Geotechnical Laboratory Setup

13 June 2021| 95 Comments| Avijit| 11:23 PM

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Geotechnical Engineering

The first requirement in geotechnical area is the testing of rock and soil sample. Although soil can be considered in homogeneous category but rock behavior is completely different from other materials used to build structures. Behaviour of rockis DIANE- Discontinuous, Inhomogeneous, anisotropic, Non-linerly, Elastic. The testing of soil or rock before taking any decision on construction is the first step and important step. The testing is primarily done to know the exact values of many geo-mechanical parameters. The characteristics may vary from layer to layer of the same soil or rock. Laboratory testing of rock and soil is the integral part of rock mechanics research and practice. A properly executed laboratory testing facility and program will provide geotechnical properties needed to perform geotechnical analyses and develop models. The samples needed for the tests which need to be carefully obtained in the field and properly stored to get efficient and accurate results. However, specimens which are disturbed upto a certain limit can also be used in some tests to calculate geo-mechanical parameters that are not affected by natural water content, Atterberg limits, etc. The maximum procedures are based on specific standards which are being followed worldwide. well maintained equipments and instruments, sensors, consistent laboratory routines, proper interpretation and sensitivity analysis of test results are very much essential to estimate the rock/soil characteristics of to accurately predict their behavior and to develop a efficient model.

The Geotechnical Laboratory should be well-equipped with testing equipments for evaluating all geo-mechanical properties of soils and rocks, which should include both physical and mechanical property determination apparatus including index properties, compaction characteristics, hydraulic characteristics, compressibility, rate of consolidation and sheer strength. In the market both conventional and sophisticated instruments are available. We should give preference to sophisticated instruments as numerical simulation software will give accurate result only if input parameters are perfect for modelling.

List of Equipment to be kept in the laboratory:

Common apparatus for geotechnical engineer:

Eqp 1: Moisture Content Testing Apparatus

For the determination of soil/rock moisture content using tools i.e. Cans, Oven, and Balance.

Eqp 2: Specific Gravity Determination Apparatus

For the determination of specific gravity of soil/rock and gravel specimens using apparatus: Volumetric Flask, Balance and Oven.

Eqp 3: Standard Sieve sets

Eqp 4: Hydrometer Analysis (Hydrometer, Mixer)

To determine the percentage of clay particle in fine grained soils

Eqp 5: Liquid Limit and plastic limit Test Apparatus

This Liquid Limit/ plastic limit Test apparatus will measure the liquid limit of soil. Casagrande Liquid Limit Device, and Tools; glass plates, cans, spatula and oven

Eqp 6: Modified Proctor’s Compaction Test Equipment

To determine optimum moisture content

Eqp 7: Unconfined Compression Test Machine

This equipment will be used to determine the unconfined compression strength of soil and its shear strength. UTM machine.

Eqp 8: Direct Shear Testing Machine

To determine shear strength and angle of internal friction for sand, soil and rock specimen.

Eqp 9: Core cutting machine

Eqp 10: Point load testing machine

For Research Purpose:

Eqp 1: Triaxial Shear Test Machine

For research and conventional testing to determine shear strength parameters. It has the capability to carry out test on a compacted or on an undisturbed samples to conduct tests under different conditions of consolidation (consolidated and unconsolidated soil tests) and different conditions of drainage (drained or undrained conditions). Measurement of shear strength and the stress-strain behavior and failure can be determined.

Eqp 2: Consolidation Test Machine

It can be used for research and conventional testing to determine parameters relating to settlement properties and behavior. It can be used to estimate both the magnitude and the time rate of settlement.

Space and almirahs
One small office room to install computer systems and to connect it with different apparatus
Separate almirahs for documentation
Separate space to store oriented geotechnical core
Mobile table for plotting purpose
Water spraying and supply arrangement to all rock cutting machines and apparatus.

For the planning of a mine excavation area, an important basis for excavation pit, land reclamation, beach nourishment etc. is the knowledge of the ground conditions, insitu stress, rock characteristics etc. The geotechnical investigation is the ultimate tool with its respective services which are carried out to determine rock behavior. The nature and extent always depends on the type of the geological structure, the difficulty to determination of the structure attribute and the expected ground conditions.

