Study On The Pile-soil Interaction In Expansive Soil Of Mengzi,Yunnan

Expansive soil problems often be encountered in geotechnical engineering, characteristics of expansion after infiltration, contraction after evaporation in expansive soil may have a greater destructive effect on the upper structures. When the water content rate of the expansive soil around the pile increase because of moisture absorption or underground water level rises, it will lead to the pulling force due to the expansion effect on the pile caused by the expansive soil, which will cause pile and upper structures uplifting together in light structures, thus tensile force on pile body may lead to the tensile failure with affecting the construction safety. In order to reduce uplifting effect on structures caused by the swelling of the expansive soil when encounter water, foundation of the structures often adopt pile foundation. But because of the characteristics of expansive soil, pile-soil interaction effect in expansive soil differs from conventional one, thus the research of the effect of pile-soil interaction in expansive soil foundation has a certain practical significance.The paper carries out the research based on engineering example of pile in expansive soil -- the Funing Depot Project of Product Oil in Mengzi, Yunnan, it mainly includes the microstructure, the expansion rate, the expansive force, equivalent expansion effect of the thermal expansion interaction of pile and soil in the expansive soil, foundation treatment measures in the expansion soil and other aspects, the specific contents of the study is:(1) XRF, XRD, SEM and other experiments on the undisturbed soil samples based on the site sampling in Funing Depot Project of Product Oil, and the main methods of distinguishing the expansion potential of expansive soil are summarized; (2) The influence of different dry density and initial moisture content on the lateral expansion rate is studied by the laboratory tests of the remolded Mengzi expansive soil, the expansion force of different dry density and initial moisture content is measured by back pressure method of expansion and value of C and φ is measured by the direct shear tests; (3) Numerical simulation of pile-soil interaction in expansive soil considering the influence of rainfall on soil surface is carried out by the thermal structure coupling method; (4) The sensitivity analysis of the effect on the pile-soil interaction in expansive soil by setting the length and diameter of pile as the sensitive factors of pile-soil interaction; (5) Modified experiment on the groups of different amount of lime stone by using lime modified expansive soil based on the indoor test is carried out, which is aimed at the project to put forward expansive soil foundation treatment measures.The research results show that:(1) The main content of Mengzi expansive soil is montmorillonite, which accounts for 27.6%, and strong swelling potential could be determined according to the dry density, content of montmorillonite and free expansion rate; (2) Confined expansion ratio has a negative correlation with dry density, but it has a positive correlation with the density, moisture content and additional pressure; conclusion of initial moisture content causing little expansion force can be got by method of back pressure in expansion and expansion pressure has positive correlation with the significant changes by the increase of the dry density; (3) The transferring trend of load in pile is correct when simulating the expansion effect by using thermal expansion method, and area of pulling stress in pile has a top-down development, and the side friction above the "neutral point" is positive, negative below; change of the pile length has obvious effect on the controlling of the displacement of the pile’s top, but the pulling stress in the pile will be larger; (4) Mengzi expansive soil has almost no expansion if the quantity of lime is 6%, therefore it is suggested that expansive soil in layer affected drastically by the atmosphere lime be modified by using lime dosage of 6%～8% to eliminate the effect of expansive soil aiming at the project.