Influence of confined water on the limit support pressure of tunnel face in weakly water-rich strata

In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.

断层破碎带突水突泥演化特征试验研究

为了研究富水断层破碎带隧道突水突泥灾害演化机制,自行研制了一套可考虑质量迁移及地应力状态的大型室内突水突泥试验系统。利用该装置开展了不同水压加载方式、不同破碎带介质参数等条件的断层破碎带突水突泥灾害演化过程模拟试验。结果表明:(1)断层破碎带突水突泥灾害演化是渗流-侵蚀强耦合过程,在水压作用下,破碎带介质中的细颗粒首先发生迁移,导致充填介质孔隙结构增加,进而加速细颗粒流失,促使涌水率不断增长,随着细颗粒不断迁移流失,水流流态由层流转换为紊流,最终诱发突水突泥灾害;(2)破碎带介质初始孔隙率和施加水压越大越易诱发突水突泥,介质渗流演化特征越明显,渗流场参量如渗透率、孔隙率、雷诺数增加越快,且渗流场参量演化曲线出现突增现象;(3)梯度水压加载模式下断层破碎带介质较恒定水压加载条件下突水突泥演化特征更明显,介质发生突水突泥的临界水压更小。在此基础上,基于涌水率-时间(Q-t)、水力梯度-涌水率(i-Q)关系的流态转换分析和基于渗透率-水力梯度(k-i)关系的渗透性演化特征,建立了断层破碎带渗透演化特征概化模型。该研究结果对于断层破碎带突水突泥灾害演化机制与防治措施具有一定的理论指导价值。

新型水玻璃-酯类注浆材料及其固沙体特性研究

针对风积沙边坡稳定性差和常用加固技术存在成孔困难、加固范围有限等问题,提出以二元酸酯为固化剂的新型水玻璃-酯类浆液对风积沙进行加固的思路。采用倒杯法和旋转黏度计对新型水玻璃-酯类浆液的凝胶时间、黏度时变性进行了系统测试,并通过三轴试验研究不同浆液填充率对固沙体强度和渗透性的影响规律。研究表明:新型水玻璃-酯类浆液凝胶时间在20 s^60 min之间,浆液黏度随时间增长呈现指数型增长变化,且凝胶之前黏度低;当浆液填充率从0%增加至100%,固沙体黏聚力由0kPa线性增加至148.4 kPa,内摩擦角按抛物线变化规律从32.1°增加至37.8°,渗透系数从3.42×10^-5 cm/s降低到8.74×10^-7 cm/s;与水玻璃-磷酸浆液、水玻璃-硫酸浆液相比,新型水玻璃-酯类浆液固沙体抗压强度高。该研究结果为风积沙边坡加固提供了新的方法。

纤维硅灰水泥石强度与浆液抗冲刷特性

针对隧道突水灾害防治对注浆材料的特殊要求,在水泥浆中加入外掺剂改善其力学特性与抗冲刷特性。通过测试不同水灰比、纤维掺量、硅灰掺量下水泥石的抗压与抗折强度,得出各水灰比下的强度最佳配合比,并测试最佳配合比下浆液的流动性与抗冲刷特性。试验发现,纤维与硅灰的掺入能够显著提高水泥石的强度,且对浆液的流动度影响不大;低流速下纤维硅灰水泥浆的抗冲刷特性较纯水泥浆改善显著,但流速较高时其抗冲刷特性仍较差。基于此,在纤维硅灰水泥浆中再掺入可再分散性乳胶粉进一步改善浆液抗冲刷特性。试验结果表明,可再分散性乳胶粉能明显改善浆液抗冲刷特性,即使在较高流速(0.6 m/s)下,其浆液留存率仍达到60%以上。研究结果为隧道突水灾害防治与动水注浆浆液选择提供了参考。

Evaluation of mountain slope stability considering the impact of geological interfaces using discrete fractures model

The stability of rock slope is often controlled by the existing discontinuous surfaces, such as discrete fractures, which are ubiquitously distributing in a geological medium. In contrast with the traditional approaches used in soil slope with a continuous assumption, the simulation methods of jointed rock slope are different from that of in soil slope. This paper presents a study on jointed rock slope stability using the proposed discontinuous approach, which considers the effects of discrete fractures. Comparing with traditional methods to model fractures in an implicit way, the presented approach provides a method to simulate fractures in an explicit way, where grids between rock matrix and fractures are independent. To complete geometric components generation and mesh partition for the model, the corresponding algorithms were devised. To evaluate the stability state of rock slope quantitatively, the strength reduction method was integrated into our analysis framework. A benchmark example was used to verify the validation of the approach. A jointed rock slope, which contains natural fractures, was selected as a case study and was simulated regarding the workflow of our framework. It was set up in the light of the geological condition of the site. Slope stability was evaluated under different loading conditions with various fracture patterns. Numerical results show that fractures have significant contributions to slope stability, and different fracture patterns would lead to different shapes of the slip surface. The devised method has the ability to calculate a non-circular slip surface, which is different from a circular slip surface obtained by classical methods.

