ANALYSIS AND USE OF DISPERSION CURVE FOR CALCULATION OF BEARING CAPACITY

Abstract

Liquefaction of soil is one of the major factor of the failure of structures, occurring in the loose saturated sand deposits due to generation of excess pore water pressure. This pore water pressure generates when external shaking like earthquake forces are applied on the soil mass. Although the prevention of this phenomenon can be done by proper soil investigation and analysis. In this study empirical formulas are used for the assessment of liquefaction potential of the soil locally available at Delhi Technological University. SPT ‘N’ values, obtained from DTU soil report have taken for the analysis. Along with that the bearing capacity analysis is carried out using shear wave velocity and obtained results are compared with classical approach results. The shear wave velocity of the soil is evaluated using Multichannel Analysis of Surface Wave (MASW), which is the seismic technique to evaluate the shear wave velocity. Geophones are used for picking up seismic energy coming from active source. These energies are converted into the dispersion curve from where shear wave velocity evaluation along the depth is carried out using Winmasw software. The shear wave velocity is evaluated for four different locations of DTU. After getting adequate shear wave velocity values for these location allowable bearing capacity has been calculated by an empirical formula. Approach using seismic wave velocity is useful in saving the time and cost. Results shows the average shear wave velocity for the Delhi Technological area has found to be nearly to 300 m/s. This comparative study of evaluation of allowable bearing by using shear wave velocity with the classical Terzaghi approach showed that the alteration in allowable bearing capacity has found in very nominal range at these four specific location. Factor of safety from different analytical methods are presented, showing the difference in FOS value at various depth due to change in formulation of CSR (cyclic resistance ratio) and CRR (cyclic resistance ratio).