Experimental Study On Axial Force Transfer And Lateral Surcharge Response Of Pile Foundation Impaling Through Karst Caves Of Different Sizes

Pile in karst areas often impales caves of different height and often bears unilateral overload during the service period.Considering caves with different height and the lateral overloading response of the pile,the working mechanism of the pile impaling caves is not well understood.The lever loading device was designed,the strain of pile impaling caves of different height with the top of the pile bearing vertical load was test,the strain of pile body,the strain of earth pressure box and horizontal displacement under unilateral overload were test when the top of the pile is free,the transfer law of axial force and the response under unilateral overload of pile impaling caves of different heights were obtained.The results show that:(1)When the top of the pile bears vertical load,the settlement of the top for rock-embedded pile with the same length increases with the increase of the cave height.Before the pile enters the rock layer from the soil layer or the cave,there is an obvious interface effect of pile’s axial force transfer,that is the pile’s axial force at the bottom of the soil layer or the cave grows,and the growth rate increases with the increase of load.The pile’s axial force in the cave is "concave"along the depth,its magnitude of the concave increases with the increase of the load on the top of pile and the height of the cave.(2)When the pile bears unilateral overload,all of the horizontal displacement of pile,postpile earth pressure,pre-pile elastic resistance and bending moment increases with the increase of overload and the height of cave.When the pressure of the top of the pile is zero,the lateral displacement of the pile decreases with increasing depth,it is maximal at the top of the pile and zero at the soil-rock interface.With the increase of load,the peak value of the earth pressure on the pile shaft of ordinary piles drops to the upper position of the middle of the pile shaft in the upper soil layer,and the peak value of the earth pressure on the pile shaft of perforated piles drops to the lower position of the middle of the pile shaft.In the whole loading stage,the elastic resistance in front of piles increases first and then decreases from top to bottom,and the curve is "anti-C".In the final loading stage,both of the post-pile earth pressure and pre-pile elastic resistance increases first and then decreases along the depth in the soil section with one peak.The bending moment of the embedded pile and pile impaling caves increase with depth,it is maximal at the bottom of the soil layer and it decreases after entering the rock layer and cave.(3)Both of the vertical and horizontal bearing capacity of pile decreases with the increase of the height of the cave impaled by the pile.The pile section inside the cave formed by percussion drilling is not easily damaged by vertical compression.Under the unilateral overload,the pile impaling caves is most likely to rotate around the soil-rock interface and bend at the bottom of the soil layer.In engineering,it is recommended to increase the diameter and reinforcement rate of the upper pile in the soil layer and to embed the expanded section to an enough depth to improve the horizontal bearing capacity and to prevent the disaster of the pile impaling caves.