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1.0 PROJECT DESCRIPTION
1.1 Basic Project Background and Information
Clark Water Corporation (CWC) is responsible for the provision of water and
wastewater services under a concession agreement with Clark Freeport Zone
(CFZ). To cope up with the projected demand due to the increasing number of
locators/investors in the CFZ, the existing water transmission and distribution need
to be expanded and additional storage facilities need to be constructed.
1.2 Project Rationale
CWC took responsibility for operating the existing water supply and wastewater
infrastructure systems in 2000 under a 25-year concession agreement. The
systems were constructed many years earlier to serve the US Clark Air Force base
which was vacated by US Forces after the eruption of Mt. Pinatubo in 1991 and
later turned into the CFZ.
The upgrading program intends to address the following major issues
.1.3 Options for Water Supply and Sewerage
Options recommended for augmentation of the water supply system envisaged for
Clark Water Corporation are summarized below.
1.4 Data for Preliminary Design
1.5 Scope of Preliminary Design Report
1.6 Final Preliminary Design Report
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2.0 BACKGROUND INFORMATION
2.1 Project Location
The Clark Freeport Zone (CFZ), in which CWC is responsible for the provision of
water and wastewater services under a concession agreement, is located in the
provinces of Pampanga and Tarlac in Central Luzon. The boundaries of the CFZ
are comprised of two distinct areas, i.e.
Sub-Zone:
o Boundaries: ODonnell River (north), McArthur Highway (east),
Abacan River (south), lower E slope of Zambales Mountain (west)o Drainage: ODonnell, Bongarit and Malago-Marimla Rivers and
Sapang Cauayan Creek
o Area: 23,600 ha
Main Zone:
o Boundaries: Sacobia and Bamban River (north), Abacan River (south)
o Drainage: Sacobia, Bamban and Abacan Rivers
o Area: 4,400 ha
The western portions of the CFZ are generally undulating ravines formed by
watercourses. The upper soil layer, at least 30 m thick, is composed of volcanic
ash deposited during the eruption of Mt. Pinatubo in 1991. This eruption blanketed
the Main Zone with ash fall deposits that resulted in the topography being
modified. Ground surface elevations within the CFZ range from 107 m MSL on the
floor of the eastern side of the valley, rising more than 275 m MSL on the western
side.
The main development features in the Main Zone comprise:
Airport, serving military and civilian flights (runway 3.2 km long)
Area IE-5: Area abutting Angeles, including shopping centers (including SM),
industries
Key industries include: (i) Luen, (ii) SMK, (iii) Nanox, (iv) Yokohama, (v) Texas
Instruments, (vi) Bertaphil.
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2.2 Climate
The climate of Clark, Subic and Tarlac belongs to Type I of the modified Coronas
Classification of Philippine Climate. This type is characterized by two pronounced
seasons, dry from November to April and wet during the rest of the year.
Particularly for Subic area, the months of May and October are considered the
transition period.
2.3 Topography and Drainage
The regional topography is characterized by rugged steep terrain of high relief on
the west and relatively flat alluvial plains on the east. Prominent peaks comprising
the western mountain range the Zambales Range, include Mt. Pinatubo (1,445
masl), Mt. Dorst (829 masl), Mt. Balakibok (843 masl), and Mt. Natib (1,243 masl).
A lone volcanic edifice - Mount Arayat, mars the otherwise f lat terrain of the
Central Plain of Luzon.
Six rivers drain through the project area: Marimla, Sapang Cauayan, Sacobia-
Bamban, Dolores, Quilanquil and Abacan Rivers. Headwaters of these rivers
emanate from the slopes of Mount Pinatubo. The volcanos eruption in 1991
blanketed the lowland region with centimeters of ashfall deposits, while proximal
valleys to the volcano were inundated and buried by tens of meters thick of
pyroclastic flow deposits. The attendant changes in topography and watershed
hydrology, and abundance of sediment resulted in frequent sediment-laden flows-collectively called lahars, along these rivers during enhanced rainfall. Ten years
after, rivers remain in a quasi-equilibrium state, thus a constant source of concern
of river and road management engineers.
