Study On The Mechanism Of Pile Retaining And Supporting In Loess Foundation Pit

Row pile support is a fast and safe support method developed in recent years.In the past foundation pit support system,pile-row support is mostly used in the eastern coastal areas of China.With the development of foundation pit technology,it is widely used in the loess area of western China.However,the understanding of the present situation and mechanism of its work in the loess area still needs to be improved.and its design and calculation methods need to be improved.It is of great practical significance to carry out the research of pile drainage support in loess area.Based on the research at home and abroad,this paper summarizes the characteristics,calculation and design methods of single row pile support system.The support system is analyzed by the conventional calculation method and the calculation model established by MIDAS.The influence of various factors on the deformation and bending moment of the supporting pile is analyzed by changing the embedded depth of the pile,the diameter of the pile,the strength of the pile body and the water content of the soil.The results show that:1)In the loess area,when the cantilever pile is used,,The embedded depth of the pile has great influence on the deformation of the top of the pile and the surrounding soil,and combined with the economic safety of the project,The invention relates to a loess foundation pit row pile supporting system.and the embedded depth of pile is between 0.5 H and 1.0 H(H is the depth of foundation pit).2)When the effects of water are not considered,When pile diameter increases between0.6m~1.0m in loess area,the change of pile diameter has great influence on lateral displacement of pile body.The influence of pile diameter between 1.0m~1.4m on pile displacement is relatively small.Taking into account the economic type and rationality of the project,the pile diameter of 0.8m ~ 1.0m.3)In the loess region,the effect of water is not considered.Concrete strength has little effect on lateral displacement and bending moment.In engineering practice,the lower grade cement can be selected under the premise of satisfying the engineering safety,and the concrete of C25,C30 and C35 is suitable.4)Water content has great influence on the stability of foundation pit in loess area.With the increase of water content of loess,the shear strength of loess decreases greatly and the angle of internal friction decreases slightly.When the water content is less than 15,some cementing materials and minerals in loess melt into water less,and the structural damage of soil is very small;When the water content is greater than 15,the minerals in the loess and calcium carbonate are dissolved in the water.As a result,the bond property of loess particles is greatly reduced,and the structural failure of loess itself.5)After excavation,the foundation and surrounding soil will have different degrees of uplift.In addition,the horizontal displacement is relatively large at L/4 to 3L/4 from the edge line of the foundation pit.Especially in the middle of the edge line of foundation pit.Emphasis should be placed on the reinforcement of these positions in actual projects.