Support design method for deep soft-rock tunnels in non-hydrostatic high in-situ stress field

Due to the long-term plate tectonic movements in southwestern China,the in-situ stress field in deep formations is complex.When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field,tunnels will suffer serious asymmetric deformation.There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness.This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve(GSC)and ground loosening curve(GLC).Then,based on the convergence confinement theory,the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures.In addition,this method can provide the clear support time and support stiffness of the second layer of initial support.The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China.Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field.Field applications showed that the secondary lining could be constructed properly.

Experimental study on the effect of flexible joints of a deep-buried tunnel across an active fault under high in-situ stress conditions

During dislocation,a tunnel crossing the active fault will be damaged to varying degrees due to its permanent stratum displacement.Most previous studies did not consider the influence of the tunnel’s deep burial and the high in-situ stress,so the results were not entirely practical.In this paper,the necessity of solving the anti-dislocation problem of deep-buried tunnels is systemically discussed.Through the model test of tunnels across active faults,the differences in failures between deep-buried tunnels and shallow-buried tunnels were compared,and the dislocation test of deep-buried segmental tunnels was carried out to analyze the external stress change,lining strain,and failure mode of tunnels.The results are as follows.(1)The overall deformation of deep-buried and shallow-buried tunnels is both Sshaped.The failure mode of deep-buried tunnels is primarily characterized by shear and tensile failure,resulting in significant compressive deformation and a larger damaged area.In contrast,shallow-buried tunnels mainly experience shear failure,with the tunnel being sheared apart at the fault crossing,leading to more severe damage.(2)After the segmental structure design of the deep-buried tunnel,the‘‘S”deformation pattern is transformed into a‘‘ladder”pattern,and the strain of the tunnel and the peak stress of the external rock mass are reduced;therefore,damages are significantly mitigated.(3)Through the analysis of the distribution of cracks in the tunnel lining,it is found that the tunnel without a segmental structure design has suffered from penetrating failure and that cracks affect the entire lining.The cracks in a flexible segmental tunnel affect about 66.6%of the entire length of the tunnel,and cracks in a tunnel with a short segmental tunnel only affect about 33.3%of the entire length of the tunnel.Therefore,a deep-buried tunnel with a short segmental tunnel can yield a better anti-dislocation effect.(4)By comparing the shallow-buried segmental tunnel in previous studies,it is concluded that the shallow-buried segmental tunnel will also suffer from deformation outside the fault zone,while the damages to the deep-buried segmental tunnel are concentrated in the fault zone,so the anti-dislocation protection measures of the deep-buried tunnel shall be provided mainly in the fault zone.The results of the above study can provide theoretical reference and technical support for the design and reinforcement measures of the tunnel crossing active fault under high in-situ stress conditions.

Practices on rockburst prevention and control in headrace tunnels of Jinping II hydropower station

Rockburst problems induced by high in-situ stresses were prominent during construction of the headrace tunnels of Jinping II hydropower station. The rockbursts occurred in various forms, and it is necessary to take pertinent measures for integrated prevention and control of rockbursts. In view of the rockburst characteristics during tunnel construction of Jinping II hydropower station, the engineering geological conditions were presented, and the features, mechanisms and forms of rockbursts observed during construction were analyzed in detail. A large number of scientific researches, experiments and applications were conducted. Multiple measures were adopted to prevent and control rockbursts, including the prediction and early warning measures, stress relief by blasting in advance, optimized blasting design and optimized tunnel support in the tunnel sections prone to strong rockbursts. The effectiveness of these prevention and control measures was evaluated. Experiences have been accumulated through a great number of helpful explorations and practices for rockburst prevention and control. A comprehensive rockburst prevention and control system has been gradually established.

A review of rockburst:Insights from engineering sites to theoretical investigations

Rockburst has perennially posed a formidable challenge to the stability of underground engineering works,particularly under conditions of deep-seated high stress.This paper provides a comprehensive review of recent advancements in on-site research related to rockburst occurrences,covering on-site case analyses,monitoring methodologies,early warning systems,and risk(proneness)evaluation.Initially,the concepts and classifications of rockburst based on on-site understanding were summarized.The influences of structural planes(in various spatial distribution combinations),in-situ stress(particularly magnitude and direction of the principal stress),dynamic disturbances,and excavation profiles on rockburst were thoroughly assessed and discussed through the analysis of published rockburst cases and on-site survey results.Subsequently,a compendium of commonly employed on-site monitoring techniques was outlined,delineating their respective technical attributes.Particular emphasis is accorded to the efficacy of microseismic monitoring technology and its prospective utility in facilitating dynamic rockburst early warning mechanisms.Building upon this foundation,the feasibility of assessing rockburst propensity while considering on-site variables is verified,encompassing the selection and quantitative evaluation of pertinent indicators.Ultimately,a comprehensive synthesis of the paper is presented,alongside the articulation of prospective research goals for the future.