The Dolores-Mabalacat-Sapang Balen River is one of the rivers and creeks
draining the Clark Freeport Zone (CFZ). It traverses the northwestern boundary of
the CFZ, and at its nearest approach is about 500 m from the proposed
wastewater treatment plant, Locally, the river segment above 110 masl is referred
to as Dolores Creek, and as Mabalacat River along the short segment transecting
Mabalacat town from 110 masl to 90 masl. Below 90 masl the river is referred to as
Sapang Balen River.
The Dolores-Mabalacat-Sapang Balen River is perennial stream draining a
catchment area of about 6 km2 above 100 masl. Stream gradient is less than one
degree along the stream segment below 160 masl. Channel morphology is
typically box-shaped, with channel depths of two to five meters, and widths of 15-
20 m. Active flow occupies less than two meters of the channel bed under
normal/low streamflow conditions. Channel bed is sandy with occasional gravel-
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dominated patches and boulders. No historical stream flow data is available for the
Dolores-Mabalacat-Sapang Balen River based on DPWH and NWRB data.
However, in November 2000 a low flow discharge was estimated at less than one
m3/sec along a section of the river at elevation 130 masl.
2.4 Regional Geology
The CFZ straddles the lower slopes of Bataan volcanic arc and the flat terrain of
the Central Plain of Luzon. The subzone falls from the upper slopes of Mt.
Pinatubo to the Sacobia-Bamban river valley. The Main Zone incorporates lower
volcanic slopes in the west and flat alluvial Central Plains in the center and east.
The site is underlain by a sequence of volcanics and volcanic-derived alluvium, as
summarized below:
Regional Geology
Unit LithologyRecent alluvium andlahars
Detrital deposits, mostly sand and gravel
Bamban Formation(east/downslope: MainZone) (Quaternary)
Upper partly continental tuff and tuffaceoussandstone sequence, lower section sandstone,shale and conglomerate
Quaternary Volcanics(west/upslope:sub-zone)
Andesite, basalt and dacite porphyries
Tarlac Formation (Mio-Pliocene)
Sandstone, siltstone, shale, limestone andconglomerate lenses, with andesite lavas and dykesin the upper sequences
Zambales UltramaficComplex (Cretaceous-Eocene)
Ophiolite sequence: dike complex and gabbro
Source: EIA Upgrading of CWC Waterworks prepared by bmp Environment and Community Care,Inc. and Black and Veatch, 29 September 2003.
2.5 Site Geology
Philippine Mines and Geosciences Bureau mapping indicates the Main Zone is
underlain by unconsolidated Recent alluvium in the Sacobia/Bamban River valley
and semi-consolidated and consolidated sedimentary and pyroclastic deposits of
the Bamban Formation beneath the alluvium in the river valley and at surface over
much of the reminder of the Main Zone. The Recent alluvium comprises boulder to
clay sized alluvial deposits laid down in a braided river environment, as well as
lahar deposits. Much of the subzone is underlain by the Moriones and Malinta
Formations. The younger (mid-Miocene) Malinta Formation comprises inter-
layered tuffaceous, thickly bedded sandstone and siltstone with occasional
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conglomerate. The older (early Miocene) Moriones Formation comprises locally
inter-layered sandstone, siltstone and conglomerate with some lapilli tuff.
2.6 Existing Land Use
Clark Freeport Zone is divided into two major zones the 4,440 hectares of fully
developed land in the Main Zone and approximate 29,000 hectares of developable
area, known as the Sub-Zone, within the provinces of Pampanga and Tarlac.
Industrial estates, tourism and recreational attractions and a huge civil aviation
complex, are currently occupying the Main Zone. The Sub-Zone is principally
intended for agricultural projects, corporate farming, agro-industries and food
processing.
The major land use of the Main Zone is the civil aviation complex that features two
parallel runways, each being more than 3000 meters long. Adjoining the airport
complex is an area appropriate for use by the Philippine Air Force.
The Main Zone also features a number of golf courses, the most notable of which
are Mimosa and Fontana. Residential areas are located at the center of the
recreational areas. Areas for industries are located on east, north and south of the
Main Zone.
2.7 Rainfall
The rainfall stations used in this project area are: (i) Iba, Zambales; (ii) Cubi Pt.,
Subic Bay, Zambales, (iii) Clark International Airport, (iv) Cabanatuan City, Nueva
Ecija, (v) Gabaldon, Nueva Ecija, (vi) Minalungao, Gen. Tinio, Nueva Ecija, (vii)
Science Garden, Quezon City, (viii) Angat Dam, Norzagaray, Bulacan and (ix)
Baler, Aurora.
