断层分支作为主断层的一部分普遍存在，不易引起人们重视，但断层分支是引起突水的主要因素之一。

以安徽刘庄煤矿为工程地质背景，在考虑Mohr-Coulomb准则岩体压剪断裂判据基础上，建立断层分支渗流与应力双重影响下的断裂力学灾变模型，分析得出断层分支发生劈裂破坏时的临界水压及断层分支到底板破碎区最小安全距离，研究断层倾角、最小主应力、主断层长度和渗透水压对临界水压及最小安全距离的影响规律和主控影响因素，并模拟分析断层分支在采动影响下塑性区及渗流场的演化特征，开展现场压水试验的验证工作。

结果表明：(1)断层分支倾角越大越易发生突水；最小主应力越大，断层分支裂隙越不容易发生扩展；(2)当主断层倾角为60°且断层分支与主断层夹角为60°时，模拟分析结果显示在工作面推进至断层分支正上方位置时，断层导升通道整体活化贯通；当工作面推过断层分支正上方10 m后，断层分支尖端裂隙与工作面底板破坏带贯通并引起底板突水；(3)通过现场压水试验验证了理论计算的正确性，证实断层分支会造成底板裂隙提前与断层相互贯通，引起工作面出水。研究结果可为煤矿采场底板含此类断层分支时的防水煤柱留设提供一定参考。

Despite wide distribution, the branches of major faults (also referred to as the fault branches) tend to be overlooked. However, they represent one of the primary causes of water inrush.

Under the engineering geological background of the Liuzhuang coal mine in Anhui Province, this study established a fracture mechanical disaster model for fault branches under the impacts of both seepage and stress based on the criteria for compression-shear fracture of rock masses considering the Mohr-Coulomb criterion. Using this model, this study obtained the critical water pressure and the minimum safe distance between the fault branch and the floor's fractured zone in the case of fault branch splitting. It investigated the influence patterns of factors including the fault dip angle, minimum principal stress, length of a major fault, and seepage water pressure on critical water pressure and the minimum safe distance, determining the dominant influencing factors. Furthermore, this study simulated the evolutionary characteristics of the plastic zones and seepage fields of the fault branches under the mining effects and verified the results using in-situ water pressure tests.

Key findings are as follows: (1) A higher dip angles of the fault branches corresponded to a higher susceptibility to water inrushes, while a higher minimum principal stress suggested a lower probability of the fissure propagation of the fault branches. (2) In the case where the dip angle of the major fault and the angles between the fault branches and the major fault were both 60°, fault channels were entirely activated and connected when the mining face advanced directly above the fault branch, as indicated by the simulation results. After the mining face advanced 10 m away from the fault branches, fissures at the tip of the fault branches were connected to the fractured zone of the mining face’s floor, resulting in water inrushes from the floor. (3) The in-situ water pressure tests verified the correctness of theoretical calculations, proving that fault branches can cause early interconnection between fissures on the floor and faults, leading to water outflow from the mining face. Overall, the findings of this study provide a reference for setting up waterproof coal pillars in coal mines with Y-shaped fault branches on stope floors.