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.

Influence of maximum principal stress direction on the failure process and characteristics of D-shaped tunnels

To investigate the failure process and characteristics of D-shaped tunnels under different maximum principal stress directions θ, true-triaxial tests were conducted on cubic sandstone samples with a through D-shaped hole. The test results show that the failure process can be divided into 4 periods:calm, buckling deformation, gradual buckling and exfoliation of rock fragment, and formation of a Vshaped notch. With an increase in θ from 0° to 90°, the size of the rock fragments first decreases and then increases, whereas the fractal dimension of the rock fragments first increases and then decreases. Meanwhile, the failure position at the left side shifts from the sidewall to the corner and finally to the floor, whereas the failure position at the right side moves from the sidewall to the spandrel and finally to the roof, which is consistent with the failure position in underground engineering. In addition, the initial vertical failure stress first decreases and then increases. By comparing the results,the failure severities at different maximum principal stress directions can be ranked from high to low in the following order: 90°>60°>30°>45°>0°.

Influence of deviatoric stress on rockburst occurrence:An experimental study

As mining delves deeper into the crust, it is necessary to investigate the complex rock responses associated with higher stress gradients. Therefore, it is essential to better understand the mechanisms associated with the rockburst phenomenon. However, due to the large-scale and difficult monitoring of real mining excavations, laboratory scale tests must be utilised to determine the conditions conducive to burst. To this end, this research focuses on the implementation of a new rockburst testing apparatus to replicate the stress conditions of a rock mass excavation at the time of bursting. This apparatus allows the determination of rockburst stresses and a relationship between deviatoric stress and in-situ pressure/depth. Using this relationship it is then possible to estimate the standardised stress levels for a certain rock type which might lead to rockburst occurrence. Furthermore, it is demonstrated that with increasing in-situ pressure, the likelihood(measured as a lower differential stress) and the extent(indicated by the increasing range of deviatoric stress) of rockburst increases. These findings provide valuable information about the conditions necessary for bursting in deep mining.

THE EFFECTS OF THREE-DIMENSIONAL PENNY-SHAPED CRACKS ON ZONAL DISINTEGRATION OF THE SURROUNDING ROCK MASSES AROUND A DEEP CIRCULAR TUNNEL

In this study, it was assumed that three-dimensional penny-shaped cracks existed in deep rock masses. A new non-Euclidean model was established, in which the effects of penny- shaped cracks and axial in-situ stress on zonal disintegration of deep rock masses were taken into account. Based on the non-Euclidean model, the stress intensity factors at tips of the penny- shaped cracks were determined. The strain energy density factor was applied to investigate the occurrence of fractured zones. It was observed from the numerical results that the magnitude and location of fractured zones were sensitive to micro- and macro-mechanical parameters, as well as the value of in-situ stress. The numerical results were in good agreement with the experimental data.

基于隧道施工阶段地应力实测数据的岩爆判据研究

云南省蔓金高速草果山隧道属于深埋长隧道,隧道围岩坚硬完整且脆性较高,隧道施工阶段面临着岩爆发生的风险。因此,采用应力解除法进行地应力测量,并基于实测数据结合现场岩爆发生情况与国内外不同的强度判据进行对比,并对岩爆判据的适用性进行分析研究。最后,根据岩爆实际发生的情况和位置对岩爆判据进行验证分析,结果表明:岩爆预测标准除应力指标外,还应使用多因素指标进行综合判别;某种岩爆预测方法不能适用所有地下工程,应结合工程的具体情况,进行岩爆危险性评估,为工程提出岩爆防治措施。同时此研究成果为深埋完整硬岩的岩爆灾害分析预测和防控提供了参考依据。

