Experimental Study On Rock Socketed Depth Effect Of Large Diameter Rock-socketed Piles

Rock-socketed pile is named after its pile end embedded in rock formation,and it is unique in all types of piles.Large diameter rock-socketed piles in our country has been widely used in construction,municipal,highway bridges,ports and other engineering field,its outstanding characteristic is high bearing capacity of single pile,small settlement,good seismic performance,strong adaptability and so on.At present,the application range of large diameter rock-socketed piles is becoming more and more widely.It has become a kind of pile type which is widely used in the western region dominated by mountain hilly terrain.In particular,there is a wide range of applications in port terminal projects in the upper reaches of the Yangtze river.For more than ten years,the problem of rock-socket depth effect on large-diameter rock-socketed piles has become the focus of academic and engineering circles,which is one of the important issues to be solved urgently.This paper first investigates the bearing behavior,the load transfer mechanism and the failure form of the rock-socketed pile under the vertical load condition by referring to the research on the rock-socketed piles in the actual engineering.Secondly,based on the Chongqing region,the bearing capacity and rock socketed depth effect of large-diameter rock socketed piles are studied by means of theoretical analysis,model test and finite element numerical simulation analysis.According to widely distributed in Chongqing area engineering rock type,put forward suitable for Chongqing area geological conditions of the optimal rock-socketed depth range,which aims to provide reference for the design and construction of large diameter rock-socketed piles.Finally,according to the measured data and numerical simulation results,the main factors that affect the bearing capacity,settlement characteristics and rock socketed depth effect of large diameter rock-socketed piles are analyzed in detail.The main research work and achievements are summarized as follows.(1)The vertical load transfer of rock socketed piles is an extremely complex process of interaction between pile,soil and rock.In the whole process of rock socketed pile subjected to vertical load,the lateral resistance of rock socketed section is earlier than that of rock socketed section,and the pile side resistance of rock socketed pile is earlier than that of pile end resistance.The main failure modes of rock-socketed piles are compression buckling failure,shear failure and shear failure of pile rock interface.(2)Mudstone rock-socketed piles and sandstone rock-socketed piles are all end-bearing friction piles,and their load-displacement curves are slowly.The distribution of pile-side friction along the pile depth direction is "big top and small bottom".For the mudstone rock-socketed piles,the upper peak appears between 0.04 L and 0.1L,and the lower peak appears between 0.79 L and 0.94 L.For the sandstone rock-socketed piles,the upper peak appears in the range of 0.08L~0.16 L,the lower peak range is 0.89L~0.94 L.With the increase of rock depth,the lower peak position has adownward trend.(3)The average lateral friction resistance of pile side is positively correlated with the strength of bedrock,and negatively correlated with the depth of rock socketed pile and the pile diameter.By increasing the diameter of pile,rock-socketed ratio and the strength of surrounding rock,the lateral friction resistance and bearing capacity of pile can be increased.(4)There is a rock socketed depth effect in rock-socketed piles,and there is an optimal range of rock socketed depth,but there is no maximum rock socketed depth.For the Chongqing area,the optimal rock-embedded depth of the mudstone rock-socketed piles is proposed to take 4D-5D,and the optimal rock-embedded depth of sandstone rock-socketed piles is recommended to take 3D-4D.