Study On Dynamic Behavior And Structure Characteristics Of Loess In Different Areas

Loess is a kind of typical structural soil, which distributes mainly in the middle and west of China and has special district features and special sensitivity to water. Its special forming condition determines its special structural and different mechanics characteristics. In this paper, the study on mechanics characteristics of loess in different areas under static and dynamic conditions are carried on, which take the structural characteristics research as the breach, and the developing regularity of structural characteristics is preliminary analyzed, too.Firstly, the dynamic torsional shear tests on LanZhou, LuoChuan and YangLing loess under different water content and consolidation condition are carried on, the behavior of dynamic pore pressure, the dynamic stress and strain relationship, the dynamic modulus and the damping ratio are analyzed, the dynamic strength of YangLing loess is also preliminary analyzed, the test data for the analyses on loess structural characteristics under dynamic loading is prepared at the same time. The research results show that the dynamic pore pressure variety has very close relation with the water content and loading method. The curves of dynamic stress and strain relationship mostly show the hyperbolic model, it acts very well within small strain, whose configuration and value are influenced clearly by the water content. The curves of dynamic stress and strain relationship are also influenced by the consolidation effect, the dynamic shear stress creating the same dynamic shear strain increases with the consolidation effect, particularly for the remold loess. The original structure of loess is remarkably important to the dynamic stress and strain relationship of intact loess, more obvious under low water content. The curves of dynamic stress and strain relationship of loess in different areas(LanZhou, LuoChuan, YangLing)differ in the configuration and value, which change with the water content and consolidation effect. The maximum dynamic shear modular is influenced by the water content and consolidation effect, the lower water content and stronger consolidation effect, the larger is the maximum dynamic shear modular; The results of maximum dynamic shear modular of loess in different areas (LanZhou, LuoChuan, YangLing)under the same test condition are different, but almost in the same level. According to revising the handwork damping ratio values, the damping ratio increases with the dynamic shear strain, much faster under higher water content. The distributing area of damping ratio values under the same water content and different consolidation pressures shows the shape of reaphook, it has small damping ratio value within the small strain and turns to be a stable value after that. The water content contributes great effect on the damping ratio of loess., the higher water content, the larger is the value of damping ratio, the situation of intact loess is more serious than that of remold loess. Most values of damping ratio of loess are within 0.2~0.3, the value will reach up to 0.35 under high water content; The value varieties of damping ratio in LanZhou, LuoChuan and YangLing loess are not obvious. The dynamic strength of loess is influenced by the water content and consolidation effect, the lower water content and stronger consolidation, the larger is the value of the dynamic strength. The influence on the behavior of dynamic pore pressure, the dynamic stress and strain relationship, the dynamic modulus, the damping ratio and the dynamic strength by the inner and outer factors is basically achieved through altering the structural characteristics of loess, which is proceeding with the damnification of original structure and the forming of second structure of loess.With the help of confined compression test and data from the dynamic test, the varieties of the structural characteristics of loess in LanZhou, LuoChuan and YangLing under static and dynamic condition are analyzed, giving the explanation to the differences of structural characteristics and causes. The analyses to the structural characteristics are based on the stress structural parameter mp according to the confined compression test and the strain structural parameter mγunder dynamic condition, the two parameters both have excellent reflection to the variety of structural characteristics in different situations. After that, the different configuration of the two parameters are described, giving the explanation to that, for the completely confining and the finite confining conditions in different tests. The curves of structural parameters of LanZhou, LuoChuan and YangLing loess have similar or the same configuration and development under the same test condition, only differ in the value and grade. From the view of statistics, under the same water content and consolidation condition, the structural characteristics of YangLing loess are best, the following are LuoChuan and LanZhou loess. In other words, there is regularity with the locations of loess, that is increasing from the northwest to southeast of China. The form of structure influences the structural characteristics greatly, the flocculation-block structure is much stronger than the dispersive-coagulated-particle structure. The explanation to the forming causes and process of different loess structure is given, showing that the soakage of some water is good for the forming of flocculation-block structure of loess.