Variation in Collapsibility and Strength of Loess with Age

Abstract

In the natural state, both the well developed structure and notable strength of loess in China increase with depth (ie age). However, such variation becomes less prominent when the samples become saturated and the test results are analyzed in the light of a depth (overburden) denominator. Loess becomes weaker with increasing moisture content until, on reaching saturation, maximum settlement occurs. Such rapid settlement is called collapse. Collapse on saturation occurs at pressures of less than 0.2 MPa in loess of Holocene and upper Pleistocene age and under higher pressures in older loess. The terms “initial collpase pressure” (or residual structural strength) and “preconsolidation pressure” of saturated samples are technical synonyms. It has been demonstrated that many loess strata, at depth as well as those near the surface, collapse under overburden, the phenomenon being most remarkable in the western provinces such as Gansu, Qinghai and northern Shaanxi (Zones 1 and 2), and that the general picture of increased collapsibility from east to west across the immensely vast central Loess Plateau holds good for older as well as for younger soils.