Detection and treatment of water inflow in karst tunnel：A case study in Daba tunnel

In a karst tunnel, fissures or cracks that are filled with weathered materials are a type of potential water outlet as they are easily triggered and converted into groundwater outlets under the influence of high groundwater pressure. A terrible water inrush caused by potential water outlets can seriously hinder the project construction. Potential water outlets and water sources that surrounding the tunnel must be detected before water inflow can be treated. This paper provides a successful case of the detection and treatment of water inflow in a karst tunnel and proposes a potential water outlet detection(PWOD) method in which heavy rainfall(>50 mm/d) is considered a trigger for a potential water outlet. The Daba tunnel located in Hunan province, China, has been constructed in a karst stratum where the rock mass has been weathered intensely by the influence of two faults. Heavy rain triggered some potential water outlets, causing a serious water inrush. The PWOD method was applied in this project for the treatment of water inflow, and six potential water outlets in total were identified through three heavy rains. Meanwhile, a geophysical prospecting technique was also used to detect water sources. The connections between water outlets and water sources were identified with a 3-D graphic that included all of them. According to the distribution of water outlets and water sources, the detection area was divided into three sections and separately treated by curtain grouting.

Seepage field distribution and water inflow laws of tunnels in water-rich regions

Currently,the water inrush hazards during tunnel construction,the water leakage during tunnel operation,and the accompanying disturbances to the ecological environment have become the main problems that affect the structural safety of tunnels in water-rich regions.In this paper,a tunnel seepage model testing system was used to conduct experiments of the grouting circle and primary support with different permeability coefficients.The influences of the supporting structures on the water inflow laws and the distribution of the water pressure in the tunnel were analyzed.With the decrease in the permeability coefficient of the grouting circle or the primary support,the inflow rate of water into the tunnel showed a non-linear decreasing trend.In comparison,the water inflow reduction effect of grouting circle was much better than that of primary support.With the increase of the permeability coefficient of the grouting ring,the water pressure behind the primary lining increases gradually,while the water pressure behind the grouting ring decreases.Thus,the grouting of surrounding rock during the construction of water-rich tunnel can effectively weaken the hydraulic connection,reduce the influence range of seepage,and significantly reduce the decline of groundwater.Meanwhile,the seepage tests at different hydrostatic heads and hydrodynamic heads during tunnel operation period were also conducted.As the hydrostatic head decreased,the water pressure at each characteristic point decreased approximately linearly,and the water inflow rate also had a gradual downward trend.Under the action of hydrodynamic head,the water pressure had an obvious lagging effect,which was not conducive to the stability of the supporting structures,and it could be mitigated by actively regulating the drainage rate.Compared with the hydrostatic head,the hydrodynamic head could change the real-time rate of water inflow to the tunnel and broke the dynamic balance between the water pressure and water inflow rate,thereby affecting the stress state on the supporting structures.

Water inflow forecasting for tunnel considering nonlinear variation of permeability coefficient

To assess the water inflow which is more suitable to the actual conditions of tunnel,an empirical correlation about the permeability coefficient changing with depth is introduced.Supposing that the surrounding rock is heterogeneous isotropy,the formula for calculating water inflow of tunnel with the nonlinear variation of permeability coefficient is deduced.By the contrast analysis with the existing formulas,the presented method has the similar value to them;moreover,the presented method has more simple form and easy to use.Due to parameter analysis,the water inflow decreases after considering the nonlinear variation of permeability coefficient.When the attenuation coefficient a>0,the water inflow increases first till reaches the maximum at a certain depth,then decreases and is close to 0 finally if deep enough.Thus,it is better to keep away from the certain depth where it is with the maximum water inflow for safe operation and economical construction,and reduce the water damage.Based on the analysis,the radius of tunnel has less impact on the amount of water inflow,and the water inflow just increases by 6.7% when the radius of tunnel increases by 1 m.

