Site Response of Organic Soils

A primary source of uncertainty in any evaluation of the seismic stability of the Sacramento-San Joaquin Delta levee system is the site response characteristics of the shallow organic soils that commonly underlay the levees. This paper provides an overview of recent research on the site response characteristics of organic soils using centrifuge and numerical modeling. The centrifuge modeling effort included the development of techniques to measure the shear wave velocity profile for a centrifuge model while in-flight. One-dimensional site response analyses using an equivalent linear procedure were performed with the measured shear wave velocity profiles and the modulus reduction and damping relationships determined from prior laboratory studies. Good agreement was obtained between the numerical simulations and the centrifuge model recordings

Estimation of small-strain shear modulus of embankment soils before construction using bender elements in compaction test

Design of railway track and highways on embankments with compacted fills often needs the value of small-strain shear modulus of the fill soil to be known before construction. This paper presents a new method of determining the value of Gmax using bender elements within the mould of laboratory compaction test which is generally performed to decide specifications of field compaction before construction. This method is much easier to perform and simulates the field conditions closely. A design mould configuration is suggested after due consideration to near-field effect and rigid boundary effect during wave propagation in the compaction mould. This process of wave propagation is also simulated using 3-D finite element model in ABAQUS to study the effect of aspect ratio of mould for different values of Poisson’s ratio of compacted soil. Accordingly, the testing procedure is laid out for bender element test after compaction of soil in the mould and applying vertical load to simulate the overburden expected at different depths of embankments. Using the proposed test procedure, the value of Gmax has been measured at different overburden values for several soil samples. The collected Gmax data is used to look at overburden effect and how it can be applied in design.by Amit Prashant, Himanshu Kotak and Prajakta R. Jadha