These stations run from West to East (coast to coast), across Central Luzon,
Rainfall augmentation procedures was used to fill-up gaps in the rainfall records to
complete the records from 1961 -2007.
Subic and Iba, Zambales are located in the west coast of Luzon along the China
Sea coast and west of the Zambales Mountain Range. Clark is East of ZambalesMountain Range. The valley to which Clark belongs is the Central Luzon Valley,
which is east of the Sierra Madre Mountain Range.
The central valley which includes Clark has less annual rainfall than both the West
and East coast of Luzon. From January to April, the east coast to the center of the
Central Luzon valley, there is a very minimal rainfall. While from May to
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September, during the Southwest monsoon, rainfall is higher at the east coast.
From October to December, rainfall is higher at the East coast of
Luzon which is an effect of the Northeast monsoon.
For annual trend analysis, the only viable station in Central Luzon with continuous
record from 1961 to 2007 is the Angat Dam Station in Norzagaray, Bulacan.
The cumulative average seems to show a downward trend on annual rainfall. This
could be interpreted by some as an effect of global warming.
The 5-year moving average seems to show that the 5 consecutive wettest years
may have occurred from 1971 to 1975, while the driest 5 consecutive years are
1981-1985. It also shows peaks and lows every 5 to 10 years.
The 15-year moving average shows a downward trend from 1948 to 1991, and
upward trend after. This does not support the idea that there is a general
downward trend on annual rainfall. This seems to indicate that the rainfall series is
a part of a cycle, and there is a need of a longer record to be able to see the
complete cycle of changes in annual climate.
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3.0 DESIGN CONCEPTS AND CRITERIA FOR THE PRELIMINARY DESIGNOF THE ELEVATED RESERVOIR
In accordance with engineering standards, the Pulang Lupa reservoir shall be designed
to provide stability and durability, as well as protect the quality of the stored water. The
reservoir design criteria are intended not only to establish the structural integrity, but also
to ensure water system adequacy, reliability, and compatibility with existing and future
facilities.
3.1 Type of ReservoirReservoirs may be classified according to their function, relative position withrespect to earths surface, manner of operation and as to type of material of
construction.
The Pulang Lupa storage scheme is an elevated reservoir which is envisaged to
supplement the existing Lily Hill Reservoir or alternatively, could be the future
source of water supply to PSPC and adjoining locators. Pulang Lupa is a hilly area
within the proximity of PSPC at elevation 170 maslwhich could be developed to
provide the projected demand by operating independently or floating-on-the line in
tandem with Lily Hill Reservoir.
3.2 Definition of Source as Used in Sizing the New Reservoir
Any source classified as either permanent or seasonal may be considered a
source for the purpose of designing the new reservoir facility provided that the
source is continuously available to the system and at a minimum meets all
primary drinking water standards To be continuously available to the system
means that: (1) the source is equipped with functional pumping equipment (and
treatment equipment if required); (2) the equipment is exercised regularly to assure
its integrity; (3) water is available from the source year round; and (4) the source
is activated automatically based on pre-set parameters (reservoir level, system
pressure, etc.)
For the purpose of designing the new reservoir facility, the following are
considered sources:
1. Each pump in the well field comprising of wells pumping into the zone served
by that particular reservoir.
2. Each pump installed in a large capacity, large diameter well which could be
developed in the future to complement the existing pumps which can be
taken out of service without the need to interrupt operation of any other
pump.
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3.3 Storage Volume
The capacity of the reservoir shall be such that it will operate properly in
conjunction with the water treatment plant and appurtenant facilities. In general,
the reservoirs should be capable of supplying the incremental difference between
maximum day and peak hour demands. The capacity of a reservoir shall include
the storage needs of one or more of the following:
1. Operational storage (OS);
2. Emergency Storage (ES); and
3 Fire suppression storage (FSS).
The total capacity of all reservoirs within a service zone shall be equal to or in
excess of the storage needs required for operational storage, emergency storage
and fire-fighting storage.
3.4 Operational Storage (OS)
Operational storage is defined as the storage which can be drawn upon during
peak hour demands and subsequently replaced during low demand periods which
production facilities are being operated at nearly constant rates.