Predictive analysis of stress regime and possible squeezing deformation for super-long water conveyance tunnels in Pakistan

The prediction of the stress field of deep-buried tunnels is a fundamental problem for scientists and engineers. In this study, the authors put forward a systematic solution for this problem. Databases from the World Stress Map and the Crustal Stress of China, and previous research findings can offer prediction of stress orientations in an engineering area. At the same time, the Andersonian theory can be used to analyze the possible stress orientation of a region. With limited in-situ stress measurements, the Hock-Brown Criterion can be used to estimate the strength of rock mass in an area of interest by utilizing the geotechnical investigation data, and the modified Sheorey＇s model can subsequently be employed to predict the areas＇ stress profile, without stress data, by taking the existing in-situ stress measurements as input parameters. In this paper, a case study was used to demonstrate the application of this systematic solution. The planned Kohala hydropower plant is located on the western edge of Qinghai-Tibet Plateau. Three hydro-fracturing stress measurement campaigns indicated that the stress state of the area is SH - Sh 〉 Sv or SH 〉Sv 〉 Sh. The measured orientation of Sn is NEE （N70.3°-89°E）, and the regional orientation of SH from WSM is NE, which implies that the stress orientation of shallow crust may be affected by landforms. The modified Sheorey model was utilized to predict the stress profile along the water sewage tunnel for the plant. Prediction results show that the maximum and minimum horizontal principal stres- ses of the points with the greatest burial depth were up to 56.70 and 40.14 MPa, respectively, and the stresses of areas with a burial depth of greater than 500 m were higher. Based on the predicted stress data, large deformations of the rock mass surrounding water conveyance tunnels were analyzed. Results showed that the large deformations will occur when the burial depth exceeds 300 m. When the burial depth is beyond 800 m, serious squeezing deformations will occur in the surrounding rock masses, thus requiring more attention in the design and construction. Based on the application efficiency in this case study, this prediction method proposed in this paper functions accurately.

Energy analysis of face stability of deep rock tunnels using nonlinear Hoek-Brown failure criterion

The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the analytical solutions of collapse pressure were derived through utilizing the virtual power principle in the case of pore water, and the optimal solutions of collapse pressure were obtained by using the optimization programs of mathematical model with regard of a maximum problem. In comparison with existing research with the same parameters, the consistency of change rule shows the validity of the proposed method. Moreover, parametric study indicates that nonlinear Hoek-Brown failure criterion and pore water pressure have great influence on collapse pressure and failure shape of tunnel faces in deep rock masses, particularly when the surrounding rock is too weak or under the condition of great disturbance and abundant ground water, and in this case, supporting measures should be intensified so as to prevent the occurrence of collapse.

3D Finite Element Simulation of Tunnel Boring Machine Construction Processes in Deep Water Conveyance Tunnel

Applying stiffness migration method,a 3D finite element mechanical model is established to simulate the excavation and advance processes.By using 3D nonlinear finite element method,the tunnel boring machine(TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment.The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution.The stress increases slightly and limitedly in the course of excavation.The maximum and minimum displacements of segment,manifesting as zonal distribution,distribute in arch bottom and vault respectively.The displacements slightly increase with the advance of TBM and gradually tend to stability.

New empirical model to evaluate groundwater flow into circular tunnel using multiple regression analysis

There are various analytical, empirical and numerical methods to calculate groundwater inflow into tun- nels excavated in rocky media. Analytical methods have been widely applied in prediction of groundwa- ter inflow to tunnels due to their simplicity and practical base theory. Investigations show that the real amount of water infiltrating into jointed tunnels is much less than calculated amount using analytical methods and obtained results are very dependent on tunnel＇s geometry and environmental situations. In this study, using multiple regression analysis, a new empirical model for estimation of groundwater seepage into circular tunnels was introduced. Our data was acquired from field surveys and laboratory analysis of core samples. New regression variables were defined after perusing single and two variables relationship between groundwater seepage and other variables. Finally, an appropriate model for estima- tion of leakage was obtained using the stepwise algorithm. Statistics like R, R2, R2e and the histogram of residual values in the model represent a good reputation and fitness for this model to estimate the groundwater seepage into tunnels. The new experimental model was used for the test data and results were satisfactory. Therefore, multiple regression analysis is an effective and efficient way to estimate the groundwater seeoage into tunnels.

