Evaluation of Elasticity Modulus of Clayey Soil from Undrained Shear Strength

The modulus of elasticity represents the soil stiffness; it was used to design and analyze the foundation, slope stability, retaining structure, etc. It is one of the main input parameters used in the finite element method for analyzing soil behavior. The scope of this study is to evaluate the correlation between the modulus of elasticity (E) and the cohesion of the soil (cu) for the remolded and undisturbed samples of clayey soil so it can assess the effect of lateral confining pressure on the soil modulus of elasticity. The unconfined test is chosen for remolded soil to identify the stress-strain behavior. After the experimental utilized is done, the test is modeled using the finite element method to study several states of soil. The PLAXIS program is utilized, and the results are compared with the practical results. The mohr-Coulomb model is chosen for this study because it is commonly used. Based on the results throughout this study, it can be concluded the simulation using the Mohr-Coulomb model of PLAXIS software gives good results for representing the unconfined compression test, so that for soft clay, the ratio between modulus of elasticity and cohesion is equal to (Eu = 30 cu) for remolded clay and (Eu = 55 cu) for undisturbed clay. While for stiff clay, it was equal (Eu = 65 cu) for remolded and (Eu = 120 cu) for undisturbed clay. The modulus of elasticity for the undisturbed is higher than for remolded clay, so the difference is almost double in the case of stiff clay. The lateral confining pressure affects the modules of soil; however, for soft clay, the range of soil modulus in the case of the drained test was (5 to 25 MPa), while the range is higher for the undrained case (18 to 54 MPa). Moreover, for stiff clay, the range was equal (11 to 100 MPa) for a drained test and between (18 to 100 MPa) for an undrained case.