The amount of operational storage required will be 25 percent of the Average Daily
Demand (ADD) projected for PSPC and Australian Schools as follows:
Projected Average Day Demand (ADD):
PSPC = 6,000 m3/day
Australian School = 1,700 m3/day
Total: 7,700 m3.day
Required Operational Storage = 25% x 7,700 = 1,925 cu. meter.
Operational storage is the volume of the reservoir devoted to supplying the water
system while, under normal operating conditions, the source(s) of supply are in
off status. This volume will vary according to two main factors: (1) the sensitivity
of the water level sensors controlling the source pumps, and (2) the configuration
of the tank designed to provide the volume required to prevent excessive cycling
(starting and stopping) of the pump motor(s). The definition specifies that
operational storage is an additive quantity to the other components of storage.
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3.5 Emergency Storage (ES)
The amount of storage should be determined on the basis of an evaluation of the
water system and the duration of a service outage which could be expected.
However, facilities equipped with stand-by power generators will negate the need
for emergency storage in the planning of ground reservoirs.
3.6 Fire Storage
The quantity of fire-fighting storage will depend on the population of the service
area and shall be determined on the basis of the following schedule:
Area Population Fire Storage
Below 100,000 320 cu.m.
100,000 to 500,000 640 cu.m.
Above 500,00 950 cu.m.
3.7 System Pressure Considerations
The water level elevations of the reservoirs hydraulic shall be established through
system pressure consideration of the service areas following the detailed hydraulic
analysis which will be undertaken in consonance with the design criteria for new
and existing water systems.
3.8 Effective Storage
Effective volume is equal to the total volume less any dead storagebuilt into the
reservoir. The amount of effective storage may also be dependent upon the
location of the storage relative to the place of its use (whether or not it is in a
different pressure zone and what distance the water needs to be conveyed).
3.9 Dead Storage (DS)
Dead storage is the volume of stored water not available for distribution. The dead
storage is the volume below the outlet pipe which shall be 0.6 m. from the floor
level. The dead storage volume is excluded from the volumes provided to meet
the Operational Storage (OS) requirement for the system.
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3.10 System Pressure Considerations
The hydraulic design of the system shall be such that the average day demand
(ADD) shall be available to all service connections at 20 psi.
3.11 Design Life
Storage facilities are normally designed to serve the needs of the community for a
planned number of years, or to accommodate full system build-out (if they serve a
particular subdivision or planned development, or fulfill a condition of plat approval,
etc.) The design life for properly maintained concrete and steel storage tanks is
typically assumed to be about fifty years. Any other type of storage tank that doesnot have the historical longevity of these tanks needs to be evaluated on a life
cycle cost basis before being considered for use.
3.12 Ground Level and Underground Reservoirs
The following criteria shall apply to ground level, partially buried and underground
reservoirs:
1. Ground level, partially buried and underground reservoirs should be placed
outside the 100-year flood plain.
2. The area surrounding a ground level or below grade reservoir should be
graded in such a manner that will prevent surface water from standing within
15 meters of the structure, at a minimum.
3. When the reservoir bottom is below normal ground surface, it should be
placed above the groundwater table, if possible. If this is not possible,
special design considerations should include providing perimeter foundation
drains to daylight and exterior tank sealants. These are necessary to keep
ground water from entering the tank and to protect the reservoir from
potential flotation forces when the tank is empty.
4. Partially buried or underground reservoirs should be located at least 15
meters from sanitary sewers, drains, standing water, and similar sources of
possible contamination. Pipe typically used for water mains should also be
used for gravity sewers if they are located within 15 meters of the reservoir.
These pipelines should be pressure tested in place to 50 psi without leakage.
5. The top of the reservoir should not be less than 0.6 m. above normal ground
surface, unless special design considerations have been made to address
maintenance issues and protection from surface contamination.
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4.0 Design Standards and Considerations
4.1 Tank Materials in Contact with Potable Water
All additives, coatings, and compounds proposed for use in substantial contact
with potable water, such as those listed below, musthave ANSI/NSF certification
for contact with potable water. These materials also need to be carefully applied in
accordance to the manufacturers recommendations for that particular material.
4.2 Reservoir Appurtenant Design
All reservoir appurtenances should be designed to be water tight and shall have
means to prevent entry by birds, animals, insects, excessive dust, and other
potential sources of external contamination.
