Study On The Influence Law Of Group Piles In The Active And Passive Zone Of Foundation Pit And The Improvement Of Design Concept

The passive pile and the supporting structure interact with each other,earth pressure on the supporting structure is reduced.Based on the excavation test of the unloaded composite foundation centrifuge,a numerical analysis model is established,combined with the results of the numerical analysis model,under the group pile condition.The two-stage analysis method is used to analyze the displacement behavior of single piles affected by excavation of foundation pits.The calculation method of soil pressure of support structures under composite foundation conditions is proposed.The interaction between support structure and underground outdoor wall is analyzed.Get the following conclusion:1.The variation law of single pile displacement behavior in composite foundation piles adjacent to foundation pit excavation is pointed out:when the pile spacing of composite foundation is greater than 4 times pile diameter,the composite foundation as a whole has less influence on the horizontal displacement of single pile;When the pile diameter is between 1-4 times,the horizontal displacement of the composite piles increases with the decrease of the pile spacing,and the horizontal displacement of the single pile changes about 30%;When the excavation depth of the foundation pit is less than 5m,the composite foundation has little effect on the displacement of the soil.When designing the foundation pit support structure,the interaction between the composite foundation and the soil can be neglected;2.The calculation method of active earth pressure under the influence of composite foundation under the rotation mode of the wall:the curve of the earth pressure obtained by the strip method along the depth direction is concave;the displacement between the layers pushes the earth pressure to the lower layer,and Active earth pressure combined force point is less than 1/3 of the wall height from the bottom of the wall;the earth pressure of the composite foundation is about 60%of the sand foundation(semi-infinite soil);3.To reveal the influence of group piles in the passive zone at the bottom of the pit on the passive earth pressure of the supporting structure,and obtain the calculation method of the passive earth pressure under the influence of the pile length,displacement rate and pile length of the pile bottom group;The larger the blockage effect of the piles in the passive zone on the soil is positively correlated with the displacement of the soil;4.The foundation pit supporting structure effectively reduces the earth pressure on the underground outdoor wall.If the supporting structure and the basement structure are connected as a whole through the concrete inner support,the earth pressure on the underground outdoor wall will be further reduced.The permanent design method for combination of foundation pit support and underground structure gives full play to the performance of the support structure.