GEOTECHNICAL ENGINEERING – II (SOIL) DIVISION
The Geotechnical Engineering - II (Soil) Division undertakes studies related to Geotechnical Engineering discipline for various water resources, ports and harbour, nuclear and atomic power projects, etc. The division is well equipped with testing laboratory for determination of various physical, strength and hydraulic parameters of soil. These parameters are further used for studies using numerical modelling softwares and analytical methods.
Numerical modelling softwares used for conducting studies are :
> PLAXIS (Finite element software for static and dynamic stress analysis, seepage analysis of earth and rockfill structures)
> FLAC 2D (Finite difference software for static and dynamic stress analysis, slope stability, seepage analysis of earth and rockfill structures)
> TALREN, STABR (Program for slope stability analysis by circular slip surfaces)
STUDIES UNDERTAKEN
1) Stress and Deformation analysis of earth dams under static and earthquake load conditions
Stability of earth dam for static and earthquake load conditions is determined. Factor of safety of upstream and downstream slopes is evaluated using Limit Equilibrium method of slope stability considering various seepage conditions. Dynamic stability is determined using (i) Pseudo-static method and (ii) Detailed dynamic analysis. In detailed dynamic analysis site-specific acceleration time history for DBE event is used for computation of stresses and strains in the dam body. Remedial measures for stability of the dam, if required, are recommended.
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| Slope stabilty analysis by Slip Circle Method |
Dynamic Properties of soil for conducting detailed dynamic stability analysis
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Dynamic Properties of soil for conducting detailed dynamic stability analysis
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2) Seepage analysis of embankment dams, Recommending suitable remedial measures
Analysis is conducted by simulating geometry of the dam and hydraulic boundary conditions (Upstream and downstream water levels) in numerical modelling. Seepage properties (permeability, saturation, etc) of soil materials are used as input parameters. Characteristics of phreatic line, pore pressures, seepage discharges, flow vectors, flow nets, saturation, etc are determined in various zones of the dam. Suitable seepage remedial measures, if required, are recommended.
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| Phreatic line and Pore Pressure contours |
Seepage discharge through dam body and foundation |
Seepage remedial measure – Lining of upstream slope |
Geotechnical Engineering – I (Rock Mechanics)
Geotechnical Engineering–I(RM) undertakes - Laboratory studies, Field studies and Desk studies
(A) Laboratory studies: - The laboratory determined engineering properties namely density, unconfined compressive strength and Mohr Coulomb parameters are essential inputs in stress induced in stability analysis of underground opening to identify probable failure zones and in the design of effective support system for the safety of underground structures
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Significant projects- Koyna H.E. project, Virdi large minor irrigation project, Kumbhe H.E. Project; Talabira Mines .
Fully Automatic Compression Testing Machine with Accessories
(B) Field studies
To conduct in-situ deformability tests, In-situ shear test on rock and large size concrete, masonry or specially carved out rock mass blocks, Flat jack tests to determine insitu stress and deformability. Assessment of anchor strength, Evaluation of permeability, groutability.
Significant Projects–
Koyna H.E. Project, Bhakra H.E. Project, Shirota H.E. Project, Tata Power, Walwan H.E. Project, Kolkewadi H.E. Project, Kal H.E. Project, Raigad, Kumbhe H.E. Project, Ghatghar H.E. Project.
1) Flat Jack Test to determine insitu stress and deformability.
2) Permeability and Grouting Test: - Tests are conducted in NX size (54mm dia) boreholes from top of the dam or upsteam of dam to the foundation and further extended 10 m deep in the rock strata. After studying the permeability test results and core recovery, the remedial measures in the form of curtain grouting is suggested.
Significant Projects –
Hidkal H.E. Project, Songaon-Shivni Project, Chandas-Wathoda Project, Sindatalur Project.
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| In-situ permeability test in progress |
Rock cores from bore holes |
(C) Desk Studies : - Slope stability of hillock, 2) Slope stability of Rock cliff & Underground openings, using latest software.
Significant Projects – Tillari Interstate Irrigation Project, Arjuna Medium Irrigation Project, Insuli Border Check Post, Panshet H. E. Project
Slope Stability along hillock:- The Engineering properties such as Cohesion, angle of internal friction, Elastic modulus, Poisson’s Ratio, Permeability and dry & saturated density are determined for the soil and rock samples. Slope stability analysis is carried out with the help of MIDAS GTS NX and other available softwares. For unstable slopes remedial measures will be recommended e.g. piling/anchoring/grouting etc.
STRUCTURAL MODELLING AND ANALYSIS (SMA) DIVISION
1.0 LABORATORY STUDIES
Material Testing: Determination of Physical properties such as Young’s Modulus of Elasticity ,Poisson’s ratio,, Creep properties and Flexural strength etc., by applying electrical resistance strain gauge technology.
2.0 DESK STUDIES
I. Monitoring Post Construction behaviour of Hydraulic Structures:
a. Analysis and Interpretation of Instrumentation data installed on Hydraulic structures during construction such as Gravity Dams, Power houses and Water Conductor system etc.
