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.

Failure mechanism and safety control technology of a composite strata roadway in deep and soft rock masses:a case study

The construction of coal mines often encounters deep composite soft rock roadways,which is characterized by significant deformation and poor stability.To deeply study the failure mechanism and large deformation challenges of a composite strata roadway in deep and soft rock masses,a numerical model of 3DEC tetrahedral blocks was established based on the method of rock quality designation(RQD).The results showed that original support cannot prevent asymmetric failure and large deformation due to the adverse geological environment and unsuitable support design.According to the failure characteristics,a coupling support of“NPR bolt/cable+mesh+shotcrete+steel pipe”was proposed to control the stability of the surrounding rock.The excellent mechanical properties of large deformation(approximately 400 mm)and high constant resistance force(bolt with 180 k N;cable with 350 k N)were evaluated by the tensile tests.The numerical results showed that the maximum deformation was minimized to 243 mm,and the bearing capacity of the surrounding rock of the roadway was enhanced.The field test results showed that the maximum deformation of the surrounding rock was 210 mm,and the forces of the NPR bolt and cable were stable at approximately 180 k N and 350 k N,respectively.This demonstrated the effectiveness of the coupling support with the NPR bolt and cable,which could be a guiding significance for the safety control of large deformation and failure in deep composite soft rock roadways.

Excavation-induced microseismicity and rockburst occurrence:Similarities and differences between deep parallel tunnels with alternating soft-hard strata

Excavation-induced microseismicity and rockburst occurrence in deep underground projects provide invaluable information that can be used to warn rockburst occurrence,facilitate rockburst mitigation procedures,and analyze the mechanisms responsible for their occurrence.Based on the deep parallel tunnels with the maximum depth of 1890 m created as part of the Neelum–Jhelum hydropower project in Pakistan,similarities and differences on excavation-induced microseismicity and rockburst occurrence between parallel tunnels with soft and hard alternant strata are studied.Results show that a large number of microseismic(MS)events occurred in each of the parallel tunnels during excavation.Rockbursts occurred most frequently in certain local sections of the two tunnels.Significant differences are found in the excavation-induced microseismicity(spatial distribution and number of MS events,distribution of MS energy,and pattern of microseismicity variation)and rockbursts characteristics(the number and the spatial distribution)between the parallel tunnels.Attempting to predict the microseismicity and rockburst intensities likely to be encountered in subsequent tunnel based on the activity encountered when the parallel tunnel was previously excavated will not be an easy or accurate procedure in deep tunnel projects involving complex lithological conditions.

Study on strata control by delay grouting in soft rock roadway

The properties of broken rock before and after grouting reinforcement are studied. Testing results show that grouting can raise the residual strength of broken rock, and the broken rockness by grouting can keep the steady supporting capacity within a relatively large deformation range. Revealing of the characteristics of stage deformation and damage process comes to the conclusion that the supporting of soft rock roadway should be analyzed in a dynamic view, and the grouting should be delayed at a proper occasion. Based on the above, the stepwise reinforcement technology characterized by immediate shotcreting, timely bolting and delay grouting is put forward and illustrated with a successful engineering practice.

Plastic zone analysis and support optimization of shallow roadway with weakly cemented soft strata

Based on a shallow roadway with weakly cemented soft strata in western China, this paper studies the range and degree of plastic zones in soft strata roadways with weak cementation. Geological radars were used to monitor the loose range and level of surrounding rocks. A mechanical model of weakly cemented roadway was established, including granular material based on the measured results. The model was then used to determine the plastic zone radium. The predicted results agree well with measured results which provide valuable theoretical references for the analysis of surrounding rock stability and support reinforcing design of weakly cemented roadways. Finally, a combined supporting scheme of whole section bolting and grouting was proposed based on the original supporting scheme. It is proved that this support plan can effectively control the deformation and plastic zone expansion of the roadway surrounding rock and thus ensure the long-term stable and safe mining.

