旁孔透射波法检测桩长的影响因素及修正方法探讨

Discussion on Influence Factors and Correction Method of Pile Length Detection by Side Hole Transmission Method

旁孔透射波法检测桩长已经有多年的应用,理论上是通过识别深度(Z)-时间(t)关系图形的拐点来确定桩底所在的深度。目前对桩长的判定一般有三种方法,即交点法、平移法、校正法,由于受各种因素影响,尤其受桩周地层波速变化的影响,三种方法对桩长判定都存在着很大的误差。本文从桩长判定影响因素分析入手,从五个方面分析了旁孔透射法检测桩长的影响因素,并经过正演推算及实践,给出一种新的桩长判定方法:实测地层波速修正法。根据对钻孔地层波速实际测量,对桩孔之间土层的纵波走时进行修正,以达到更精确判定桩长的目的。最后分别从实测地层波速修正法计算模型和实例两个方面分析讨论了实测地层波速修正法的可行性和准确性,结果表明实测地层波速修正法能够大幅度提高桩长判定的准确度,是一种全新合理的旁孔透射判定桩长的方法。

The side hole transmission method has been widely used for many years in detecting the pile length.In theory,the depth of the pile bottom is identified by the inflection point of the depth(Z)and the time(T)relationship graph.At present,among the three methods detecting the pile length,whether intersection method,translation method or correction method,errors occur frequently.Based on the interpretation of the influencing factors of pile length determination,this paper analyzes the influencing factors of pile length detection by side hole projection method from five aspects.Based on forward calculation and work practice,the author propose a new method of pile length determination:wave velocity correction method of measured stratum.According to the actual measurement of the wave velocity of the borehole stratum,the longitudinal wave travel time of the soil layer between the pile holes is corrected to achieve the purpose of more accurate determination of the pile length.Finally,the feasibility and accuracy of the wave velocity correction method are analyzed from the calculation model and examples of the measured formation wave velocity correction method.The results show that the wave velocity correction method can greatly improve the accuracy of pile length determination,indicating it is a new and effective method to determine the pile length by side hole projection.