II. Stability analysis of Gravity Dams by Finite Element Method (FEM) :
a. 2D /3D stress analysis under static and Earthquake loads using Pseudo-dynamic approach.
III. Mathematical Modeling of Hydraulic Structures:
a. 2D Dynamic analysis of Gravity Dams by FEM using Newmark direct- time-step-integration approach by applying Westergaard added mass theory using site specific accelerograms.
3.0 FIELD STUDIES
I .Assessment of Structural safety of water conductor system by in-situ strain measurement during hydro Test :
a. Measurement of Strains during prototype Hydrostatic test on Penstock
Bifurcations, Manifolds, Penstock ferrules, Water Pipeline ferrules etc.
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CONCRETE TECHNOLOGY
Type of Studies Undertaken:-
1. Design of cementitious grout mix by conducting laboratory and model studies, suggesting sequence, methodology and pressure for grouting in assessing suitability of grout systems towards control of seepage in hydraulic structures.
2. Estimation of placement temperature, lift height and lift interval by conducting temperature control studies on mass concrete and RCC dams by testing samples towards evaluation of strength, thermal, elastic and creep properties.
3. Identification of suitable repair materials such as epoxy based compounds and cementitious materials for strengthening/ rehabilitation of major hydraulic structures like dams, aqueducts, power house, stilling basin and conservation of monumental structures.
4. Assessing in-situ physical properties of concrete in gravity dams by testing extracted cores.
5. Evaluation of construction materials such as cement, bricks, fine and coarse aggregates for assessing their suitability in construction.
Brief details of studies undertaken:-
Temperature Control Studies of mass concrete and RCC dams:-
In mass concrete and RCC dams during construction rise in the temperature of concrete due to heat of hydration of cement may develop thermal gradient between internal temperature of concrete and surrounding air temperature. These thermal gradients results in tensile stresses in dam body and cracks may develop if the induced stresses are more than the tensile strength of concrete at early stages. Hence, careful determination of thermal properties and estimation of suitable placement temperature becomes essential to avoid cracking. These studies include evaluation of strength properties, thermal properties i.e. adiabatic temperature rise, thermal diffusivity, coefficient of thermal expansion, creep parameters and elastic properties such as modulus of elasticity and Poisson’s ratio of mass and roller compacted concrete. Such studies were carried out in CWPRS for dams such as Pollavaram, Indira Sagar, Sardar Sarovar, Koyna, Omkareshwar, Ghatghar, Nilwande, Bham, Gunjawani, Barrages across river Godavari etc.
Determination of thermal and creep properties of mass concrete
Assessing suitability of repair materials towards rehabilitation of distressed hydraulic structures:-
Due to ageing effect, natural disasters like earthquakes, poor construction quality etc. distresses in the form of cavities, cracks etc. occur in hydraulic structures which leads to seepage/leakage of water and may endanger safety. Therefore, for restoring the integrity of the structure along with seepage reduction rehabilitation of distressed structure becomes essential. Hence studies are carried out for selection of suitable repair materials like epoxies, polymer based mortars and concretes, fiber reinforced concrete etc. for their use in strengthening/ repairs of major hydraulic structures after determining their suitability. Laboratory studies are being carried out by various tests like mix viscosity, pot life, density, compressive strength, tensile strength (briquette), flexural strength, split tensile strength, modulus of elasticity, punching shear, bond strength with concrete (slant cone test), abrasion resistance, permeability tests etc. Such studies were carried out in CWPRS for more than 50 projects such as Koyna, Hirakud, Jawahar Sagar, Upper Indravati, Sardar Sarovar, Chilla, Chiplima, Anjunem, Krishnarajasagar, Almatti, Harangi, Moorum Silli, Shivsagar etc.
Evaluation of suitability of repair material in laboratory
Assessing suitable grout system towards control of seepage in hydraulic structures:-
Seepage problems occur in masonry and col-grout masonry dams due to poor construction quality, ageing effect, leaching of jointing mortar etc. and these distresses also affect the stability of masonry dams. Therefore, studies towards cement flyash slurry grouting using different percentage of flyash and bentonite are being carried out in laboratory. For assessing the suitability of grout system various tests such as flowability test- Marsh cone time of afflux, pH value, bleeding potential, jellification time etc. are being carried out. Also trial application of suitable grout is being carried out by casting and grouting the distressed stone masonry blocks and by conducting NDT, water loss tests and at pre-grouting and post grouting stages. Also strength properties, improvement in mass density and spread of grout are studied from extracted cores from grouted sample blocks. Studies in this connection have been carried out for Varasgaon, Temghar, Domihira, Warna, Dudhganga, Mahi dams etc. Further studies from Radhanagari, Mahan, Kutni Feeder, Ujjani, Kolkewadi, Maachhu-2 dams etc. are anticipated
Trial application of suitable grout system for masonry dams