Research On The Interaction Characteristics Between Expansive Soil And Geogrids By Pullout Test

The effective governance of expansive soil disaster is always a focus problem in the geotechnical engineering field. In the implementation process of the western expansive soil project of the Ministry of Communication, the slide of expansive soil cutting slope is treated successfully with reinforcement support technology by the research group. However, there is very little research results have been existed about the characteristics of reinforced expansive soils. In order to obtain the reinforcement mechanism and establish the relevant design method, it is necessary to study the mechanical characteristics between expansive soil and geogrids.According to the existing results of theoretical researches and test method, and on the basis of analysis of the various factors that exist which will has effects of interaction characteristics, we have been designed the test method under the condition of influential factors such as moisture content, overburden pressure, drawing speed, dimension of the geogrid, temperature with different kinds of expansive soils. And then we have carried out 192 contrast pullout tests by the pull-out test system of CSLB-01 with the Baise, Ningming expansive soil. Therefore, the relationship curve of the drawing force and pulling displacement of the geogrid are obtained that under different conditions.The results showed that: With the increase of overburden pressure, the drawing force of the geogrid increased and tends to slow after the peak, the stress process of reinforced soil can be divided into four stages: initial segment state, development state, local yield state, completely yield state. As the moisture content of filling soil increasing, the drawing forces have reduced. When it is more than the optimum moisture under the condition of wet heavy compaction test, the decrease of drawing force is not obviously. It is show that the normal working state of the role of reinforced soil interface friction changed little. With the width and length of the geogrid is increased which embedded in expansive soil, that suffered the large drawing force. Under the same conditions, the drawing force tested in the summer is smaller than in the winter. This indicated that the impact of soil temperature is also an important factor of the interface.Based on the relationship curve of the drawing force and displacement, the hyperbolic model can better reflect the mechanical characteristics between Ningming soil and geogrids, meanwhile, the softening and flow elastic-plastic model is more suitable for Baise soil. The differential equation between the drawing force and displacement is deduced on this basis. It is considered that take the pseudo-friction as a parameter may be more reasonable by means of the analysis of the interfacial parameters results ( c,φ,fφ). It is essential to multiplied by a safety coefficient about 1.5～1.8.Through the research on the interface parameters and interaction property between expansive soil and geogrids, and compared with the shear strength of expansive soil in direct shear test, we can know that the value of the interface parameters ( c,φ) tested by the pullout test is just only the 1/10 of the former. It is shown that the interface interaction is not the key factor of treated the expansive soil cutting slope successfully with reinforcement support technology. So it is supposed that we should open a new road about"steel wrap hoop"for the research of flexible support working mechanism in reinforced body.