Grouting techniques for the unfavorable geological conditions of Xiang'an subsea tunnel in China

One of the major challenges during subsea tunnel construction is to seal the potential water inflow. Thepaper presents a case study of Xiang＇an subsea tunnel in Xiamen, the first subsea tunnel in China. Duringits construction, different grades of weathered geomaterials were encountered, which was the challengingissue for this project. To deal with these unfavorable geological conditions, grouting was adoptedas an important measure for ground treatment. The grouting mechanism is first illustrated by introducinga typical grouting process. Then the site-specific grouting techniques employed in the Xiang＇ansubsea tunnel are elaborated. By using this ground reinforcement technique, the tunneling safety of theXiang＇an subsea tunnel was guaranteed. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Approximate analytical solution for seepage field of drained tunnel in vertically stratified phreatic aquifer

To explore the water table and water inflow after tunnel excavation in a vertically stratified phreatic aquifer,approximate analytical solutions for the steady-state water table and water inflow of a drained tunnel in a vertically stratified phreatic aquifer were obtained based on the Dupuit assumptions and the integral method.By comparing the approximate analytical solutions with numerical solutions,it was found that the relative error of the approximate analytical solution for the water table elevation is less than 10%,and the relative error of the approximate analytical solution for the water inflow is approximately 25%.The sources of the above errors are as follows:(1)At the lateral boundary of water replenishment,the water surface should be tangent to the horizontal line,but the water surface for the approximate analytical solutions has a gradient.(2)At the vertical boundaries near the tunnel,the total head is variable,but the total head for the approximate analytical solutions is assumed to be constant.(3)The Dupuit assumptions are applied in the flow domain near the tunnel.Although the relative errors of the approximate analytical solutions for the water table elevation and water inflow are evident,the lowered water table is reflected in the approximate analytical solutions.

Grey forewarning and prediction for mine water inflowing catastrophe periods

Based on the theory of grey system, established GM （1, 1） grey catastrophe predict model for the first time in order to forecast the catastrophe periods of mine water inflowing （not the volume of water inflowing）. After establishing the grey predict system of the catastrophe regularity of 10 month-average volume of water inflowing, the grey forewarning for mine water inflowing catastrophe periods was established which was used to analyze water disaster in 400 meter level of Wennan Colliery. Based on residual analysis, it shows that the result of grey predict system is almost close to the actual value. And the scene actual result also shows the reliability of prediction. Both the theoretical analysis and the scene actual result indicate feasibility and reliability of the method of grey catastrophe predict system.

Safe retaining pressures for pressurized tunnel face using nonlinear failure criterion and reliability theory

Based on the active failure mechanism and passive failure mechanism for a pressurized tunnel face, the analytical solutions of the minimum collapse pressure and maximum blowout pressure that could maintain the stability of pressurized tunnel faces were deduced using limit analysis in conjunction with nonlinear failure criterion under the condition of pore water pressure. Due to the objective existence of the parameter randomness of soil, the statistical properties of random variables were determined by the maximum entropy principle, and the Monte Carlo method was employed to calculate the failure probability of a pressurized tunnel. The results show that the randomness of soil parameters exerts great influence on the stability of a pressurized tunnel, which indicates that the research should be done on the topic of determination of statistical distribution for geotechnical parameters and the level of variability. For the failure probability of a pressurized tunnel under multiple failure modes, the corresponding safe retaining pressures and optimal range of safe retaining pressures are calculated by introducing allowable failure probability and minimum allowable failure probability. The results can provide practical use in the pressurized tunnel engineering.

富水岩溶地区隧道涌水预测与施工处置技术研究

针对贵州某隧道施工过程中遭遇一处连通地下暗河的大型溶洞引起隧道内大规模涌水的灾害进行研究,结合水文地质情况对涌水量进行预测和分析后,现场先对岩溶水进行初步释压,后采用水泥砂浆分步回填隧道上伏溶腔以封堵岩溶出水口;进一步采用集水管引排岩溶水的方式对剩余地下水进行二次加强处理,同时将集水管与隧道外侧的泄水洞相连,二者构成一套完整的引排水系统的处治手段。采用堵排相结合的原则有效地达到涌水处置目的,确保了隧道的安全施工,可为类似地层的隧道施工提供有益的借鉴。