深部极高地应力花岗岩隧道岩爆破坏特征及成因机理研究

深部极高地应力花岗岩隧道施工过程中,岩爆灾害异常突出,硬岩岩爆不同程度地造成岩体片状剥落、棱板状破裂、岩块抛掷及强烈弹射等。为了揭示花岗岩隧道岩爆成因机制,综合地质调绘、监控量测、岩爆实录统计、室内岩石力学试验、微观分析和数值模拟分析等方法对隧道高地应力及岩爆的形成、破坏特征及影响因素进行探讨分析。根据现场岩爆实录统计分析,花岗岩隧道岩爆破坏特征复杂多样,发生时间集中,高水平构造应力使靠近雅鲁藏布江河谷一侧岩爆烈度显著增大,大埋深高自重应力导致岩爆主要分布在隧道掌子面和拱顶。基于钻孔实测地应力数据和初始地应力场反演分析,发现花岗岩隧道地应力场由构造应力和自重应力共同主导,隧道沿线82.0%的区段处于高到极高地应力状态,为岩爆的发生提供内动力地质条件。室内岩石力学试验表明二长花岗岩和花岗闪长岩均具有中等岩爆倾向性,厚层状、强度大、刚度高、完整性好的岩体为岩爆提供充足的物源条件。受控于雅鲁藏布江缝合带地质构造作用以及新生代岩浆活动作用影响,花岗岩隧道呈现高地温特征,地温梯度为5.5℃/100 m,最高实测地温达到89.6℃,高温热力耦合作用加速岩爆发生并提高岩爆危险性等级。隧道施工工艺会改变围岩应力重分布,影响围岩的应力集中,造成一定的尺寸效应,影响岩爆发生的烈度等级、时间和空间分布。

岩爆隧道冲击荷载作用特征及其计算方法

隧道中的硬脆围岩在高地应力情况下易发生岩爆,而目前国内针对岩爆隧道的支护结构设计主要采用工程类比法.为了量化作用在支护结构上的岩爆冲击荷载,从能量角度分析岩爆过程中的能量转化关系,利用动能定理及能量守恒原理计算冲击荷载,并结合隧道松散压力提出隧道发生岩爆时的荷载计算方法,同时探明洞径等不同因素对岩爆作用范围的影响规律;结合某高地应力隧道岩爆段对其合理性进行验证.研究结果表明:岩爆冲击荷载计算公式中,动荷因数与隧道支护所采用结构刚度正相关;在相同跨度与地应力条件下,圆形隧道的岩爆深度小于马蹄形隧道,岩爆横向范围大于马蹄形隧道;在相同洞形和地应力条件下,随着隧道跨度越大,岩爆深度与横向范围越大;在相同洞形和跨度条件下,地应力值越高,岩爆深度与横向范围越大;单线隧道Ⅱ级围岩岩爆荷载为12.02~337.75 kPa,单线隧道Ⅲ级围岩岩爆荷载为25.36~352.12 kPa,双线隧道Ⅱ级围岩岩爆荷载为8.54~288.55 kPa,双线隧道Ⅲ级围岩岩爆荷载为33.11~300.83 kPa.

特长深埋隧道岩爆倾向性预测与影响因素研究

岩爆倾向性预测是深埋硬岩隧道工程施工的难点,以往研究多以隧道施工中现场监测数据为预测基础,但预测结果存在时效性和局限性。从西南地区某特长深埋隧道工程区地应力现场实测数据出发,对区域地应力场进行三维数值反演分析,获取隧道轴向地应力特征,从而对隧道施工中岩爆倾向性等级进行预测,并利用数值模拟手段对岩爆影响因素进行对比分析,其结果可为类似特长深埋隧道工程提供参考。研究结果表明:①实测点附近三向主应力总体趋势为:σ_(H)>σ_(v)>σ_(h),其中最大水平主应力σ_(H)值为10.96~17.07 MPa,方向N9°W~N7°E;②隧道轴向最大水平主应力σ_(H)最大值为23.88 MPa,最小水平主应力σ_(h)较恒定;竖向主应力σ_(v)最大值为46.70 MPa,其量值变化和隧道埋深呈正相关。该隧道具备岩爆发生的基本条件,施工中存在中等、强烈岩爆风险;③侧压系数为0.8时,墙角处岩爆倾向性较大,其他各部位倾向性相同;埋深越大,岩爆倾向性越大,且各部位岩爆倾向性受埋深的影响程度基本一致;围岩弹性模量为40 GPa时,岩爆倾向性最大;围岩内摩擦角大于40°时,隧道断面各部位岩爆倾向性趋于平稳。