4.2.1 Reservoir Drains
Reservoirs shall be designed with drain facilities that drain to daylight or have an
approved alternative that is adequate to protect against cross-connection
contamination. The facilities should be capable of draining the full contents of the
tank without entry to the distribution system, or causing erosion at the drainage
outlet.
In locations where the topography is such that a drain to daylight is not feasible,the reservoir should be designed with a sump to allow for emptying the reservoir
through use of a sump pump.
If an outlet pipe is also used as a reservoir drain, it should include a removable silt
stop in the reservoir.
Drain lines may discharge directly to a dedicated dry well(s) provided precautions
are designed and constructed to insure protection against backflow into the
reservoir or distribution mains.
4.2.2 Reservoir Overflow Valve
Reservoirs shall be designed with float controlled valve that will prevent overflow
discharge which will create pressure build-up to effect automatic control of pump
operation through variable frequency drive (VFD) motor.
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4.2.3 Reservoir Atmospheric Vents
Reservoirs shall have a screened roof vent which should allow air into the reservoirat a rate greater than or equal to the rate that the water is withdrawn from thereservoir to prevent implosion or structural damage to the reservoir.
Upward facing vents shall not be used in any application. Screens shall be
provided on the vents to prevent entry by birds or animals. Ground level or
underground reservoirs should terminate in an inverted U construction with the
opening 0.6 to 0.9 m. above the roof or ground, and covered with No. 24 mesh
non-corrodible screen. Screens on ground-level reservoir vents should be located
within the pipe at a location minimally susceptible to vandalism.
4.2.4 Roof Drainage
The roof of the reservoir should be well drained. The slope of the reservoir roofshould be a minimum of 2 % (6 mm. vertical per 0.6 m. horizontal). To avoidpossible contamination, downspout pipes shall not enter or pass through thereservoir.
4.2.5 Tank Level ControlThe reservoirs should be equipped with a level control system designed tomaintain reservoir water levels within a pre-set operating range (operating
storage).
A high level and low-level alarm system with direct annunciation of notification tooperation personnel should be installed. There should also be a local levelindication, through ultra-sonic level measurement and transmitter.
4.3 Piping Material
Piping material used for pipelines constructed directly below the reservoir, andextending to at least 3 meters from the perimeter, should be sturdier material suchas ductile iron pipe or AWWA C205 steel pipe with a corrosion resistant coatinginside and out.
4.4 Operational Constraints and Considerations
All new reservoir designs are expected to meet all applicable OSHA and WISHA
requirements. In addition, reservoir design and construction should consider the
following issues:
1. Disposal of chlorinated water after construction and disinfection.
2. Disposal of tank drain line outflow and tank overflow stream.
Pls. verify what is the minimum slope.2% is not equal to 6mm vertical per 0.60m horizontal
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3. Impacts to system operation if the new reservoir were to be taken off-line in
the future for maintenance and/or cleaning.
4.5 Piping and Valving
Reservoir design shall include a provision for equalizing and isolating pipes and
valves in order to be able to perform maintenance.
Inlet pipe 150 mm. dia. shall enter each tank from the main pump discharge line
and shall be installed 0.3 m. below the roof level.
Each tank shall be provided with individual discharge pipe 200 mm. and shall be
connected to the main discharge line 300 mm. dia.
Each tank shall be provided with an isolation valve, which shall permit isolating the
tank from the water system. An air release/vacuum relief valve should be installed
on the distribution side of the isolation valve. A sample tap should be installed on
the tank side of the isolation valve to allow for the required sample collection
capability.
4.6 Geotechnical Engineering Evaluation
The geotechnical engineering evaluation provided assessment of the site
condition, recommendations and conclusions based on the results of the
Geotechnical Investigation conducted by Robei Drilling Services. The evaluation
involved an independent review of the results of the investigation and providingalternative recommendations for geotechnical design parameters for consideration
in the design of the design of the reservoir.
The evaluation also included assessment of results of the seismic structural
analysis related to the obtained soil bearing pressure.
4.6.1 Allowable Soil Bearing Capacity
The Allowable Soil Bearing Capacity recommended for use in the design
considered the critical soil formation underneath the reservoir which may still be
affected by the foundation loadings. While SPT values at foundation level are high
indicating either stiff or dense formation, down below at depth about 8m to 9m
below the existing grade are loose or soft formation critical for settlement. Thus, an
allowable soil bearing capacity reduced to consider the presence of the critical soil
layers of 200KPa as compared to previously considered allowable soil bearing
capacity value was recommended. This allowable soil bearing capacity is
recommended for use for normal static loadings. For transient loadings like
earthquake and wind loads an increased of up to 33% is considered acceptable.
