes include Arctostaphylos, Ceanothus, Erica,
Helianthemum and Euonymous. Drought tolerant plant selections include Baccharis
pilularis 'Twin Peaks', Cistus, Correa, Grevillea, Mahonia, Rhamnus and Rosmarinus.
Ground cover plants are a perfect solution for covering sloping areas. Using ground
cover plants on any slope helps retain or hold the soil on the slope. Additionally,
groundcovers fill the area and crowd out weeds, making it easier to maintain. Hardy
perennials and shrubs can also be included as groundcover plants like hostas, sage and
snowberry. Ground cover plants such as Aubrietia are excellent for steep banks; they
suppress weeds, help stabilize the soil and needs low maintenance. (See Figure 4.1)
Planting pockets near the large boulders should be created for seasonal color or
creeping shrubbery like Cotoneaster or vinca. The stones can be treated with the moss
and to give them a weathered and time-elapsed effect. A small stream can also be put
in with for sound and visual effect.
While putting larger trees on slopes, certain things should be taken care of. Area
where the trees are to be planted should be leveled off so the tree stands on level and
not on a slope. A retaining wall can be put behind the tree to prevent dirt from
washing over the roots too much. Decorative stones can also be used to turn it into a
focal point. Too many upright plants should be avoided because they block the view.
Larger trees, shrubs and plants should be planted vertically, not pointing out of the
hillside. A small half well on the bottom side of the plant should be built to help retain
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water and allow it to soak into the soil around the plant. Smaller plants and ground
covers can be planted to fill in while larger plants take hold with the hillside.
Composting the soil usually proves helpfulcertainly if hillside soil is sandy or clay.
Hillside gardens, like all gardens should be well mulched. But the choice of mulch is
more critical. Things like straw, small bark or cocoa hulls will wash away easily.
Finely shredded redwood, or the coarser shredded rather than chipped mulches tend to
knit together into a mass, and are less (but not completely) susceptible to being
pushed downhill by rain. (Anderson)
Figure 4.1: Ground covers for steep slopes (Alders)
Certain points should be taken care of regarding landscaping on slopes:
1. Retain all trees, hedgerows and other existing features (e.g. streams, rock
outcrops) to provide a framework for the garden. Create new hedgerows of
mixed native species
2. Avoid large expanses of manicured lawns and suburban style gardens with
exotic species, these usually appear alien to their surroundings and do not
provide habitats for wildlife.
3. Plant the space between the house and the front boundary with trees in
informal clumps.
4. Trees and shrubs which are locally native will be easier to establish than more
exotic species, and in keeping with the character of the area.
5. On exposed sites, consider more substantial shelter planting of native trees to
help reduce the effects of cold winds and driving rain, whilst also increasing
privacy.
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4. Surface soils should be protected from rain spatter and runoff.
When rain falls on the slope, each drop that falls on bare earth dislodges particles of
soil. As runoff runs down slope, the velocity causes more particles to be scoured from
the surface of the soil. This is the basic cause of erosion. Anything that slows the
speed of runoff such as rocks or plants reduces scouring and protects the soil. Slopes
are planted to cover soil and to slow the runoff velocity.
Freeway slope planting is the most widespread example of how a single monoculture
of spreading plants such as ice plant or African daisy is used to protect the surface.
Although