断层对地应力场方向的扰动规律及反演分析方法

Disturbance law of faults to in-situ stress field directions and its inversion analysis method

地下工程区的断层对局部应力场的方向有着复杂的影响。为准确获取断层扰动下的初始应力场,提出基于等效构造作用荷载的二次反演分析方法。首先,通过定性认识和简单数值试验分析断层附近主应力方向的偏转规律,可为识别受断层影响的异常实测应力数据提供判断依据。其次,主要考虑河谷地形的影响,采用改进的侧压力系数法反演大模型应力场。然后,建立含断层的精细化小模型,并根据在大模型中插值获取的应力场来计算等效构造作用荷载,基于弹塑性理论进行应力场的二次反演计算。最后,针对金川地下厂房地应力实测资料反演初始应力场,验证了3#测点的异常是受断层扰动影响,并研究断层附近的应力场规律。研究结果表明:局部应力场方向在断层带内外的偏转规律不同,且跟断层产状有显著关系;反演方法能综合考虑河谷地形、断层、复杂构造作用的影响,对实测点的反演精度高,能较好地反映断层附近应力场量值和方向的不均匀特性。

Faults in underground engineering areas have complex influences on the direction of local stress field. In order to accurately obtain the distribution of in-situ stress field due to fault disturbance,a two-stage inversion analysis method based on equivalent tectonic load is presented. Firstly,based on qualitative cognition and a simple numerical experiment,the deflection laws of the principle stress direction near a fault are analyzed for providing a judgment basis of identifying the abnormal measured stress data affected by the fault. Secondly,mainly considering the influence of valley topography,the improved lateral pressure coefficient method is applied to invert the in-situ stress field of big model,and then,a refined small model with faults is built. The equivalent tectonic load is obtained by the stress field calculated by interpolation from the big model,and the second-stage inversion calculation for in-situ stress is conducted based on elastic-plastic theory. Finally,the in-situ stress field of Jinchuan underground powerhouse area is inverted based on the measured in-situ stress data,verifying that the abnormal data at point #3 are affected by the fault,and the distribution laws of the stress field near the faults are studied. The results indicate that the local stress field direction deflects differently inside and outside the fault and has a significant relationship with the occurrence of the fault. The inversion method can comprehensively consider the influences of valley topography,fault and complex tectonism,has a high inversion accuracy to measured data and can better reflect the non-uniform characteristics of stress magnitude and direction near faults.