Research On Mechanical Performance Of T-shaped Bidirectional Cement-soil Deep Mixing Column In Deep Soft Soil

Deep cement-soil mixing pile have reinforced soft soil subgrade in China for over30years. From years of engineering practice, there are many shortcomings of deep cement-soil mixing pile reinforcing soft soil subgrade. Its basically behave in a few following respects:pile quality uniformity is poorer, reinforcement depth is not enough, much emerge grouting, the smaller pile spacing destroyed natural soil structure strength and so on. In consideration of the disadvantagges of tranditional cement-soil mixing pile, soft soil foundation is reinforced by T-shaped bidirectional cement-soil deep mixing column, which is firstly introduced in Panyu of Guangzhou. Because the pile style is rarely used in engineering practice, it is very necessary to further research.Three T-shaped bidirectional cement-soil deep mixing column, random selected in the second section of Huanglan fast municipal road in Panyu District, Guangzhou City, are used to core drilling in field, then unconfined compressive strength tests of drilled sample are done.Plate loading test is done for two of them.Finally,PLAXIS, two-dimension finite element analysis software, is used to research load transfer mechanism static load test of pile. Through the above jobs, the main researching achievements as follows:(1) Combining with core drilling in field and unconfined compressive strength tests indoor, the relationship between soil condition and the strength of cemented soil is studied, which shows soil condition have a major impact on the strength of cemented soil. The strength of cemented soil mixed by silty clay is the largest, mixed by medium sand with silt is in the middle, mixed by silty is the least.(2) Through analysing Q-s curves and s-lgt curves, obtained by the static load test in-situ, T-shaped bidirectional cement-soil deep mixing column has a high ultimate bearing capacity of single pile at a small settlement.Under sufficient bearing capacity, unequal settlement is much decreased.(3) Based on strain gage buried in pile, the relationship between column stress and depth can be obtained. Combining with the elastic modulus of soil cement in different depth, column axial force-depth curves and column friction-depth curves can be obtained by calculate. From above analysis, column axial force decreases with the increase of depth, and column axial force in upper column decreases faster than below column. As the load increases, the relative displacement of the pile-soil increases gradually, and the pile side friction play gradually from top to down. Column side friction is obviously sectionalized, and subsection is more obviously as load increases. In the depth range from0to4.5m of column, the pile side friction varies widely.(4) Through Simulation analysing by PLAXIS of finite element analysis software, the side friction of T-shaped bidirectional cement-soil deep mixing column decreases gradually from top to down, which shows time effect.Vertical displacement caused by T-shaped bidirectional cement-soil deep mixing column decreases from top to down.