The main factors are-

Data Collection from field
Sutable and efficient geotechnical Investigation Programme
Field Investigation and Sampling data
Proper Laboratory Testing
And the preparation of Geotechnical Investigation Report

DATA COLLECTION

Topography maps
Geology maps and evaluation of regional geology conditions such as earthquake, faults, formation of soils
Climate and weather data

GEOTECHNICAL INVESTIGATION

List of technical standards to be applied (geotechnical site investigation, drilling methods in soil / rock, sampling of soil / rock / groundwater, field testing, geotechnical laboratory testing of soil / rock / groundwater characteristics)
Number, mapping / location, depth of boreholes
Soil and rock drilling & sampling methods (Soil Investigations)
Number of standard penetration tests (SPT)
Number of field vane shear tests
Number of disturbed and undisturbed soil samples
Number of undisturbed rock samples
Ground water sampling
Geotechnical laboratory testing programme

SAMPLING DATA

Work planning on manpower and equipment with respect to the Programme
Mobilization and De-mobilization of geotechnical drilling team, supervision personnel and equipment
Survey and Set-out of borehole coordinates
Proper Handling, Warehousing and Transport of Samples to the Geotechnical Laboratory

Drilling WorksDrilling works will be carried out by using drilling rigs having the capacity to drill in the sizes and to the termination requirements or depths instructed. We can provide rotary drilling methods into soil and rock strata applying different types of flushing media (depending on the existing / encountered soil conditions). In the particular case of encountering rock layers the appropriate boring / coring method should base on single tube core barrel or double tube core barrel being capable of recovering rock cores.
Soil Sampling & Soil InvestigationsThe undisturbed samples will be taken at certain intervals to the borehole depth termination and at the change of strata in borehole under application of various sampling methods and respective technical standards. Disturbed samples can be derived from selected recovered cores of standard penetration tests (SPT). For detailed guidance on the suitability of various soil sampling techniques in different types of soil, our geotechnical expert will provide professional advice. Sampling, handling, labeling and transport of samples will be executed in strict adherence with international standards and guidelines.Undisturbed sampling using the open-tube sample as thin-walled or thick-walled tube samplers can be applied depending on the encountered soil conditions whereas the thick-walled tube sampler is applied for stiff and dense soils and for soils containing coarse particles. For soil types that are difficult to sample, sample-retaining or closure devices are necessary.Undisturbed sampling using the piston sampler can be applied in low-strength fine soils such as silt and clay, including sensitive clays. It can be used either in boreholes or be pushed directly into the soil.
Rotary Core Drilling and Rock SamplingIn sampling by rotary core drilling, a tube system fitted with a bit at its lower end is rotated and fed into the rock mass by the drill rig via the drill string. This action produces a core sample within the tube system. A flushing medium is normally used. The sampling tool, i.e. the core barrel, can be a single tube, double tube or triple tube with a borehole diameter of 70 mm to 200 mm. The rock coring should be executed minimum 5m into the rock. For detailed guidance on the suitability of various core drilling and sampling techniques in different types of soil and rock, our geotechnical expert will provide professional advice.Samples can be obtained by this method as cores/cuttings. The single-tube core barrel only allows core recovery in consolidated formations, whereas double-tube and triple-tube core barrels can be used in all rock formations. The quality of the rock recovery achieved is determined by applying the following parameters as rock quality designation (RQD), total core recovery (TCR) and solid core recovery (SCR) ratios that have to be recorded and reported for each core run.
Standard Penetration Test (SPT)Standard Penetration Tests (SPT) shall be performed in boreholes in order to estimate consistency, relative density, and strength-deformation parameters of soils. In addition to this soil samples
obtained from SPT testing are used for classification purposes. SPT testing can also be carried out in weak weathered rock. The SPT testing shall be performed at certain numbers and respective intervals (it is common to apply an interval of 1.5m/test) to the borehole depth termination for all boreholes. The number of blows required to 15cm of penetration or fraction thereof is to be recorded. The first 15cm is to be considered as a seating drive. The number of blows required for the second and the third 15cm penetration is termed as “standard penetration resistance” or the raw “N value”.
Field Vane Shear Test (VST)Vane Shear Test (VST) is an in-place shear test in which a rod with thin radial vanes at the end is forced into the soil and the resistance to rotation of the rod is determined. VST addresses testing on land and for testing in drill holes or by self drilling or continuous push methods from the ground surface. VST provides an indication of in-situ undrained shear strength of fine- grained clays and silts or other fine geomaterials such as mine tailings, organic muck, and substances where undrained strength determination is required. Knowledge of the nature of the soil in which each vane test is to be made is necessary for assessment of the applicability and interpretation of the test. The test is not applicable for sandy soils which may allow drainage during the test. The test is routinely performed in conjunction with other field and laboratory tests. Cone Penetration Test (CPT)Cone penetration test (CPT) can be performed to evaluate effectively the site characterization. It is a valuable method of assessing the subsurface stratigraphy associated with soft materials, discontinuous lenses, organic soil, potentially liquefiable materials (silt, sands and granule gravel), generally excluding bedrock, very dense granular fill and strata containing cobbles and boulders. CPT is performed using a cylindrical penetrometer with a conical tip (cone) penetrating the ground at a constant rate. During the penetration, the forces on the cone and the friction sleeve are measured. CPT and the measured data can be used to evaluate soil conditions and parameters as follows:

Determination of soil strata variations and characterization of soil types
Evaluation of ground engineering properties (undrained shear strength, relative density, equivalent standard penetrations test values) may be derived from the measured data as mentioned above
Piezo-cones (CPTu) can be used to measure the pore water pressure and to assess hydrostatic head, consolidation and permeability characteristics
Data may be used to analysis the pile load-bearing capacity, foundation bearing capacity, foundation settlement, and liquefaction potential.
Cone penetration test (CPT) provides a continuous (although indirect) record of ground conditions, avoiding the ground disturbance associated with boring and sampling.
Remark: Interpretation of CPT results can be enhanced by the use of site specific correlations. Such correlations are obtained by performing laboratory tests on soil samples obtained from the location of the CPT tests.

GEOTECHNICAL LABORATORY TESTING

Index property tests (determining of soil classification)

Moisture content – determination of the moisture content of a soil as a percentage of its oven-dried weight.
Unit weight – determining the total/moist and dry densities – unit weights – of soil specimens.
Specific gravity – determination of the specific gravity of soil solids passing the 4.75-mm sieve (No. 4) by means of a water pycnometer.
Attenberg limits – determination of the liquid limit, plastic limit, and the plasticity index of soils.
Particle size distribution – quantitative determination of the distribution of particle sizes in soils, distribution of particle sizes larger than 75 μm – retained on the No. 200 sieve – is determined by sieving, while the distribution of particle sizes smaller than 75 μm is determined by a sedimentation process, using a hydrometer.

Engineering properties tests (determining of strength and deformation parameters)

Unconfined compression strength – determination of the unconfined compressive strength of cohesive soil of the axial load.
Consolidation test (one-dimensional consolidation properties) – determining the magnitude and rate of consolidation of soil when it is restrained laterally and drained axially while subjected to incrementally applied controlled-stress loading. Data from the consolidation test are used to estimate the magnitude and rate of both differential and total settlement of a structure or earthfill. Estimates of this type are of key importance in the design of engineered structures and the evaluation of their performance.
Consolidated undrained triaxial compression test – determination of strength and stress-strain relationships of cohesive soil when the specimens are isotropically consolidated and sheared in compression without drainage at a constant rate of axial deformation. Data from the undrained triaxial compression test are used in geotechnical engineering analysis to predict how the material will behave in a larger-scale geotechnical engineering applications. An example would be to predict the stability of the soil on a slope, whether the slope will collapse or whether the soil will support the shear stresses of the slope and remain in place. Undrained triaxial compression tests are used along with other tests to make such engineering predictions.

Rock Strength Properties Tests

Point load test – determining the point load strength index of rock. This is an index test and is intended to be used to classify rock strength.
Uniaxial compression strength test – determining unconfined compressive strength of intact rock core specimens. It is a test method for compressive strength and elastic moduli of intact rock core specimens under varying states of stress and temperatures. Unconfined compressive strength of rock is used in many design formulas and is sometimes used as an index property to select the appropriate excavation technique.

Chemical Analysis of Groundwater

pH value, sulphate content and chloride content tests – determining the aggressiveness of groundwater to concrete and steel structures.

INVESTIGATION REPORT PREPARATION

The detailed Report will be provided and prepared tailor-made for each project according to the respective project scope of service. The following table of content is a standard table of content that will be adjusted according to the project scope of service:Executive Summary

Project description
Description of the works performed with respect to the geotechnical investigation programme
Technical standards
Site conditions

Geotechnical Field Investigation

Drilling of boreholes
Soil sampling
Rock coring and rock sampling
Standard penetration tests
Field vane shear tests
Cone penetration tests
Final quantity report on field investigation works

Geotechnical Laboratory Testing

Index properties tests (moisture content tests, unit weight tests, specific gravity tests, atterberg limits tests, particle size distribution tests)
Engineering properties tests (unconfined compression strength tests, consolidation / oedometer tests, consolidated undrained triaxial compression tests)
Rock strength properties tests (point load tests, uniaxial compression strength tests)
Chemical analysis of ground water
Final quantity report on laboratory tests

Evaluation of Soil Conditions and Soil Parameters

Soil profile
Deformation properties of soft clay layers (pre-consolidation pressure and over consolidated ratio, compression, coefficient of primary consolidation index, cecondary consolidation)
Strength parameters (undrained shear strength, strength parameters from CIU tests, SPT-N values)

Groundwater

Ground water level measurement
Results on chemical ground water analysis and evaluation of level of aggressiveness to structures

Conclusions and Recommendation

Geotechnical soil conditions of the project site
Recommendation for building foundation methods, soil improvement methods … (acc. to the project scope)

Appendices