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.

Pseudo-dynamic analysis of a 3D tunnel face in inclined weak strata

A new discretization technique is proposed for a three-dimensional(3D)tunnel face in weak strata with a random position in space.This method limits the angle,height,and thickness of the strata on the tunnel face.The original whole piece of soil is separated by a series of parallel planes,and two parallel planes are used as a stratum.Each radial discrete plane is separated when it passes through the strata,and the change in the soil properties of discrete points on the truncated plane is considered separately inside the strata.Considering the spatial and temporal characteristics of seismic waves,a pseudo-dynamic analysis of the tunnel face is carried out.The tunnel face active damage types under earthquake conditions are quantitatively analyzed,and the corresponding support pressure design diagrams are given for the case without weak strata.For the case containing weak strata,the presence of weak strata can have adverse effects on the face.The failure mechanism of the weak strata is given by the discretization method.For different friction angles,the presence of the weak strata changes the friction angles of the soils.For the thickness,location and angle of the weak strata,the variation in the support pressure is given in this paper.To more intuitively depict the change in the failure mechanism in the presence of weak strata,the change in the failure mechanism under different thicknesses and weaknesses of weak strata is plotted.

Time-dependent safety of lining structures of circular tunnels in weak rock strata

Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.

Support technology for mine roadways in extreme weakly cemented strata and its application

For the engineering geology conditions of bad mine roadway roof and floor lithology in extremely weak cemented strata, the best section shape of the roadway is determined from the study of tunnel surrounding rock displacement, plastic zone and stress distribution in rectangular, circle arch and arch wall sections, respectively. Based on the mining depth and thickness of the coal seam, roadway support technology solutions with different buried depth and thickness of coal seam are proposed. Support schemes are amended and optimized in time through monitoring data of the deformation of roadway, roof separation, l-beam bracket, bolt and anchor cable force to ensure the long-term stability and security of the roadway surrounding rock and support structure. The monitoring results show that mine roadway support schemes for different buried depth and section can be adapted to the characteristics of ground pressure and deformation of the surrounding rock in different depth well, effectively control the roadway surrounding rock deformation and the floor heave and guarantee the safety of construction and basic stability of surrounding rock and support structure.

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.

采动力学与岩层控制关键理论及工程应用

研究岩体采动力学响应和岩层控制技术对促进煤炭安全高效开采、保障能源稳定供给具有重要意义,是实现煤炭资源科学开采的理论基础。矿山岩体灾害(围岩变形、冲击地压等)频发,其形成-演化-发生全过程与采动力演化分布、岩层运动、开采扰动和能量演化密切相关。基于实用矿山压力控制理论,提出并阐述了采场岩层控制进展与控制准则,建立了定量分析的力学模型和设计方法,发展了针对性的岩体灾害控制技术,并创新研制了配套试验研究装备。采动力学与岩层控制理论将岩层控制分为采场岩层控制和巷道围岩控制;提出控制或利用采动岩层运动改变致灾条件,给出“给定变形”和“限定变形”准则;调控“3S”因素准则(围岩应力环境、围岩结构属性、围岩支护结构)改变围岩自稳能力。以岩体灾害控制为目标,提出了以“应力主控”为核心的释能主控技术;建立了岩体灾害控制大小原理和弱面判据(安全系数K、冲击危险性系数U);研发了采场矿压机械模拟试验系统、采动力试验系统和蠕变及动力扰动冲击加载试验系统,实现了实验室尺度还原采动力作用下岩体变形-破裂-运动过程,为研究采动力作用下岩体力学响应提供了试验装备;分别从采场岩层控制、地质软岩巷道控制、工程软岩巷道控制及冲击地压控制4个方向进行了工程案例研究,相关研究成果在工程应用中得到了验证。

软弱地层下穿盾构施工隧道对既有铁路路基变形的影响分析

基于长春地铁2号线某盾构区间下穿长双烟铁路工程研究软弱地层下盾构隧道下穿施工引起上部铁路路基沉降的影响规律,采用FLAC3D有限元软件进行模拟,研究铁路路基在不同施工工况下的沉降分布规律,并分析了土仓压力、注浆压力及深孔注浆加固作用下铁路路基的沉降影响。分析结果表明:盾构左线施工对铁路路基的扰动大于盾构右线施工;既有铁路路基的沉降量不受土仓压力的影响,但随着注浆压力的增加而降低;采用深孔注浆加固后铁路路基的最大沉降量满足《普速铁路线路修理规则》中的规定。分析结果可为软弱地层条件下盾构下穿铁路路基施工提供一定的参考依据。

Surface subsidence due to underground mining operation under weak geological condition in Indonesia

Subsidence analysis and prediction with measured data have been conducted and applied to local strata and mining conditions worldwide. Underground coal mines chose the most suitable analysis and prediction method for them. However, there was no study based on the measured data of subsidence induced by underground mining operation in Indonesia. This paper describes the condition of underground coal mine in Indonesia and then discusses the subsidence behavior due to longwall mining operation based on measured data in Balikpapan coal-bearing formation in Indonesia.