A critical review on the developments of rock support systems in high stress ground conditions

Extreme ground behaviour in high-stress rock masses such as rockburst prone and squeezing ground conditions are encountered in a range of underground projects both in civil and mining applications.The occurrence of such ground behaviour types are difficult to predict and special design and construction measures must be taken to control them.Determining the most appropriate support system in such grounds is one of the major challenges for ground control engineers because there are many contributing factors to be considered,such as the rock mass parameters,the stress condition,the type and performance of the support systems,the condition of major geological structures and the size and geometry of the underground excavation.The main characteristics and support requirements of rockburst-prone and squeezing ground conditions are herein critically reviewed and characteristics of support functions are discussed.Different types of energy-absorbing rockbolts and other support elements applicable for ground support in burst-prone and squeezing grounds are introduced.Important differences in the choice and economics of ground support strategies in high-stress ground conditions between civil tunnels and mining excavations are discussed.Ground support benchmarking data and mitigation measures for mines and civil tunnels in burst-prone,squeezing and heavily swelling grounds conditions are briefly presented by some examples in practice.

深埋高地应力TBM隧道岩爆发生机理研究

为分析高地应力隧道岩爆发生机理,以西南山区某新建TBM隧道为工程背景,通过室内岩石力学试验分析围岩基本力学特性,然后基于弹性力学理论建立板裂屈曲岩爆的力学失稳模型,最后通过离散元UDEC软件对隧道岩爆演化过程进行分析。结果表明:①隧道围岩满足发生岩爆的岩性条件,岩爆倾向性为中等~强烈;②拱顶板裂屈曲岩爆可视为围岩板裂结构在水平切向应力作用下断裂失稳所导致,劈裂岩体厚度为岩爆主要影响因素;③隧道开挖卸荷后洞壁围岩开裂剥离弹射破坏主要是张拉破坏造成。为保障隧道施工安全提供理论依据。

高地应力隧道滞后型岩爆时空特征影响因素

木匪岭隧道滞后型岩爆频发,对于其时空破坏特征影响因素研究不足。本文基于现场岩爆统计资料和地应力测试,阐释了滞后型岩爆时空分布特征和主要诱因。通过有限差分软件计算并总结了不同影响因素下滞后型岩爆作用规律。结果表明:滞后型岩爆约占所有统计岩爆的13%,以中等烈度为主,且具有明显的时空破坏特征。水平向高地应力作用下洞周局部应变能密度较大,加之围岩局部节理裂隙较发育,容易诱发岩爆。随着水平向构造应力逐渐提高,滞后型岩爆发生的可能性显著增加,且呈现向突变型岩爆转变的趋势。应力释放系数较小或较大都会导致岩爆的发生,建议围岩应力释放系数在30%~60%时进行初期支护,以有效抑制滞后型岩爆的发生。研究结果可为预测和抑制滞后型岩爆发生提供依据。

巨龙铜矿地应力对大断面巷道稳定性与岩爆倾向性数值模拟

分析矿山深部巷道稳定性及岩爆倾向性对于矿山安全建设具有重要意义。以巨龙铜矿大断面深埋长巷道为研究对象,利用数值模拟手段探究了青藏高原地应力影响下环形排水巷稳定性,分析了巷道掘进后岩爆倾向性。结果表明,环形排水巷道围岩内应力以水平应力为主,最大主应力为32 MPa,在16段排水巷道中,应力主要集中于巷道DE、EF、DG段。巷道围岩水平位移大于垂直位移,环形排水巷道最大位移以M点为中心向四周扩散。GM段、HL段、KN段巷道围岩均发生了较大变形,对于该区域巷道应加强支护。巷道DE、EF、DG段最大弹性应变达到1.01×10^(5) J/m^(3),呈现出岩爆倾向,可通过减小开挖进尺削弱岩体局部应力集中。现场监测表明模拟结果可靠。该研究结果为巨龙铜矿环形排水巷施工及地压灾害防控提供了理论参考。