上软下硬复合地层盾构隧道开挖面稳定性分析

针对上软下硬复合地层条件下盾构隧道开挖面的稳定性问题,依托深惠城际2标实际工况,分析不同软硬比及土体参数对开挖面极限支护压力的影响。利用颗粒流数值模拟分析土体的失稳模式,借助极限分析法建立符合开挖面失稳轮廓的理论计算模型,将理论计算结果与既往文献及实际工程进行比较分析。结果表明:当隧道开挖面主动失稳时,变形主要集中在软土层,硬岩层的变形较少;随着开挖面软硬比的增大,隧道开挖面的极限支护压力也增大;开挖面的极限支护压力与隧道埋深比无关,与土体内摩擦角成反比。

青川刨地里地震滑坡发育特征及其成因机制探讨

以“5·12”汶川地震诱发的青川县刨地里滑坡为例,现场调查了滑坡的地质特征,并基于离散元软件(UDEC)分析了1号滑坡动力响应及变形破坏过程,探讨了滑坡的成因机制。现场调查表明,刨地里1号滑坡具有近水平“上硬下软”的地层结构,其中石坎断层穿过了滑坡后缘;滑坡堆积体的岩性分带特征表明,刨地里1号滑坡下部千枚岩先于上部硅质岩被破坏,且破坏时间早于2号和3号滑坡;数值模拟研究揭示,峰值加速度放大效应在断层带附近的千枚岩内最强,其放大系数达6.79,导致下层千枚岩首先沿陡倾面产生拉裂破坏,随后上层硅质岩体产生拉裂破坏,结果与现场调查堆积物特征较吻合;断层和上硬下软的地层结构对刨地里滑坡动力响应、变形及破坏起到了控制作用。该研究可为上硬下软且含断层的地震滑坡的评价提供参考。

上软下硬复合地层盾构渣土改良试验研究

土压平衡盾构穿越上软下硬复合地层时存在刀盘“结泥饼”、排渣不畅和刀具磨损等难题。针对以上问题,以粉质黏土-全风化花岗岩复合地层为研究对象,基于渣土改良剂的地层适应性和性能测试开展不同地层渣土改良室内试验。研究泡沫剂和膨润土泥浆等渣土改良剂及其改良方法对上软下硬地层的改良效果,以获得土压平衡盾构在复合地层中的渣土改良方案及改良剂合理添加比。结果表明:(1)采用浓度为3%的泡沫剂溶液和配合比1∶8的膨润土泥浆进行联合改良可获得良好效果;(2)粉质黏土地层采用泡沫剂进行改良,渣土坍落度随泡沫添加比增加而增大,抗剪强度、黏聚力、内摩擦角和渗透系数随之减小,改良剂合理添加比为19.7%~22.8%;(3)全风化花岗岩地层采用泡沫剂和膨润土泥浆进行联合改良,可有效改善渣土流塑性和抗渗性,当采用全泡沫改良时,合理添加比为22.2%~28.7%,当采用泡沫与膨润土泥浆联合改良时,合理添加比为24.3%~31.5%。现场应用及施工效果反馈表明,采用以上改良方案可有效改善渣土流塑性,盾构推力、刀盘扭矩以及刀具磨损均有显著改善。

软硬地层接触面倾角对盾构隧道纵向力学性能的影响

针对现有盾构隧道纵向力学性能研究中较少考虑纵向穿越软硬变化地层,且接触面倾角影响规律尚不清晰的问题,基于实际工程建立盾构隧道-地层三维纵向精细化模型,并提出一种同时考虑管片错缝拼装、纵环向螺栓、地层与隧道接触面真实力学性能的精细化模拟方法;采用改进的Timoshenko梁理论验证模型可靠性,并分析穿越软硬变化地层盾构隧道的纵向力学性能,探讨地层接触面倾角的影响规律。结果表明:盾构隧道沉降量在软硬地层接触面急剧变化并在软硬地层两端趋于稳定,隧道两侧沉降差异在倾角为30°和150°时更为显著;管片张开和错台量集中分布于软硬地层接触面附近,分布范围随倾角增大逐渐向软土层侧移动,最大管片张开和错台量在倾角120°时最大,分别为0.183和1.270 mm;倾角对盾构隧道纵向内力影响较大,大于90°后影响逐渐显著;纵向上,管片纵向螺栓和地层-隧道接触面的变形更为显著。研究结果可为进一步发展盾构隧道纵向分析方法和保障此类盾构隧道的安全运营提供参考。

