Soil testing

Site investigation and soil testing

1. SOIL TTESTING Karthik V Assistant Professor KPRIET

2. INTRODUCTION: Soil is an essential construction material for Civil E ngineers . Hence, the accurate measurement of soil properties is very important in the design and execution of a civil engineering project . Soil is used as ( i ) construction material (Example: roadways, railways, earthen embankments, earthen dams), ( ii) Supporting material (Example: Foundations) and ( iii) Surrounding material (Example: Underground pipelines, tunnels ). Based on the type of soil and nature of the project a detailed test programme is planned.

3. NEED FOR SOIL TESTING :   Soil testing is an essential part of a Civil engineering project, the failure of a project due to improper/ inadequate soil testing is very expensive and sometimes irreparable. Hence, understanding the properties of soil and its consideration in the design are important.

4. The three important aspects in soil testing program are: Identification of appropriate soil test. Accurate measurement of soil properties. Analysis of test data and interpretation of properties for the design of structure

5. IDENTIFICATION OF TESTS Identification of appropriate tests is the most important aspect in the soil testing programme. The required tests for a given project depend on 1 . The nature of the project. 2 . The nature of the soil.

6. Nature of project: The important civil engineering projects where soil properties considered are: 1. Earthen embankment to store water 2. Road construction 3. Foundation 4. Filling behind a retaining wall

7. Nature of soil : Soil testing not only depends on the type of the project as explained above but also on the type of the soil . Shear parameters of clay soils are measured by performing either unconfined compression tests or Vane shear test or Direct shear test or Triaxial shear test . . The compactness of cohesive soils is measured in terms of OMC conditions (by performing compaction test) and the same is represented in terms of relative density (by conducting minimum and maximum density tests) in case of sandy soils.

8. CLASSIFICATION OF TESTS INTRODUCTION There are a number of tests available to measure the engineering properties of soils in laboratory and field . The tests to be performed depend on the type of soil and the nature of project.

9. LABORATORY TESTS The samples are either collected in an undisturbed state, in the form of core samples, or in a disturbed state, in the form of loose soils collected in bags . The laboratory tests, classified for the purpose for which the soil is being used are as follows: 1 . Classification tests 2 . Test to obtain physical properties of soil 3 . Shear tests 4 . Compressibility tests 5 . Other specific tests

10. Classification Test Soil Type Sieve Analysis Hydrometer Analysis Atterberg Limits Classification Of Soil Non –Cohesive soil Cohesive soil

11. PHYSICAL PROPERTIES OF SOIL Unit Weight Specific Gravity Moisture content Specific Gravity Pycnometer Method Sand Replacement Core cutter Method Degree of Saturation Porosity Void Ratio

12. Strength properties Direct Shear Test Vane Shear Test Trial Test Triaxial Test Unconfined Compression Test Direct S hear Test Soil Type Non –Cohesive soil Cohesive soil

13. Consolidation Properties Coefficient of Consolidation Compression Index

14. Other Special Tests Compaction Test CBR Test Permeability Tests Swelling Properties Soil Type Relative Density Test Standard Proctor Compaction Test Heavy Compaction Test Constant Volume Method Consolidation Method Free Swell Index Test Swelling Pressure Test Variable Head Test Constant Head Test Cohesive soil Non -Cohesive soil

15. FIELD TESTS A reasonably good undisturbed soil sample can be collected from clay layer . If the soil at the site is non-cohesive, it is difficult to obtain a good undisturbed soil sample. Hence the field tests are broadly classified as: 1. Field tests for foundations 2. Field tests for pavement design

16. Field tests for foundation design The following tests are useful in measuring the strength of soil in the field to estimate the bearing capacity of soils for foundation design. 1. Standard penetration test. (SPT) 2. Dynamic cone penetration tests (DCPT) 3. Static cone penetration test 4. Field vane shear test 5. Plate load test (PLT)

17. Field tests for pavement design The Commonly used field tests to obtain soil parameters required for designs of pavements are 1. Field CBR 2. Plate load test Field CBR test gives the CBR valves of soil in the field conditions. The CBR valves are useful in the design of flexible pavement.