高地应力水平岩层隧道滞后型岩爆时空倾向性机制分析

浙江杭温水平岩层隧道内滞后型岩爆频发,但目前对于其孕育机理和时空倾向性研究不足。故采用有限差分软件,通过地应力测试和统计现场岩爆资料的方法,研究分析滞后型岩爆时空特征机制。结果表明:①滞后型岩爆具有明显的时空倾向性特征。近70%的滞后型岩爆时间上发生在该区开挖6~30 d,空间上滞后于掌子面30~100 m之间;且多发生中等岩爆,岩爆等级及可能性随时空变化呈现倒“V”形趋势。②硬岩在高地应力环境中具有明显的延性与时效变形特征;在卸荷条件下,应力释放率的逐渐增加是诱发滞后型岩爆的最主要因素。③开挖一定距离后,隧道周边不同位置处都出现应变能突变,且保持较高的应变能密度,易发生等级较高的岩爆。上述结果为以后预测滞后型岩爆和施加相应支护措施提供了依据。

高地应力水平层状硬岩隧道岩爆分级与防控技术研究

本文依托乐汉高速大峡谷隧道,总结分析了高地应力水平层岩爆的特征并提出了岩爆分级标准。在岩爆分级的基础上,提出了针对不同岩爆等级的处置措施。现场实践结果表明,对于弱岩爆可以采用全断面法开挖,降低扰动次数。对于中~强岩爆段,宜采取短进尺分部开挖,降低爆破对围岩的一次性扰动,同时采取应力释放孔、应力解除爆破孔等辅助措施提前释放围岩应力。

西南山区某隧道地应力特征及岩爆危险性评价

研究目的:西南山区花岗岩隧道地处雅鲁藏布江缝合带地区,地质条件极其复杂,区域地质构造作用强烈,隧道建设中面临的高地应力及岩爆灾害风险异常显著。根据隧址区地质资料,结合附近工程区的地应力测试数据,通过COMSOL建立隧道数值计算模型,采用边界荷载调整法反演分析隧址区的初始地应力场,研究分析隧址区的地应力特征,并探讨花岗岩隧道沿线岩爆危险性等级。研究结论:(1)花岗岩隧道轴线最大水平主应力S_(H)为5.1~33.5 MPa,竖向主应力S_(v)为4.2~55.1 MPa,隧道沿线80.48%的区域处于高到极高地应力状态;(2)当隧道埋深小于600 m时,花岗岩隧道主要以水平构造应力为主,应力场类型主要为S_(H)>S_(v)>S_(h),表现应力结构为走滑型;当隧道埋深超过600 m,大埋深的竖向主应力开始占据主导地位,应力场类型主要为S_(v)>S_(H)>S_(h),表现应力结构为正断型;(3)花岗岩隧道地层多为Ⅱ、Ⅲ级硬质脆性围岩,根据岩石弹性能指数和岩石脆性系数测试结果,中粒角闪黑云花岗岩具有中等岩爆倾向的储能和释能条件;(4)基于最大初始地应力值S_(max)和岩石强度应力比R_(c)/S_(max)双指标评价法,花岗岩隧道全长13047 m,其中强烈和极强岩爆风险段共9000 m,占比68.98%;(5)本研究结论可为类似地质条件下的复杂山区深埋长大隧道勘察设计及岩爆灾害防治提供数据支撑。

考虑竖向地温应力的热力耦合瞬态岩爆预测研究

水压致裂法是隧道地质勘查阶段测量地应力的单一手段,受限于水压致裂法未考虑竖向地温应力,加之岩爆预测采用稳态求解,传统岩爆预测手段将会弱化高地温隧道岩爆烈度。利用地勘资料建立康定某隧址区三维数值模型,通过剔除水平主应力中温度应力后进行地应力反演,而后对各反演应力分量叠加地温应力获得初始地应力场并作为岩爆预测模型的应力边界条件,采用Comsol软件热力耦合模块,综合考虑洞壁与洞内环境的对流换热过程和掌子面开挖瞬间的热应力峰值效应,以瞬态求解洞壁应力,得出修正后的岩爆烈度指标。在此基础上,分析传统岩爆预测方法与考虑地温热应力的稳态、瞬态求解方法之间的区别。研究结果表明,依托的隧道工程地温热应力约占水平主应力的20.1%,约占竖向应力的20.5%,忽视地温热应力的存在将会弱化岩爆预测的烈度;考虑地温热应力的稳态岩爆预测烈度较传统岩爆预测方法增强约36.2%,而考虑地温热应力的瞬态岩爆预测烈度继续增强约14.2%;因此,高地温隧道的岩爆预测必须充分考虑地温热应力的叠加效应并以瞬态求解。