上软下硬地层隧道盾构施工地表沉降影响因素及规律研究

为研究盾构隧道穿越上软下硬地层时,开挖面内不同土岩厚度比对地表沉降的影响,以贵阳轨道交通3号线某区间隧道为工程背景,保持隧道埋深和双线隧道间距不变,建立7种工况下的三维有限元模型,通过与实测数据对比分析得到沉降规律,并利用双线隧道的44组地表沉降数据,拟合出适用于当地复合地层的Peck分段公式。研究结果表明:从整体看,数值模拟的沉降曲线均为W形,地表最大沉降位于先行隧道上方;穿越红黏土层时地表更易受到扰动而产生不均匀沉降,随着土岩厚度比的减小,模拟曲线对称性增强,左右隧道的沉降差缩小,整体沉降值基本表现为减小趋势;总结土岩厚度比与修正系数的关系,图表显示Peck分段公式能较好地预测贵阳上软下硬地层的沉降规律。

上软下硬地层盾构开挖面稳定性计算模型

针对上软下硬地层失稳特点,在假定开挖面附近因土体失稳而由软硬地层分界线先向上诱发形成部分楔形体、再呈倒圆台状向地面发展的基础上,提出开挖面稳定性计算模型。先基于极限平衡法提出部分楔形体计算模型;再依据修正后的楔形体计算模型,分别计算上覆土压力和开挖面前方部分楔形体的受力;最后依托青岛地铁6号线某区间工程开展数值模拟,验证理论模型。结果表明:不同支护应力比条件下的土体变形范围有所差异,土体变形主要发生在开挖面前方和上方并呈泡状延伸;数值模拟得到的开挖面失稳形态基本符合理论计算模型的假定形状;理论计算得到该例盾构开挖面极限支护应力比为0.21,与数值模拟的误差率为5%;当开挖面支护力小于极限支护力时,上软下硬地层开挖面水平变形会突然迅速增大;开挖面附近的岩土体变形主要发生在上部软弱部分,最大水平位移出现在上部软土中心附近,开挖面上土体最大水平位移与开挖面上方地表最大竖向位移间的相关性较高,两者变形规律类似。

上软下硬复合地层基于衬砌结构弯矩最小化的隧道横断面优化设计

[目的]为有效防止隧道衬砌破损及渗漏水,对上软下硬复合地层隧道横断面进行衬砌结构弯矩最小化设计研究。[方法]根据复合地层隧道围岩压力特点及合理假设,提出软土-硬土及土-岩两类复合地层隧道衬砌结构荷载作用模式。基于最理想的零弯矩复合地层隧道优化思路,建立隧道横断面半结构力学模型,计算得出零弯矩隧道横断面合理轴线方程,以及复合地层分界线处及隧道横断面水平中线处直径解析表达式。简述了复合地层隧道横断面弯矩最小化设计流程。[结果及结论]软土-硬土隧道零弯矩横断面合理轴线呈梨形,土-岩隧道零弯矩横断面合理轴线呈类马蹄形;实际工程可基于隧道横断面合理轴线方程,通过综合评估和加权平均法来确定隧道横断面设计所需关键参数,从而设计出新型上软下硬地层隧道横断面,以期最大限度减少复合地层隧道横向变形。

