| Due to the construction of high -speed railway and highway, it' s vital to solve two technical problems: the expansive (or other special formed) soil as filling and the control of the residual settlement of embankment on soft ground. And it may be one of the practical ways to treat the expansive soil with geogrid (as filling). By using reinforced-mat with other methods in ground-improvement and with taking into account the affection of filling rate on settlement of the ground, it is hopeful to control the (residual) settlement of soft ground. In order to meet the engineering requirement about settlement, this paper, based on large amount researches of domestic and abroad, focuses on studying techniques to improve expansive soils with geogrids and the functions of reinforced-mat in soft ground improvement. Therefore, tension tests of geogrids, pull-out tests between geogrids and expansive soils or sands, the related geotechical tests of soil' s properties, and model tests of soft ground improvement, were carried out for obtaining the engineering properties, quality index of geogrids, interaction parameters of friction characteristics between reinforcement and soils, and the affecting degree of factors influencing the lateral displacement (pile) rate during the construction of embankment filling with (residual) settlement considered restrictively. And the main conclusions are as follows:1. It has been put forward that quality index of geotgrids should be the tensile strength, strain, and strain rate, and the sizes of geogrid' s sample for strain test are suggested; The tensile strength of geogrid increases with increase of width of test sample, while the strain rate decreases as the pullout rate, length of sample increases, and when the pullout speed is larger, the strain rate varies with the width and length of sample, otherwise, the strain rate has little to do with them..2. Three kinds of springs were used to imitate different lateral stiffness of soft ground, and special drawers with sliding path were modeled as lateral displacement pile of embankment during its filling periods, with the function of reinforced-mat considered. On the basis of the data of tests designed by thogonal table L9 (34), three kinds of (factor, depth of layer, loading) state matrixes are obtained which could be used for procedure analysis by making use of the principle of information matrix conformation. And the relationship between the affecting degrees of factors influencing lateral displacement (pile) rate, the depth of layer, loading is researched by procedure analysis of loading, affecting factors and depth of layers respectively. The general laws of affecting degree of factors influencing lateral displacement rate with the depth of layers, in every layer and during loading process are gained. And the confinement effects (lateral restrained) of the sand-mat and reinforced-mat with loading are presented, with their differences after aperiod of loading also illustrated by comparing performances with each other, which will be a great progress for calculating the additional settlement resulting from shear deformation.3. Based on the pull-out tests data between geogrids and expansive soil/sands arranged by the orthogonal table L9 (34), the following conclusions are reached:1) The displacement-properties of pullout tests depend on the pullout speed. The law of factors' affecting degree, which influences the parameters between geogrids and soils in the pulling-out procedure, is obtained. With the concept of 'equivalent pull-out displacement (x )' brought forward, the whole process of pull out tests is divided into two process- " main process (when x 1.0)" and "residual process (when x 1.0)" , and three stages-static friction resistance stage, slip friction resistance stage, and residual friction resistance stage.2) The value of friction coefficient between reinforcement and soil varies with their definitions of friction, but each factor' s affecting degree influencing friction pa...
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