灰岩区溶洞与薄层泥岩物探异常差异分析

针对地球物理反演问题存在多解性、单一物探解译成果易与实际情况产生偏差等问题,以区分灰岩区大型溶洞与岩体破碎产生的相似TSP异常、提高超前预报解译精度为目标,将EH4、TSP303及地质雷达技术用于千岛湖配水工程灰岩区不良地质探测。简述了三种物探方法的原理及观测系统设置方式在EH4电磁异常区域开展隧洞超前预报工作,物探成果有效揭示了不良地质的存在。鉴于TSP两次预报异常相似但开挖结果不同,提出了根据TSP纵波速度谱中低速带的分布形态来区分溶洞与破碎岩体的方法。结果表明:大型溶腔与薄层泥岩均对应偏低的纵波波速、密度及杨氏模量,但前者在TSP纵波速度谱中表现为小范围封闭状低速异常,后者低速带呈带状,产状相对清晰;溶洞雷达异常表现为双曲线状同相轴且具备与完整灰岩对比度明显的强振幅特性,薄层泥岩反射能量较溶腔弱,波形杂乱错断,但未呈现明显双曲线特征。

Analysis on abnormal difference of geophysical prospecting between karst cave and thin layer mudstone in limestone region

Aiming at the problems of the ambiguity of the geophysical inversion，the result of single geophysical interpretation being prone to be deviated with that of the actual situation，etc. ，the techniques of EH4，TSP303 and georada are applied to the prospecting of the poor geology in the limestone region of Thousand Island Lake-Hangzhou Water Transfer Project by taking distinguishing the abnormity of similar TSP caused by rock mass breaking from the large scale karst cave and enhancing the interpretation accuracy of the advanced prediction as the objectives. The principles and layout of the observation systems of three geophysical prospecting methods applied to the advanced geological predictions of tunnel within the EH4 electromagnetic abnormal zone are briefly described herein，from which the existences of poor geological conditions are effectively revealed from the geophysical prospecting results. Considering that the abnormities from two times of TSP predictions are similar，but the results from the excavations are different，the method to distinguish karst cave from broken rock mass with the distribution pattern of the mid-low velocity zone in the TSP longitudinal wave velocity spectrum is put forward. The result shows that both large-scale karst cave and thin layer mudstone are corresponded to lower longitudinal wave velocity，density and Young's modulus，but the former presents the abnormity of the small range closed low velocity in the TSP longitudinal wave velocity spectrum，while the low-velocity zone of the latter presents a zonal type with a relative clear occurrence. The radar anomalies of karst cave have strong amplitude characteristics of hyperbolic shaped sync-phase axis and clear contrast with intact limestone，while the reflecting energy of the thin layer mudstone is weaker than that from karst cave with disordered and broken wave-shapes，but no significant hyperbolic characteristics are presented therein.