Overview
1) Response of earth dams to strong earthquakes:
Dam in San Fernando destroyed after a rolling earthquake in 1971
Earth dams, when subjected to earthquakes, respond in a manner which is governed by its geometry, material properties and the characteristics of the earthquake ground motion. The energy loss characteristic is dictated not only by the hysteretic damping property of the material but also by the radiation of part of the energy through the non-rigid foundation. Seismic design of earth dams requires the understanding of these effects. In this context, design charts of seismic coefficients are produced, which are used in conjunction with the seismic slope stability analysis and sliding block displacements, in order to determine the safety of the dam. Slope stability analysis techniques determining the critical earthquake accelerations are developed for this purpose, which can be used for both static and earthquake loading conditions. New boundary conditions are developed so as to be able to incorporate the nature of the elastic foundations in the solutions.
Work is on hand towards developing a non-linear soil model with dynamic pore pressure generation which can be used with the two dimensional analysis. We have determined simple cyclic pore pressure parameters for soils which depend on number of cycles. These parameters can be used with either the simple slope stability analysis technique or with rigorous non-linear stress-strain analysis. The aim is to establish criterion of safe displacements in the simplified design method.
2) Prediction of design ground motion:
In order to predict the design ground motions for engineering purposes, it is necessary to understand the characteristics of the earthquake records. Using a database of more than 5000 strong motion records, these are analysed to find the best parameters to describe the ground motions and the way to predict them
3) The effect of local soil conditions on earthquake strong motion:
Strong motion records are affected by local soil conditions. For weak earthquakes, the soil may behave as a linear visco-elastic material while for strong earthquakes, the non-linear soil properties and the excess pore water pressure generated by earthquakes affect the surface record. An analytical solution is developed for multi-layered linear soil. A numerical solution technique is developed to account for the non-linear local soil conditions. Furthermore, the excess pore pressure which dissipates through the soil layers above and below the zone may create instability in structures after the earthquakes. This problem is also investigated.
4) Seismic design of foundations:
Foundations of structures may fail during earthquakes. The determination of the bearing capacity of the foundation to resist earthquakes is important. Bearing capacity factors for shallow strip footings are derived for seismic design of structures which are now being used in the design codes. Design curves are determined for bearing capacity of foundations near sloping grounds. Also the bearing capacity of deep foundations during seismic loading is being investigated at present. Since the prediction of the peak acceleration in a future earthquake is only statistical, the effect of exceeding the design earthquake is also investigated.
5) Seismic hazard analysis of engineering sites:
A GIS based seismic hazard analysis of engineering sites is developed. This is originally developed for Iran and the intention is to extend it to other parts of the world as necessity arises. The hazard is usually computed on a routine basis using probabilistic method. A feature of our hazard analysis technique is to homogenize the seismicity data with respect to magnitude, which involves recomputing magnitudes of past earthquakes.
Research supervision: Over the years, Dr. Sarma has supervised many research students leading to PhD and MPhil Degrees. Also, he supervises MSc dissertations and also fourth year undergraduate projects.