Study On The Rheological Properties Of Modified Sandy Gravel Based On Discrete Element Method

There are many complex geological environment problems in the process of shield construction, such as the relatively high content of sandy gravel, the poor plastic flow and so on. All of these may result in many technical problems, in order to ensure construction successfully, the conditions of soil must be improved. For example, modified materials can be injected to excavated soil in order to make the soil to present "plastic flow state". The purpose of this paper is to make numerical simulation to the sandy gravel of "plastic flow state" in order to analysis the rheological properties of the modified sandy gravel. Based on theoretical analysis, laboratory experiments and numerical simulation, the constitutive relation between sandy gravel and modified sandy gravel has been proposed, the distinct element model of modified sandy pebble soil has been constructed, the determination method of model parameters has been researched, some relevant tests have been designed, the rheology measurement device to modified sandy gravel has been developed, the rheological properties of the modified sandy gravel have been analyzed.The distinct element model of modified sandy gravel is established for researching the rheological properties at first. The sandy gravel was taken in a subway construction site of Beijing and was carried on the large-scale triaxial tests, and the mechanical properties were obtained in different confining pressures. The neural network was applied to invert the model parameters. The numerical experiment results with the laboratory test results in different confining pressures were compared so as to verify the accuracy of the model parameters.The modified sandy gravel is considered as a collection of pebbles wrapped mortar particles, the constitutive relation of the mortar particles is established. The model parameters were determined based on the experiments of slump and V-funnel test. The model was verified by direct shear test and the shear behavior of mortar was analyzed.According to the characteristics of sandy gravel, the equipment for measuring the rheological properties of sandy gravel was developed. The rheological parameters are obtained in different additions of modified sandy gravel which was identified that the soil belonged to Binham fluid. Based on applying yield stress and plastic viscosity to represent the rheological properties, the rheological parameters of "plastic flow state" are obtained. What’s more the mixing model was established to analyze variation of the rheological parameters of the sandy gravel under different pressure environments.In a word, the plastic flow properties of the modified sandy gravel which were researched in this paper play an important role in the development of modified materials, evaluation of the improvement effects and the selection of construction parameters.