水位变化下浅埋盾构隧道开挖面渗透力与稳定性研究

为分析临江地区透水地层浅埋盾构开挖面渗流作用下的稳定性,结合安庆市沿江东路管廊盾构段典型断面,建立浅埋盾构三维流固耦合数值模型,分析水位变化、土体力学性质对开挖面稳定性影响以及渗透力的变化规律,明确浅埋盾构渗透作用下开挖面的失稳形式,建立区别于传统破坏模型的圆台-弧转体数学模型,提出一种基于极限分析上限法且考虑渗透力作用的极限支护压力的计算方法,并与已有研究结果相对比,验证该方法的可行性;根据该方法分析水位、土体力学参数、盾构掘进参数对极限支护压力的影响。研究结果表明:黏聚力及内摩擦角增加会导致破坏区高度显著减小,而水位增加会导致破坏区高度及长度显著增加;开挖面上渗透力随开挖面与拱顶的距离增大而增大,渗透力随水位变化呈线性变化,平均渗透力随水位变化率为2.75 kN·m^(-3);极限支护压力随黏聚力、水位呈线性变化,随摩擦角呈非线性变化;结合开挖面前方土层土体力学性质,极限支护压力随水位变化率为5.11~5.75 kPa,与实测土仓压力变化率6.38 kPa较吻合,控制土仓压力在80 kPa以上时能有效保证开挖面稳定。

内水渗漏软化基底对盾构隧洞衬砌管片受力性能的影响分析

水工盾构隧洞在运行过程中存在内水渗漏导致基底软化的风险,基底软化将对隧洞管片受力变形产生影响。依托实际水工盾构隧洞工程,构建了由管片、灌浆体和围岩组成的三维有限元数值模型,针对Ⅴ类围岩条件下因渗漏导致基底均匀和不均匀软化的状况,研究了管片的受力性能变化规律。结果表明:在内外荷载作用下,管片的环向应力、竖向位移和定位销应力均随基底软化深度的增加而增大,均匀软化条件下仰拱管片出现峰值为1.88 MPa的拉应力,存在管片开裂风险;基底软化导致定位销应力增大,而管片竖向位移的变化幅度较小。研究成果可为水工盾构隧洞的安全运行监测提供科学依据。

水滴形大跨钢屋盖结构风洞试验和风振分析

自然风经过大跨结构时,由于结构屋顶形状不规则,通常会引起柔性屋面的振动,因此针对大跨屋面结构抗风设计需要考虑风压分布和风振响应。以陕西省水务集团矿泉水生产车间为工程背景,制作了1∶200的刚性模型,通过刚性模型风洞试验测得该水滴型大跨钢屋盖结构的表面风压,研究了屋盖表面典型测点及整体的风压分布规律。基于风洞试验数据,对结构进行风振时程分析,得到了屋盖表面的风振响应和风振系数。结合刚性模型风洞试验和风振分析,深入研究了水滴形大跨屋盖结构的风压分布规律和风致振动特性,并总结了其共性规律。

内蒙古母杜柴登煤矿3^(-1)煤充水条件及矿井涌水量预测

母杜柴登煤矿矿井涌水量大,且属于高矿化度水,面临着大量疏排矿井涌水和矿井水地面处理的压力。在分析矿区地质及水文地质条件的基础上,认为开采3^(-1)煤层时,矿井水来源于3^(-1)煤顶板─直罗组底界砂岩含水层,包括直罗组底部中、粗粒砂岩含水层和3^(-1)煤顶板延安组三段砂岩含水层。运用大井法和达西定律计算的30209工作面涌水量分别为931m^(3)/h、919m^(3)/h,与实际接近。研究可为工作面侧向注浆封堵(含水层改造)、帷幕截流减量的可行性和减量程度提供依据。