地下连续墙防绕流水囊设计与施工

在富水软弱地层地下连续墙施工过程中,墙体接头防绕流措施是增强地下连续墙整体刚度和防渗性能,提高墙体施工质量的关键。依托佛山地铁绿岛湖中站工程,在传统防绕流措施的基础上提出新型防绕流水囊技术,通过水囊对工字钢腹板内部进行填充,封堵混凝土绕流通道,提供软弱土层临时支撑。相比传统防绕流措施,采用防绕流水囊技术后,地下连续墙浇筑速率、工字钢接头施工质量和整体防水性能显著提高。

软弱地层勘察数据分析及隧洞加固方案研究

文中结合实际隧洞工程案例,通过对软弱地层勘察数据的分析研究,探索有效的隧洞加固方案。采用系统化方法对软弱地层进行研究,分析了人工填土、卵石夹角砾、碎石土和全风化黑云石英片岩的不同力学指标,并针对隧洞工程可能出现的问题,提出了相应的加固解决方案。通过对不同地质条件下的隧洞加固案例进行分析,研究发现了一些有益的经验和规律,可为隧洞工程设计和施工提供参考依据。

软弱地层盾构穿越老旧民居变形规律分析

老旧浅基础民居安全性较低,盾构穿越会对其造成不利影响。本文以杭州某出入线段盾构穿越老旧民居为背景,分析盾构穿越民居变形规律,探讨盾构穿越民居掘进参数最优区间。结果表明,出入线段无论先下穿后侧穿或先侧穿后下穿,民居竖向位移曲线较一致,且第一次穿越前后变形较小,第二次穿越时变形迅速增大,主要表现为沉降;盾构埋深、注浆参数等对老旧民居变形、倾斜影响较大;地表沉降曲线大致呈漏斗形,出线段施工对地表变形影响较小,入线段施工对出线段地表变形影响较大,对自身上部土体变形影响较小。

堤防工程中堆载预压数值模拟研究

软土地层具有含水量高、压缩性高、承载力低等特性,因此项目开展前需要对软土进行加固处理以保证足够的承载能力。堆载预压作为软土地基处理方法之一,其工艺简单、加固效果显著等优点,在堤防工程软基处理中得到了广泛的应用。本文以广州南沙某堤防工程项目为例,借助有限元软件建立计算模型,并将数值模拟计算结果与工程实测结果进行了对比,结果表明,两者数据之间变化趋势相一致,拟合度较高。本次研究结果可为今后类似工程提供借鉴。

煤层巷道顶板复合岩层组合特征与支护设计研究

煤层巷道顶板岩层组合结构复杂多变,顶板支护设计若缺乏有效指导,会导致冒顶事故发生。本文以羊场湾煤矿为工程背景,综合采用现场实测和理论分析方法,探测巷道顶板岩层结构组合特征,研究巷道顶板横向裂隙带和煤薄弱离层区域分布规律,提出支护设计方案。研究结果表明,巷道顶板岩层主要由顶煤、细粒砂岩、粉砂岩、砂质泥岩和中粒砂岩复合组成,浅部顶板0~2.5 m范围存在较多的横向裂隙破碎带和煤线发育区,中部顶板3~4 m范围岩层稳定,深部顶板5.0~6.5 m范围存在薄弱易离层五花肉“煤层+砂质泥岩+煤层”的组合结构,该结构整体厚度为1.0~1.5 m,此区域易发生离层膨胀和剪切错动,提出的支护设计方案能够满足现场安全生产要求,此设计方法能够为煤矿巷道顶板事故的防治提供科学合理的支护措施。

软弱地层基坑开挖对下卧集群隧道影响分析

基坑开挖引起土层应力重分配,尤其是软弱地层基坑开挖引起的土体卸荷会导致下卧隧道发生隆起变形。依托工程实例,通过有限元分析研究软弱地层基坑开挖对下卧集群隧道的影响,确定隧道上方软弱地层基坑开挖关键技术方案。通过对比分析,对区间隧道上方地层进行预处理后,通过严格遵循分区、分块、分层、对称、限时的开挖原则,能有效保障下卧集群隧道的安全。

