Influence of Overburden on Seismic Compression

Abstract

The state of practice for estimating ground settlements from seismic compression is the simplified procedure. This method was developed in the 1980's and gets its name from the relatively easy method of estimating shear strain demands from potential earthquakes at a site. This procedure is generally split into two parts; a procedure that estimates shear strain demands and a volumetric strain material model. The volumetric strain material model essentially correlates shear strain to resultant volumetric strain. The volumetric strain material model used in the simplified procedure is based on a study from the 1970's, where it was observed that cyclic volumetric strain is independent of vertical stress. Laboratory testing was conducted on a variety of soil materials that are able to experience seismic compression. Reconstituted samples were subjected to cyclic loading in an advanced simple shear testing machine known as the Digitally Controlled Simple Shear device. Factors such as density state and fines content were kept constant across soil categories. Test results show volumetric strain behaviour is dependent on vertical stress and the relationship appears to be power rule based.