上软下硬地层盾构下穿既有隧道扰动变形研究

针对上软下硬倾斜地层中,盾构下穿既有地铁时的管片变形控制问题,以武汉轨道交通7号线下穿既有2号线工程为背景,采用三维数值模拟方法和离散元软件3DEC建立地铁2号线管片模型,同时使用FLAC3D软件进行三维数值分析,探讨新建隧道与既有隧道间距、地层倾斜和注浆填充对既有地铁及周边地层的影响。分析结果表明:既有隧道沉降值受地层条件和隧道间距影响显著,尤其在新建盾构隧道与既有隧道距离较近时;既有地铁管片加固和新建隧道注浆填充对控制上软下硬地层条件下新建隧道近接下穿既有隧道的沉降变形具有显著效果。在新建盾构隧道施工前需对既有地铁管片的前期变形量进行准确分析,确保既有隧道安全,且加固和注浆填充措施对于类似工程的变形控制至关重要。

顺层偏压挤压性软岩隧道让压预留变形角支护技术研究

针对顺层偏压挤压性软岩隧道的非均匀大变形问题,提出一种基于钢拱架预留变形角的新型让压单元。基于三维精细化建模分析顺层偏压荷载下让压预留变形角支护的承载特性和效果,并应用于中老铁路甘庄隧道,验证新型让压预留变形角支护技术的可行性。研究结果表明:1)顺层偏压荷载下隧道支护结构以弯曲变形为主,传统让压柔性节点在弯矩内力作用下易发生受拉破坏,让压预留变形角能有效释放拱架的弯矩内力,适应更大的弯曲变形;2)顺层偏压荷载作用下,采用让压预留变形角的钢拱架整体应力水平明显降低,拱架整体的承载能力满足强度要求;3)工程现场采用局部扩挖和设置钢拱架让压预留变形角后,隧道变形在断面开挖18 d以后控制在允许范围内,初期支护的应力集中现象减弱,钢拱架主体不再发生弯曲破坏。

“三软地层”超前探放水综合控制技术

“三软地层”探放水钻孔孔口管固管安装困难、顶板遇水塌陷渗水、疏放水钻孔坍塌堵孔以及钻孔缩颈的施工技术一直难以解决。通过理论计算与工程实践,摸索了一套探放水创新施工工艺,进行了优化钻孔参数设计,11701工作面大部分顶板疏放水钻孔垂高取200 m,终孔孔距不大于60 m,富水区域进行加密。技术上攻克了套管加长后固结难的技术难题,研发出一套“分级注浆固管法”,将整个套管牢固安装在设计位置,实现了在软岩区域快速固结安装超长孔口套管的新工法。针对“三软地层”的钻孔探放水,为了解决“三软地层”的探放水钻孔在成孔后坍塌堵塞的技术难题,创造性的研发出三级注浆以及“全孔花管护壁新工艺”;工程实践证明该套技术方案很好地解决了“三软地层”探放水钻孔施工难题。

基于精细化数值模拟的地铁盾构隧道椭圆度安全研究

随着城市地铁运营里程不断增长,盾构隧道过量变形导致的结构安全问题持续出现。对出现过大变形的盾构隧道进行结构分析时,准确的岩土参数难以获取且外部因素十分复杂,在数值模拟中难以全面考虑。以可靠的实测数据作为精细化数值模拟分析的基础,更有利于还原当前的结构状态。因此,为更真实地通过数值模拟方法分析盾构隧道的结构安全状况,继而得出基于椭圆度的结构安全控制标准,提出以隧道椭圆度为基准,在保证隧道结构合理的受荷条件下使隧道变形结果与实际相近,结合某上软下硬地层中隧道变形过大的典型案例相互论证,从而进行盾构隧道的结构力学响应分析。研究结果表明:当隧道结构主要承受竖向对称荷载时,拱顶接头位置变形与螺栓应力最大;拱顶内侧易出现裂缝,拱腰接缝区域容易出现渗漏;管片椭圆度为0~10‰时,结构较安全;椭圆度在10%~20‰时,结构拱顶内侧开始出现塑性区;椭圆度在20%~30‰时,塑性区不断发展,拱顶螺栓接近进入屈服阶段;通过对比管片损伤、螺栓应力、接缝张开量等随椭圆度增加的变化,结合工程案例中的实际状况,并考虑为隧道结构变形保留适当冗余,可将该区间隧道基于椭圆度判断的变形标准的控制值设为25‰,预警值设为20‰。