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4.6.2 Foundation Pressure Overload based on results of StructuralAnalysis using Factored Load Condition
The calculated 350 KPa foundation pressure obtained from results of the structural
analysis using factored loads which included earthquake and wind loads, which
effectively reduce the Factor of Safety for this portion of the loaded area to close to
1.0, much less than the normal recommended FS of 3, may still be considered
allowable, since the indicated width coverage of the 350 KPa foundation pressure
is less than 2m and not expected to induce significant overstress over the critical
layer at depth 4m below foundation level.
4.6.3 Lateral Soil Pressure
Considering the nature of the reservoir wall which is not designed to allow
deflection to mobilize the active state of the soil, the coefficient of lateral earth
pressure at rest of about 0.50 is considered the more appropriate for use in the
lateral soil pressure calculations.
4.6.4 Reservoir Foundation Level above the 4 meters proposed depthof Embedment
The evaluation of the foundation assumed an embedment of 4m below natural
grade. It also considered in the analysis, results of the drillings below this depth. It
is, thus, recommended that during the construction of the foundation, excavationbe made to depth of 4m below grade. Then at overcuts, grade be restored to
foundation level using properly compacted suitable granular materials.
4.6.5 Effect of Sloping Grounds in the Vicinity to Soil Bearing Capacity
Based on the cross-sections provided, analysis on the effect of the sloping ground
adjacent the reservoir have also been undertaken. The recommended allowable
soil bearing capacity of 200 KPa for normal operating loads, already took into
consideration the slight reduction in soil bearing capacity due to the effect of the
adjacent slopes.
Under transient loading due to seismic and wind loads as represented by the
factored loads, the overload on the sides of the reservoir near the adjacent slopeparticularly at Reservoir 2 may induce vertical deformation due to foundation
overstress near the slope but this is expected to cover only the small area of the
overstress and not to affect the overall stability of the reservoir. The magnitude of
this deformation should be within the calculated maximum vertical deflection which
has been allowed in the design. Defects, if any, caused by deformation created by
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the overstress, may be repaired after the occurrence of the loading of the design
earthquake.
4.6.6 Effect of the Reservoir Loads to the Stability of the adjacentSlopes
Analysis has also been conducted to check if the reservoir loading will affect the
natural stability of the adjacent slopes. Although Reservoir 2 is located nearer the
adjacent slope, the reservoirs are located relatively distant from the slopes to
impose significant load on the slope. Under normal operating condition, the
reservoir loads have very minimal effect on the natural stability of the adjacent
slopes.
During occurrence of earthquake, the overloaded small portion of the side of
Reservoir 2 at about 350KPa, could, however, induce significant load on the
nearby upper slope to have some effect on its stability. But this is likely to be only
localized and not expected to have significant effect on the overall natural stability
of the slope nor the stability of the reservoir.
4.7 Reservoir Structural Design
This structural analysis and design report outlines the general structure design
criteria and parameters, as well as the structural design philosophy under the
approved codes and standards.
4.7.1 Codes and Standards
The requirements contained in the following codes and standards shall form a part
of these criteria, in the manner and to the extent specified herein.
The following Codes of Practice will govern under Structural Analysis and
Investigation:
a. NSCP National Structural Code of the Philippines Vol. 1, 5th Edition, 2001
b. ACI 318 Building Code Requirement for Structural Concrete, 1999 (as
adopted in NSCP 2001)
c. ACI 350 Code Requirements for Environmental Engineering ConcreteStructures, 01
d. ACI 315 Manual of Standard Practices for Detailing R.C. Structures, 1999
e. ASCE 7 Minimum Design Loads for Building and Other Structures, 1995
f. AASHTO Standard Specifications for Highway Bridges, 16th Edition, 1996
g. AWWA American Water Works Association
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h. AISC Manual of Steel Construction, Allowable Stress Design 9th edition
Specification for Design, Fabrication and Erection of Structural Steel (as
adopted in NSCP 2001).
