灌注桩钢筋笼外部的磁异常特征研究
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摘要
灌注桩中的钢筋笼在地磁场中受磁化作用而产生磁感应强度,使灌注桩附近的磁场强度发生变化.通过分析水平磁性圆柱体外部的磁异常特征,结合模型桩试验,研究了灌注桩钢筋笼外部的磁异常特征,结果表明在钢筋笼外侧钻孔中的磁异常总体上呈现"两峰夹一谷"的特征,钢筋笼中部呈宽缓的马鞍形负异常,钢筋笼底端位置对应磁异常从极小值转变为极大值的拐点.研究成果从理论上为用磁测井法检测灌注桩中钢筋笼长度奠定了基础.
Steel bars in cast-in-situ pile will be magnetized under the excitation of geomagnetic field,which changes the magnetic field around pile.Based on the magnetic anomaly characteristics out of a horizontal cylinder and the results of model piles test,the magnetic anomaly characteristics out of reinforcement cage in cast-in-situ pile were analyzed.The analysis results indicate that the magnetic anomaly curve along the borehole depth out of reinforcement cage has a form of 'a valley between two peaks',on which a wide negative anomaly region like a saddle corresponds to the middle part of reinforcement cage and an inflexion from minimum to maximum corresponds to the bottom of reinforcement cage.It provides a basis for the length detection of reinforcement cage in cast-in-situ pile.
Steel bars in cast-in-situ pile will be magnetized under the excitation of geomagnetic field,which changes the magnetic field around pile.Based on the magnetic anomaly characteristics out of a horizontal cylinder and the results of model piles test,the magnetic anomaly characteristics out of reinforcement cage in cast-in-situ pile were analyzed.The analysis results indicate that the magnetic anomaly curve along the borehole depth out of reinforcement cage has a form of 'a valley between two peaks',on which a wide negative anomaly region like a saddle corresponds to the middle part of reinforcement cage and an inflexion from minimum to maximum corresponds to the bottom of reinforcement cage.It provides a basis for the length detection of reinforcement cage in cast-in-situ pile.
引文
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[3]涂广红,江为为,朱东英,等.中国东北地区剩余重磁异常特征与地质构造及成矿带的关系[J].地球物理学进展,2006,21(3):746~755.
[4]长春地质学院磁法教研室.磁法勘探[M].北京:地质出版社,1979,12~15、145~150、228~230.
[5]王亶文.二十世纪的地球偶极子磁场[J].地球物理学报,2005,48(1):52~55.
[6]高金田,安振昌,顾左文,韩炜,詹志佳,姚同起.地磁正常场的选取与地磁异常场的计算[J].地球物理学报,2005,48(1):56~62.
[7]成都地质学院物探系.磁法勘探[M].北京:地质出版社,1976,27~29.
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