岩溶地区某33层住宅楼桩端基岩厚度不足问题分析及处理

Analysis and treatment of insufficient pile-end bedrock thickness of a 33-storey residential building in karst area

结合某33层住宅桩端基岩厚度小于3d和5m这一问题,详细分析了其产生原因及处理方法。其原因为:基岩面倾斜、超前钻或桩基的倾斜导致超前钻见岩标高与桩基全断面见岩标高相差较大,且未重新进行补钻;或桩端3d和5m以内有溶洞,但超前钻擦溶洞边而过从而未能发现溶洞。其处理方法是:利用桩基承载力计算没有计入侧阻力、大多数桩承载力未用足等有利因素,结合不同位置的溶洞对桩承载力影响程度的不同进行综合分析,从而减少处理数量;当必须处理时,可采用'高压注浆置换溶洞充填物'的方法处理,也可采用'新增桩基+托换梁'的方法处理。

The pile-end bedrock thickness of a 33-storey residential building was less than 5 m and 3 times of pile diameter.The causes and treatment methods for this problem were analyzed in detail.There were two main reasons.First,bedrock surface inclination,advance drilling or pile foundation inclination led to the great difference between rock elevation of advanced drilling and rock elevation of full cross-section pile foundation,and no additional drilling was carried out when this problem was identified.Second,there were karst caves within distance of 5 m and 3 times of pile diameter from the pile end,but karst caves was not found because advanced drilling might brush against the edge of karst caves.The treatment methods were as follows.Some favorable factors could be manipulated such as side resistance not taken into consideration in the calculation of bearing capacity of pile foundation and the bearing capacity of most piles not used fully,and comprehensive analysis was carried out according to the different influences of karst caves at different locations on pile bearing capacity,thus reducing the number of treatments.When the problem had to be dealt with,the method of'replacing karst cave fillings with high-pressure grouting'or the method of'adding pile foundation+underpinned beam'could also be used.