The following Standards of Practice will govern under Materials and Construction:
a. PNS Philippine National Standards
b. ASTM American Society for Testing of Materials
4.7.2 Materials
4.7.2.1 Reinforced Concrete
Concrete Compression Strength: Concrete cylinder compression strength
measured in accordance with ASTM C-39-86 will be:
a. fc = 34.50 MPa (5,000 psi) for columns, beams/girders, suspended slabs,
footings and tank walls
b. fc = 20.70 MPa (3,000 psi) for others
4.7.2.2 Reinforcing Steel for Concrete
Reinforcing bars Yield Strength: Reinforcement bars minimum specified yield
strength measured in accordance with ASTM A615 will be:
a. Columns, beams/girders, suspended slabs, footings and walls:
fy = 414MPa (60,000 psi) for deformed bars 16 and larger;
fy = 276MPa (40,000 psi) for deformed bars 12 and smaller.
b. Ties, Stirrups:
fy = 276MPa (40,000 psi) for 12 deformed bars and smaller
4.7.3 Design Loading
The following loads considered in this report are those recommended in Chapter
2, Loads and Actions of NSCP 2001 and American Concrete Institute ACI-350-01
Code Requirements for Environmental Engineering Concrete Structures.
4.7.3.1 Vertical Loads
a. Dead Loads & Self Weight
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Dead load includes the weight of the structure and all permanently attached
equipment. If modeled, the self weight of the structure is usually generated by
the computer by assigning the appropriate material density and member
sizes.
Reinforced Concrete Density = 24 KN/cu.m.
Plain Concrete Density = 20 KN/cu.m.
Structural Steel Density = 77 KN/cu.m.
Unit weights other than the above shall conform to what is indicated in the
National Structural Code of the Philippines (NSCP 2001).
b. Live Loads
Live load includes the loads due to the intended use and occupancy of area
and moveable equipment.
Roof Live Load = 1.92 KN/sq.m.
Liquid Content = 9.81 KN/sq.m.
4.7.3.2 Lateral Loads
a. Wind Loads
Wind Load, W shall be calculated in accordance with the static analytical
method. The following data will serve as a guide in calculating the wind force
on the structure as a closed structure.
b. Earthquake Loads
Seismic or Earthquake Load, E may be considered as lateral forces that shall
act non-concurrently in the direction of each principal axis of the structure.
These loads are actually dynamic forces that shall be used, among which, for
structures 60m or more in height. However, an alternative static lateral force
is recommended based on rational analysis of well established principles of
mechanics.
Seismic load shall be calculated in accordance with the formula as given in
Section 208 of NSCP 2001 and using internationally accepted structural
engineering software.
4.7.3.3 Other Design Load and Forces
The proposed ground reservoir structure is considered as a special
environmental engineering concrete structure intended for conveying, storing,
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or treating water. Considering the location of the structure in elevated land
with high seismic risk area, the design analysis of the structure shall consider
the non-sloshing (lower) and sloshing (upper) portions of its content which will
induce hydrodynamic pressures on the structure; namely impulsive and
convective pressures, respectively.
4.8 Mechanical Design
Water level sensors may vary from mercury-type float switches to ultrasonic
sensors to pressure switches. Each type has a different sensitivity to water level
changes from fractions of inches to more than a foot. The tank designer will have
to account for the type of level sensor specified when determining the vertical
dimension needed for proper operation of the device. Manufacturers
specifications generally govern the determination of this dimension.
Once the pump control device is selected, the tank designer will be able to factor in
the vertical dimension when determining the other aspects of tank configuration,
such as the width and height, as well as the shape. The volume of OS should be
sufficient to avoid pump cycling in excess of the pump motor manufacturer's
recommendation. Historically, a rule of thumb was to limit the motor to no more
than six starts per hour. However, many manufacturers will warrant more frequent
cycling for their pump motors, depending upon the size of the pump.
4.9 Electrical System
Systems relying on non-elevated reservoirs (i.e., reservoirs that can only supply a
distribution system in whole or in part through a booster pump station) shall be
equipped with onsite back-up power facilities or, at least, with the ability to readily
connect to a portable generator.
Back-up power facilities shall be designed to start, through an automatic transfer
switch, upon interruption of the utility power supply.
The primary intent for recommending back-up power is to assure that the system is
pressurized at all times to minimize cross-connection contamination concerns.
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5.0 Design Drawings