上软下硬地层地铁盾构施工地表沉降模拟分析

为了研究上软下硬地层地铁盾构掘进引起的地表沉降规律,以某地铁工程大岭山东站—松山湖站区间盾构掘进项目为依托,通过实测和数值模拟,对比分析上软下硬地层盾构掘进及硬层比对地表沉降规律的影响。结果表明:单双线盾构掘进地表横向沉降规律分别呈V形和W形变化;盾构掘进时对前后地表变形影响的范围约为40 m,其中前方5 m至后方15 m范围内的地表沉降变化率最大;地表沉降随地质硬层比的增加逐渐减小,硬层比为16.7%~83.3%时,地表沉降变化较大,可将硬层比83.3%、16.7%作为上软下硬复合地层研究的上下限。

膨胀性软破岩层深竖井施工分级支护研究

境外某铜金矿千米深竖井在通过膨胀性软破岩层(泥灰岩)时,围岩遇水膨胀压力极大,先后出现两次井壁垮塌和开裂的情况,对施工进度及施工人员安全产生极大影响。为解决该问题,查找相关文献资料及国内外类似施工案例,对通过膨胀性软破岩层的井壁破裂机理进行分析,针对性地制定井壁破裂修复方案;在此基础上,进一步调查施工地点的工程地质和水文地质情况,通过分析与总结,提出深竖井不良岩层的施工及分级支护方案,对其所穿过的膨胀性软破岩层的围岩制定分级表,根据不同岩体等级分别提出相应的施工及具体支护方案。通过对两次破裂处井壁的修复,较长时间内未出现裂缝及漏水现象,修复效果良好,达到预期;此外,竖井井筒后续施工中在采用分级支护方案后,井筒顺利通过厚度超过500 m的不良岩层,且在工期、质量、安全三个方面都取得良好效果,保障该深竖井工程的施工质量与施工安全。该工程为膨胀性软破岩层中的深竖井掘进施工积累了宝贵经验,对类似工程具有一定的借鉴意义。

天津地区盾构施工同步注浆浆液地层适配性

针对天津地区典型软土地层盾构隧道工程,对同步注浆的单液活性浆液配比进行分析,通过层次分析法、熵值法分析得到浆液性能指标权重。结果表明:水胶比、膨水比对浆液稠度影响较大;水胶比、胶砂比对浆液凝结时间影响较大;水胶比、膨水比对浆液泌水率影响较大;水胶比对浆液抗压强度影响较大;水胶比和胶砂比对浆液固结收缩率影响较大。通过博弈论组合权重法分析发现浆液凝结时间、抗压强度的权重最高,密度权重最低。通过优劣解距离法对浆液进行筛选,得到了适用于天津软土地层的同步注浆浆液配比。为天津地区盾构隧道同步注浆浆液配比提供借鉴。

海洋自适应伸缩绳索取心钻探工艺研究及应用

海洋取心钻探钻遇软硬交互地层时,往往采取提钻更换相匹配的取心钻具来应对不同硬度的地层。海上作业成本高,频繁起下更换钻具耗费时间长,面对软硬交互地层工况,研发了自适应伸缩绳索取心钻探工艺。钻遇绵软地层时,内管超前伸出,由内管安装的钻头进行取心钻进;钻遇坚硬地层时,内管在地层对钻压的反力下会压缩其内部的弹簧从而回缩到钻具外总成当中,由外总成钻头进行取心钻进,在压缩弹簧的调解下,可根据地层硬度的变化自动调整取心钻进方式。通过工程应用检测,使用该工艺平均岩心采取率高,达到了保证取心质量、延长内管钻头工作寿命的目的,提高了作业效率和安全性,为海洋工程勘察提供了借鉴。