串珠状溶洞数量影响灌注桩顶部水平受拉特性试验研究

采用室内模型试验，对比研究串珠状溶洞数量对灌注桩顶部水平受拉特性的影响，为岩溶强发育区嵌岩桩的水平承载力设计提供试验依据. 结果表明：1）桩顶水平荷载相同时，上部土层段桩身水平位移、桩身弯矩（峰值）、桩侧土抗力随溶洞数量的增多而增大，单桩水平承载力随溶洞数量增多而明显减弱. 2）上部土层段桩身水平位移随桩顶水平荷载增大而增大，桩顶水平位移最大，嵌岩段很小甚至为0；弯矩M -深度z曲线整体呈抛物线形，桩身弯矩在土岩界面和上层溶洞与底板界面呈现2个峰值，弯矩的变化仅仅影响到上层溶洞及其底板，第2层溶洞及其以下的弯矩几乎为0，土岩界面弯矩最大、截面最危险；土抗力p-深度z曲线呈“凸肚”形. 3）溶洞数量增加，位置越高，p-y曲线越容易收敛，可以采用p/pub=α（y/y50）β拟合土层段的桩身p-y曲线. 溶洞数量对α与β值变化幅度的影响较小，α与β值变化幅度体现p-y曲线随深度变化的敏感度，两者敏感度随溶洞数量增多而增大. 4）工程桩刺穿串珠状溶洞时，为了提高单桩水平抗拉能力，建议采用注浆法改善上部岩土性质，加大土岩界面处桩身配筋率，并将桩身嵌入上层溶洞底板一定深度，防止基桩在土岩界面处发生弯曲破坏.

Experimental Study on Influence of Number of Beaded Karst Caves on Top Horizontal Tensile Characteristics of Cast-in-place Piles

Indoor model tests were used to compare and study the influence of the number of beaded Karst caves on the top horizontal tensile characteristics of the cast-in-places piles， so as to provide an experimental basis for the design of horizontal bearing capacity of embedded rock piles in Karst strong development areas. The results show that： 1） when the horizontal load at the top of the pile is the same， the horizontal displacement， pile bending moment （or peak value）， and pile side soil resistance of the upper soil section increase with the increase of the number of Karst caves， and the horizontal bearing capacity of the single pile decreases significantly with the increase of the number of Karst caves. 2） The horizontal displacement of the pile body in the upper soil section increases with the increase of the horizontal load on the pile top. The pile top horizontal displacement is the largest， and the embedded rock section is very small or even 0. The bending moment M-depth z curve is parabolic in shape， the pile bending moment at the soil-rock interface and the interface between the upper layer Karst caves and the base plate presents two peaks， the change of bending moment only affects the upper layer Karst caves and its base plate， and the bending moment at the second layer Karst caves and below is almost 0. The bending moment at the soil-rock interface is the largest， and the section is the most dangerous. The soil resistance p-depth z curve is a “convex belly” type. 3） As the number of Karst caves increases， the higher the location， the easier the p-y curve converges. The p-y curve for the soil section can be fitted using p/pub=α（y/y50）β. The influence of the number of Karst caves has little effect on the range of α and β values. The range of α and β values reflects the sensitivity of the p-y curve with depth and the sensitivity of both increases with the number of Karst caves. 4） To improve the horizontal tensile capacity of the single pile， when engineering piles pierce Karst caves， it is recommended to use the grouting method to improve the upper geotechnical properties， increase the reinforcement rate of the pile body at the soil-rock interface， and embed the pile body into the upper Karst caves floor to a certain depth so as to prevent the foundation pile from bending damage at the soil-rock interface.