NUMERICAL CALCULATION ON LOAD TRANSFER PROGRESS OF PILE FOUNDATION IN BEADED KARST CAVE STRATUM

Bearing behaviour of the pile in the beaded karst cave is very complex. It is of great significant to study the response characteristics coupling the load transfer of the pile and the stability of karst cave. Calculation on the bearing characteristics of the pile and the stability of beaded karst cave is made with the Plaxis 2D and Abaqus 3D.The numerical results show that the punching failure happens in the top rock when the ratio of the top rock thickness vs the cave span is small, while punching shear failure happens at larger ratio. There are multiple maxima of the side resistance around the pile because of the existence of the beaded karst carve. The number of the points is related to the top rock thickness, number of the karst carves and the floor rock thickness. The side resistance will fall down quickly around the free face of the top rock. The area size is related to the thickness of the surrounding rock and its displacement. The difference will become small under larger load. The maximum of the side resistance around the middle rock layer locates at the middle, and the maximum value declines with the increase of the middle rock layer thickness. Besides, the side resistance distributes as the isosceles triangle with the thin middle rock layer, while it distributes as ladder shape with thick middle rock layer. The thicker the middle rock layer, the greater the ladder span, and the more uniform distribution of the side resistance. However, the side resistance distribution around the middle rock layer is not related to the length of the pile. Only the side resistance around the floor rock layer is related to the length of the pile and the load value. The curve of load vs displacement of the middle rock layer is parabolic shape, and there is an obvious inflection point in the load-displacement curve. The vertical displacement of the middle rock layer grows with the increase of the length of the pile and the decrease of the thickness of middle rock layer. The greater the diameter of the pile, the greater the external load corresponding to the inflection point of the load-displacement curve, and the greater the vertical displacement of the middle rock layer. However, the influence of the pile diameter changing to the curve will become smaller when the pile diameter is large enough.