隧道富水断层破碎带突涌预报与工程对策研究

为解决高原隧道断层破碎带易发突泥冒顶灾害的问题,采用现场调查、地面物探、洞内地震波反射法、瞬变电磁法、超前钻孔等超前地质预报方法,推广洞内物探三维分析,对富水断层破碎带突泥灾害特征、超前地质预报综合成果和工程应对加固措施进行研究。结果表明:三维物探成果能快速精准查明富水破碎带空间形态,成果直观,有效指导风险判识和工程处置措施;对富水断层带预报应充分结合勘察期成果,宏观初判断层分布特性,洞内采用物钻结合、长短结合的方法;首次提出按照“探明破碎带规模形态,查明破碎带物质组分性状,观测地下水特征变化情况”的思路,研判突泥涌水风险;施工处置应按照“探泄结合,先固后进,回堵再泄”的总体原则有序开展。研究成果和手段可为类似突涌灾害超前地质预报和工程应对措施提供参考。

富水砂卵石层盾构施工影响因素及敏感性分析

砂卵石地层具有渗透性强、孔隙率大、自稳性差和受扰反应大等特点,若盾构施工参数控制不当则会发生掌子面失稳、坍塌和涌水等安全事故。确定富水砂卵石层盾构掘进引起地表沉降和管片隧道变形的影响因素,对于安全施工具有重要的指导意义。本文以洛阳地铁区间盾构穿越洛河富水砂卵石地层为工程背景,基于流固耦合理论,运用ABAQUS软件构建盾构掘进的三维有限元模型,数值模拟和现场实测的地表沉降数据基本吻合,验证了模型的准确性。采用单因素分析法研究了盾构掘进压力、同步注浆压力和等代层厚度等3个参数对地表沉降与管片变形的影响规律,研究结果表明:增大盾构掘进压力和同步注浆压力,减小等代层厚度,均能减小地表和隧道的拱顶沉降;而增大盾构掘进压力,减小同步注浆压力和等代层厚度,可减小隧道拱腰的水平变形。采用正交试验方法确定了3个影响因素对地表沉降和管片拱顶沉降两个指标的敏感性,从大到小排序均为:同步注浆压力、盾构掘进压力和等代层厚度。

基于TBM掘进大数据和特征参数的引水隧洞塌方分析

针对TBM掘进过程中缺乏对围岩质量和塌方风险快捷、精准的预测预警方法,通过对TBM掘进大数据的深入挖掘,结合对实际工程塌方数据的剖析,提出潜在塌方风险的辅助判断依据。首先,对冗杂、连续的原始采集数据进行预处理,获取高质量的分析数据;然后,基于参数的相关性分析提出围岩特征参数的计算方法,并围绕特征参数的合理性和适用性,通过理论推导、室内试验和现场原位掘进试验进行论证;最后,结合实际的TBM塌方案例分析特征参数与围岩地质情况的相关性,提出塌方风险快速判断依据。结果表明:基于TBM掘进数据获取的围岩特征参数在一定程度上反映了围岩质量,其数值与围岩质量正相关,当其数值显著降低、变幅超过69.2%时,当前的掘进循环极大可能存在塌方风险。

隧道涌水量预测计算方法综述

预测隧道涌水量对于保障隧道施工安全、进度、洞室稳定和人身安全问题至关重要。国内外学者已提出多种预测方法,但是存在不同适用条件,根据隧道的水文地质条件选取恰当的方法能有效提高预测精度。对解析公式法、经验公式法、数值法、随机性数学模型预测法等多种涌水量预测方法进行了系统梳理和分析,通过对这些方法的基本原理及适用条件进行综合分析,讨论了当前涌水量预测方法存在的不足之处,并提出改进方向。结果表明:解析公式法应用简单,但结果偏差较大;经验公式法源于工程案例总结,适用于相似条件下隧道涌水量预测;数值法通过数学模型模拟,可以解决复杂水文地质条件下的涌水量预测,但对勘察设计阶段获取的水文地质参数提出更高的要求;随机性数学模型方法需要大量数据来保证结果的准确性;其他方法主要依赖于地理信息系统(GIS)技术、同位素分析法等手段,通过科学分析来识别并判断地下水量及其流动通道的地质特征,需要充分的数据支持和详尽的地下勘探结果作为依据。研究成果可为实际工程中选择合适的涌水量预测方法提供参考。