软弱地层小半径大坡度盾构施工控制技术研究

软弱地层中小半径大坡度盾构掘进质量的控制一直是盾构施工控制的难点,以广州地铁七号线西延顺德段美的大道站-北滘新城站区间隧道盾构施工为例,对软弱地层小半径曲线大坡度盾构施工中存在的管片错台及盾体下沉等风险原因进行分析,提出解决措施,并结合工程实际分析了采取相应控制措施后的实施效果,为后续同类工程施工提供经验借鉴。

软弱地层大型泵站深基坑工程施工期安全监测分析

结合台州某大型泵站工程,对软弱地层大型深基坑工程施工期土体与围护结构变形特征进行研究,通过对不同施工节点围护桩表面变形、深层水平位移等4个监测数据,探究其变形规律,进行安全性分析,对比总结软土深基坑的变形特点。结果表明:围护结构变形与开挖深度大小紧密相关,且变形量在基坑开挖期间发展迅速,变化速率在开挖至设计标高后达到峰值;在底板浇筑到结构施工阶段,各监测项目变形速率呈现逐渐减小的趋势;泵站施工对周围环境影响主要在基坑开挖期间;处于软弱地层下的围护结构,其水平位移相较于一般地层变形较小而竖向沉降变形较大;对于基坑底处于淤泥质土等软弱土层的工程,地基处理能起到较好的沉降控制效果。

钢管模袋混凝土桩竖向承载性能试验研究

为揭示钢管膜袋桩在杂填土、淤泥质土、粉质黏土等软弱地层中应用的效果和其竖向承载性能影响因素和规律,本文依托同安区白云大道工程西洋溪中桥临边支护工程,通过在现场抽取4根钢管模袋混凝土桩作为试验桩,桩身埋设应变片,实测不同荷载下的沉降值,建立数值模型得到Q-S曲线、桩身轴力、桩侧摩阻力,数字模型结果与实测结果进行对比,找出提高钢管模袋混凝土桩竖向承载性能的影响规律因素和规律,给类似工程采用钢管膜袋桩支护提供参考。

富水软弱地层常压开仓综合施工技术

本文依托广州市某轨道交通工程,为避免双仓式泥水盾构在富水软弱地层盾构掘进作业中出现堵管、堵仓现象和影响掌子面稳定的不理想现象,提出针对富水软弱地层条件下盾构掘进常压开仓的新施工技术。该技术通过对加固及开仓位置地质分析与泥水平衡的压力控制,采用惰性注浆+丙烯酸盐化学注浆双重加固,实时控制注浆压力、配方、粘度以及混合比,分析地面沉降数据,通过抽芯取样等方式检测浆液的稳定性和可挖性,增强其支护性能以保证人员安全开仓换刀,加装新型搅拌棒,充分搅拌处理堆渣堆积的问题。研究表明:(1)新技术可使掌子面更为稳定,地面沉降值与速率远优于传统做法;(2)形成了新的高强度骨架网格固结体,提高土体加固、砂层堵水性能及稳定作用,保障开仓过程中的安全稳定;(3)新型搅拌棒可极大解决浮渣漂浮导致的堵管堵仓现象,研究成果可为盾构富水砂层提供有效的施工指导。

Punch Multi-slice Longwall Mining System for Thick Coal Seam under Weak Geological Conditions

Most of coal is produced from open-cut mines in Southeast Asian countries. However, the conditions of their surface mines are worsening each year： the stripping ratio is increasing, approaching economic ratio and the regulation of environmental protection. To meet the demand for coal, underground mines have to be developed in the near future. Under these circumstances, the development of new coal mines from open-cut highwalls are being planned in Southeast Asian Countries. Moreover, some of the Southeast Asian mines have thick coal seams. However, if the conventional mining systems and designs introduced in US, Australia and European Countries are applied, several geotechnical issues can be expected due to the mines＇ weak geological conditions. From these backgrounds, this paper proposed a punch multi-slice mining system with stowing for thick coal seam under weak geological conditions and discussed its applicability and suitable design by means of numerical analysis.

高压旋喷锚索在淤泥地层基坑支护中的应用

为了研究高压旋喷锚索支护在深厚软弱土层中的应用效果,本文以广州南沙某深基坑项目为例,场地淤泥厚度平均30 m~55 m,支护结构采用支护桩+高压旋喷锚索的支护形式,整个基坑开挖期间,支护结构始终处于安全的状态,各项监测数据均满足规范要求。通过对锚索轴力全过程监测发现,锚索轴力的实测值仅为设计值的55%~60%左右,说明锚索轴力并没有被充分利用,尚存在很大的潜力没有发挥出来,在深厚软弱土层中具有良好的适用性。本基坑支护形式的应用可为类似软土地区基坑工程提供经验借鉴。