ONE DAY SEMINAR ON GEOTECHNICAL ASPECTS IN INFRASTRUCTURE (Organized by IGS Chennai Chapter and Thiagarajar College of Engineering, Madurai) Date: 25.01.2014 Use of Geotechnical Software in Infrastructure Projects Dr. Subhadeep Banerjee Assistant Professor Assistant Professor Geotechnical Engineering Division Department of Civil Engineering Indian Institute of Technology Madras Chennai 600 036, India
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Use of Geotechnical Software in Infrastructure - Subhadeep Banerjee
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ONE DAY SEMINAR ON GEOTECHNICAL ASPECTS IN INFRASTRUCTURE(Organized by IGS Chennai Chapter and Thiagarajar College of Engineering, Madurai)
Date: 25.01.2014
Use of Geotechnical Software in Infrastructure Projects
Dr. Subhadeep BanerjeeAssistant ProfessorAssistant Professor
Geotechnical Engineering DivisionDepartment of Civil EngineeringIndian Institute of Technology MadrasChennai 600 036, India
How to handle a geotechnical problem ?Acquire land.
Reconnaissance of the sitesite.
Geologic history.
D t il dDetail survey and leveling.
Courtesy: Burland (1987)
How to handle a geotechnical problem ?
Sched le detail soilSchedule detail soil testing.
Field: SPT, Borehole, , ,plate load test etc.
Laboratory: Index h
Courtesy: Burland (1987)
property, strength, compressibility etc.
How to handle a geotechnical problem ?
Modeling:g
physical: not always possible
analytical: difficult for complex problem
Courtesy: Burland (1987)
numerical: FEM, BEM, FDM etc.
User Programmer
Analyst Engineer
Some Common Geotechnical Analysis Software
Plaxis (FEM) Pl i i f th t l ft d b t h i l Plaxis is one of the most popular software used by geotechnical consultants. it is preferred because of its user-friendly nature.
Plaxis is quite handy for plane stress problems.
There are lot of geotechnical features (such as anchors, geogrids, tunnels etc.) in-built in Plaxis. So just click and play….
Diff t tit ti d l f i li ti Different constitutive models for various applications.
Limitations It is a “Blackbox” type software.
It is so easy to use that the person who has no proper training in geotechnical engineering may possibly run a Plaxis analysis by simplygeotechnical engineering, may possibly run a Plaxis analysis by simply following some tutorials.
It is difficult to model non-conventional geotechnical problems (such l t i bl i l t i t )as, large strain problems, irregular geometries etc.)
Flexibility in modelling is absent.
FLAC d ib li it fi it diff l ti
FLAC (FDM) FLAC describes an explicit finite difference solution.
It can be used for rock mechanics problem as well.
It also has specific features such as structural elements e g to It also has specific features, such as structural elements, e.g., to represent anchors, piles, rock bolts or tunnel support, capabilities for thermal and hydro-mechanical analysis.
It i ti l l f l f d i bl It is particularly useful for dynamic problems.
Limitations It is NOT so simple in use.
It is difficult to model complicated geometries.
Dynamic analysis may sometimes encounter convergence problem
G St di t i i k f t h i l d
GeoStudio (Limit equilibrium) GeoStudio contains various packages for geotechnical and geoenvironmental applications:
1. Slope/W (Slope stability analysis)
2. Sigma/W (Load deformation analysis)
3. Seep/W (Seepage problems)
4. Quake/W (Dynamic analysis)
5. Temp/W (Geothermal analysis)
6. Air/W (Air flow analysis)
7. CTRAN/W (Contaminant transport)
8. Vadose/W (Vadose zone and soil cover analysis)
It is based on simple limit equilibrium method.Limitations
p q
The solution sometimes overestimates soil strength.
It is difficult to model complicated geometries.
It i l FEM
ABAQUS (FEM) It is a general purpose FEM.
It can model solid and water as two phases.
ABAQUS-explicit analysis is particularly useful for dynamic problems ABAQUS-explicit analysis is particularly useful for dynamic problems.
It offers various flexibilities in modelling.
It is NOT easy to use More suited for research
Limitations
It is NOT easy to use. More suited for research.
For large problems with many nodes ABAQUS analysis may encounter memory problem.
Convergence for highly non-linear problems is not easy to achieve.
ANSYS (FEM)
It is a general purpose FEM for mostly mechanical engineering applications.
It is quite efficient in dynamic analysis.
It is NOT suited for geotechnical problems
Limitations
It is NOT suited for geotechnical problems.
Couple flow analysis can not be done.
Limited number of constitutive models.
