Studies On One-Dimensional Consolidation Theory Of Layered Soils Considering The Effect Of Stress History

Although the stress history of soil has great influence on its compression and consolidation behavior, there is little study so far on the consolidation theory of soft soil taking account of the effect of stress history. In this thesis, one-dimensional consolidation theory of layered and over-consolidated soil was studied in detail.Based on the general analytical solution available for the problem of one-dimensional linear consolidation of layered soils, semi-analytical methods were proposed and established herein for solving the problem of one-dimensional linear or non-linear consolidation of layered soils considering the effect of stress history. Two corresponding computer programs named ODLCALOS and ODNCALOS were developed for the first time, in which important characteristics of soft clay such as its stress history and layered properties, non-linear property, the self-weight and time-dependent loading can be taken into account. The reliability of the programs was verified through comparisons with available analytical solutions. Once the effect of stress history of soils ignored, ODNCALOS turns to be the available computer program NAODCLS that was for solving non-linear consolidation problem. If the non-linear property of soils is ignored further, ODLCALOS will return to ODCALS that was developed based on the one-dimensional linear consolidation theory of layered soils.Both linear and non-linear consolidation behavior of layered soils considering the effect of stress history were then analyzed in detail by using ODLCALOS and ODNCALOS. A variety of consolidation curves were prepared and the influence of various factors on the development of settlement and the dissipation of pore pressure discussed. It has been shown that, besides the boundary conditions, the main factors affecting non-linear consolidation behavior of layered and over-consolidated soils are: the pressure of pre-consolidation (σ′_c) of each layer; the ratio of swelling index and compression index (c_e / c_c); the ratio of compression index and permeability index (c_c / c_k);distribution type of self-weight stresses; the thickness of soil layers and the distributions; the magnitude of load and the rate of loading (q_u and T_vc). Once the effect of stress history considered, there exists significant difference in numerical value between U_s, which is the average consolidation degree in terms of settlement representing the development rate of settlement, and U_p, which is the one in terms of average pore pressure representing the dissipation rate of excess pore water pressure. And generally, the settlement is smaller and the rate of consolidation is greater than these without considering the effect of stress history. In addition, to make easier the use of the consolidation theory developed herein, the consolidation degree vs. time factor tables were made for the non-linear consolidation of single layered and over-consolidated soil. Meanwhile, utilizing the actual soil parameters obtained from the consolidation tests based on GDS advanced consolidation testing system and the computer program developed, theoretical results were compared with the ones from laboratory testing. By this way, not only the consolidation theory developed in this thesis was again verified, but also the importance of considering the effect of stress history and non-linearity of soil in consolidation computation was illustrated.It is the work presented herein that for the first time takes consideration of the important factors such as the effect of stress history, non-linear characteristic of soil, soil self-weight stress and time-dependent loading in the study of consolidation theory in the same time, and provides efficient computer grogram and computation table for one-dimensional non-linear consolidation of over-consolidated soil. This develops consolidation theory and makes it more perfect.