基于实测地震波波速的围岩各向异性分析——以赣龙铁路汀州隧道为例

Analysis of surrounding rock anisotropy based on measured seismic wave velocity——A case study of Tingzhou Tunnel in Ganzhou-Longyan Railway

在赣龙铁路汀州隧道地震波反射法超前地质预报的基础上,选取地震波记录较好的57次测试成果,通过地震波激发炮孔段围岩水平、竖直方向横波波速差异性的统计分析,对围岩的各向异性进行研究。数据分析表明：围岩水平和竖直方向的横波波速不同,表现出不同程度的横波各向异性;赣龙铁路汀州隧道围岩总体上表现出竖直方向的横波波速高于水平方向的各向异性特点,围岩横波各向异性系数绝大部分在±10%以内,动弹性模量、动剪切模量、动泊松比各向异性系数的分布范围分别为-15%-15%、-20%-20%和-20%-15%;围岩的各向异性程度与围岩级别、地震波纵波波速和隧道埋深有较密切的关系;当围岩的地震波纵波波速在3 800-5 000 m/s之间或隧道埋深在60-100 m之间时,横波各向异性系数离散程度较大;在测试的Ⅱ~Ⅴ级围岩中,Ⅳ级围岩的横波各向异性离散程度最高,Ⅱ级围岩的最低。

Based on the advanced geology forecast by seismic reflection method at Tingzhou Tunnel in Ganzhou-Longyan Railway, fifty-seven selected seismic records are used for investigation. Within the segments of excited seismic wave in the surrounding rock, the differences of the shear wave velocity in horizontal and vertical directions are analyzed statistically, separately. Additionally, the anisotropy of surrounding rock is also considered. It can be seen from the results that when the shear wave velocities in horizontal direction vary from in vertical direction, shear wave anisotropy presences in different degrees in the surrounding rock. Vertical shear wave velocities are generally higher than the horizontal ones, and the most of shear wave anisotropy coefficients are within 4-10%. It is found that the anisotropy coefficients of dynamic elastic modulus, dynamic shear modulus and dynamic Poisson ratio are in the ranges from -15% to 15%, from -20% to 20%, from -20% to 15%, respectively. The anisotropy degree of surrounding rock depends on the grade of surrounding rock, seismic longitudinal wave velocity and the buried depth of tunnel. The anisotropy coefficient of shear wave and its discrete degree are relatively higher, when the seismic longitudinal wave velocities are between 3 800 and 5 000 meters per second or when the buffed depth of tunnel is between 60 and 100 meters. Among the tests conducted on the surrounding rock of grades Ⅱ-Ⅴ, it is noted that the shear wave anisotropy and its discrete degree is the highest in surrounding rock of grade Ⅳ, but is the lowest in the surrounding rock of grade Ⅱ.