There are few moreThere are few more,
SASSI: Useful for soil-structure interaction analysisy
LS DIANA: Particularly suited for blast loadings.
SageCrisp: Couple flow analysis can be doneSageCrisp: Couple flow analysis can be done.
There are many more…..
Modern Finite Element SoftwareModern Finite Element Software
Ease of UseEase of Use≠
Ability to Use
especially true for geotechnical softwareespecially true for geotechnical software
Consequence
There may be many more if…
Problem 1: Stability Analysis of Slopes
Problem 1: Stability Analysis of Slopes
RL 107.00RL 107.00RL 104.00
RL 100.00 RL 96.70
RL 93 40
Ash Core Ash Core
4 m
7 m `Earthen Cover
RL 93.40RL 90.00
`Fly Ash Embankment ` Earthen Embankment
2.251
4m
5 m4 m
RL 80.00
The typical section of a dyke of NALCO ashpond at Angul OdishaThe typical section of a dyke of NALCO ashpond at Angul, Odisha
Plaxis model
The analysis was carried out using PLAXIS ver. 8.
Plane strain model with 15 noded triangular elements.
The base of the embankment is assumed as fixed base. The base of the embankment is assumed as fixed base.
The sides are horizontally restrained.
Material properties
Elevation Cohesion (kPa)
Angle of friction (⁰)
Unit weight (kN/m3)
B l 80 RL (F d ti ) 50 30 18Below + 80m RL (Foundation ) 50 30 18
+80 to +90 m RL (within starter dyke) 50 20 18
+80 to +90 m RL (Ash deposit) 5 35 1380 to 90 ( s depos t) 5 35 3
+90 to +100 m RL (Ash deposit) 5 30 13
+100 to +107 m RL (Ash deposit) 0 30 13
Material properties
Calculation stages
Results
FOS
Results
Total increment
Failure surface: It is not the conventional slip circles
Problem 2: Analysis of Excavation andProblem 2: Analysis of Excavation and Support Systems
Problem statement
The excavation carried up to a depth 11m from ground The excavation, carried up to a depth, 11m from groundsurface, was roughly rectangular in plan with dimensions of100m x 26m.
The excavation area was circumference by a 5-storybuilding on the north side and roads on all other sides.g
Problem statement
The sheet piles were driven to a depth of 30m below theground surface to support the excavation.
There were six levels of internal struts of three different There were six levels of internal struts of three differentsizes.
Steel H Piles were driven down to the bedrock at Steel H-Piles were driven down to the bedrock athorizontal 1.5m grid spacing within the excavation site.
26Sh il llSix no. of struts
11
26mSheet pile wall
11m
30m
H-Piles @ 1.5mspacing
Problem statement
The soil profile consisted of six different layers,
1.5m thick layer of fill
20.50 m thick marine clay layer,
9m thick silty clay layer,
7m thick medium stiff clay layer,
7m thick sandy silt layer and 7m thick sandy silt layer and
weathered rock (~5m).
Height of sheet pile
ll 30
SHEET PILE WALL
depth of excavati
0.0-1.5
wall, 30m
excavation 11mMARINE CLAY
STRUTSNo. excavation l l i
-22
SILTY CLAY
STRUTS
levels, six-31
38
SILTY CLAY
MEDIUM STIFF CLAYH-Piles-38
-45SANDY SILT
WEATHERED ROCK
H-Piles
-50WEATHERED ROCK
Excavation stages
Stages Construction sequences
1 Pile installation considering surcharge of 10 kPa for existing structure
2 Sheet pile driving up to depth of 30 m below ground
3 Excavation up to -1.4 m and installation of strut 1 at -1.0 m with a preload of 100 kN
4 Excavation up to -4.5 m and installation of strut 2 at -3.5 m with a preload of 150 kN
5 Excavation up to -6.0 m and installation of strut 3 at -5.25 m with a preload of 200 kNof 200 kN
6 Excavation up to -7.5 m and installation of strut 4 at -7.25 m
7 Excavation up to -9.25 m and installation of strut 5 at -8.75 m
8 Excavation up to -11 m and installation of strut 6 at -10.25 m
Struts
-1 H 350x350x12x19
Ground
1
-3.5 H 350x350x12x19
H 350x350x12x19
-5.25 H 400x400x13x21
-7.25-8.25 2H 400x400x13x21
2H 400x400x13x21
-10.25
2H 400x400x13x21
Excavation level
Ground water table
The initial position of the ground water table can be taken asground itselfground itself.
However, with each stage of excavation GWT will be lowered toth ti l l th i idthe excavation level on the passive side.