Numerical Analysis Of Composite Supporting Characters Of Upper Soil Nail Lower Pile Anchor In A Foundation Pit In Hefei

Foundation pit has a strong regional character,for different geological conditions and environmental factors,its supporting scheme is very different.The characteristics of foundation pit: the safety factor is small,both to ensure the safety and to control the cost;The risk is large,the influence of the external environment is more serious;The economic loss and social impact caused by accident of foundation pit are usually serious;Therefore,it is of great significance to study it.Taking a foundation pit in Hefei as the research object,this paper expounds the principle of foundation pit supporting,and analyzes its characters by numerical simulation,thus to find out the influence factors of the foundation pit characters.The depth of foundation pit is 18.85 meters,with a total of 5 layers of soil,and its geological conditions are preferable.It's adopt composite support scheme with upper soil nail and lower pile anchor,the soil nailed wall is 8.5 meters deep,the pile anchor is 10.35 meters deep,and the pile length is 14.35 meters.The main research method of this paper is to collect the relevant data of foundation pit,modeling and simulation by modern computer technology,and the calculation results are analyzed,to find out the influence factors of the foundation pit,qualitative and quantitative are used to research on it;Analyzed the influence factors of the maximum horizontal displacement of the pile by the orthogonal experimental design and analysis of data,and the optimization direction is prospected,which provides a reference for the same type of foundation pit optimization design.The conclusions are as follows:(1)The maximum horizontal displacement of foundation pit increases gradually with the depth increase of foundation pit excavation;The change of the horizontal displacement of soil nailing from top to bottom is not obvious,it shows that the integrity of soil nail and soil is better;The maximum horizontal displacement of the pile anchor support appears at the midpoint of the pile.(2)The surface settlement is relatively small during the excavation of the soil nailing part,and the surface settlement is obviously increased during the excavation of the pile anchor support part;The surface settlement needs to be considered In deep foundation pit.(3)The bending moment of the pile increases with the depth increase of the excavation,and the negative moment occurs in the pile after activating prestressed anchor,and the maximum bending moment of the pile is reduced remarkably,Therefore,the effect of prestressed anchor on the stability of the retaining pile is obvious.(4)The maximum horizontal displacement and surface settlement value of the foundation pit are obtained by numerical simulation,which meets the specification requirements,the rationality of the supporting scheme of the foundation pit and the practicability of the numerical simulation are verified.(5)According to the orthogonal experimental design and analysis of data,select the three factors of the pile diameter,pile spacing and length of the pile for experiments,and the results are concluded: the biggest influence factor of the maximum horizontal displacement of the pile is the pile diameter,The next is pile length and The last is the pile diameter;At the same time,the best combination of pile diameter,pile spacing and pile length in this experiment is found,and the optimization direction of pile is prospected.