A Comparative Study on Determination Soil Deformation Modulus, Using In-Situ and Laboratory Plate Load Tests

Soil deformation modulus is one of the most complicated and important soil parameters, correlating between stress and settlement. The magnitude of deformation modulus is not constant. Its value, which varies in a wide range, depends on many factors. The soil deformation modulus may be determined using in-situ and laboratory tests, including consolidation test, triaxial test, Standard Penetration Test (SPT), Cone Penetration Test (CPT), Plate Load Test (PLT) and many other tests. Although the in-situ test results are more accurate in comparison with laboratory tests, but in-situ tests are more expensive and time consuming and practically these tests are usually difficult and sometimes impossible to perform.In the present research the in-situ plate load test results are employed to determine the soil deformation modulus. This test is then modeled in the laboratory and results are compared. To achieve this, after soil sampling from the site, the samples were classified after which their moisture content and unit weight were determined. The plate load test, modeled in the laboratory, was then performed on the undisturbed samples, taken from the site. In order to compare and establish a mathematical correlation between the results of these two groups (the in-situ and laboratory plate load tests), the load-settlement curves of all two group tests were plotted, after which the initial tangent slope, secant slope and unloading slope for each sample was calculated and plotted and the results were then compared. Considering the complicated soil behavior, the results of this research seem to be appropriate and can be used in practical civil engineering purposes.