Formation mechanisms of water inrush and mud burst in a migmatite tunnel：a case study in China

This paper presents a case study of water inrush and mud burst occurring in a migmatite tunnel to study its formation mechanisms. The geological investigation and mineralogical analysis showed that water inrush and mud burst in the migmatite was closely related to the component of the host rock. High content of soluble minerals,e.g.,calcite and dolomite,would make the migmatite rock prone to be fragmentized,isintegrated and eventually form different sorts of connected or semi-connected veins. The field exploration revealed most cavities in the magmatite tunnel were eroded by groundwater and formed large interconnected networks. The two faults and the dike in the magmatite tunnel became the preferred paths and provided great convenience for plenty of precipitation and mud slurry. Due to high water pressure and blast disturbance,the cavities can soon connect each other as well as all sorts of veins,forming a complex ground channel for water inrush and mud burst. To estimate the potential occurrenceof water inrush and mud burst,the water bursting coefficient was employed. The results showed the water bursting coefficient of the magmatite tunnel was much bigger than the threshold values and it can be used to explain the accident of water inrush and mud burst occurring in the magmatite tunnel.

考虑质量迁移的全风化花岗岩隧道突水突泥试验

为研究全风化花岗岩隧道突水突泥变质量渗流特征及灾害演化机理,自行设计了一套可考虑质量迁移及三向应力状态的大型室内突水突泥试验系统。该试验系统主要由加载系统、渗流系统、泥水回收系统组成,具备模拟地层三向应力状态的特点,且设计的渗流系统能较好地模拟颗粒迁移特性。利用该装置系统开展不同水压力及围压下的突水突泥演化试验。结果表明:①全风化花岗岩隧道突水突泥灾害演化是渗流-侵蚀强耦合过程,岩体颗粒在水力作用下发生侵蚀流失,致使岩体孔隙、渗透率增长,进而再次加快颗粒迁移,促使涌水量不断增长;同时,随颗粒物不断迁移,水流流态可能由线性流向非线性流发生突变,最终诱发突水突泥灾害。即,颗粒迁移是突水突泥演化的内因,水流流态的转换是灾变的关键;②突水突泥灾变风险随水压力增加而增加,特别是当水压力达到0.6 MPa时,颗粒流失量达到总质量的11%,涌水量更达到395.84 mL·min^(-1),是低压力(0.4 MPa)条件下的4.3倍,且水流流态也由线性流向非线性流转变,表明存在临界水压力促使灾害发生;③突水突泥灾害演化随围压加大而逐步加快,尤其是对灾害演化的初始阶段,表征围压的增长显著加快灾害的初始演化速率并缩减灾害预防时间,因此在高围压环境下须重点监测初期的渗流侵蚀特性。

新型水玻璃-酯类浆液对风积沙边坡稳定性研究

针对风积沙边坡稳定性差的问题,在新型水玻璃-酯类浆液性质研究的基础上,采用新型水玻璃-酯类浆液对风积沙边坡进行加固,并通过数值模拟的方法研究新型水玻璃-酯类浆液填充率和加固深度对桥台开挖工况下风积沙边坡稳定性的影响。研究结果表明,天然状态下风积沙边坡安全系数为1.15,滑动面近似平行于坡面。在未对风积沙边坡进行加固时,桥台开挖后风积沙边坡最大水平位移为30.6cm,塑性区通过桥台开挖形成的转角处,安全系数为1.03、低于天然状态下的1.15,说明在未加固的条件下对风积沙边坡进行桥台开挖会极大降低风积沙边坡稳定性。新型水玻璃-酯类浆液填充率和加固深度对桥台开挖状态下风积沙边坡稳定性影响结果表明,随着浆液填充率和加固深度的增加,风积沙边坡安全系数不断增加。