A displacement-based back-analysis method for rock mass modulus and horizontal in situ stress in tunneling – Illustrated with a case study

This paper presents a displacement based back-analysis method for the determination of rock mass modulus (E) and the horizontal in situ stress (P) perpendicular to the axis line of the tunnel excavation in hard and intact rock masses. The rock mass is assumed to respond in an isotropic and linear elastic manner. Essentially, the method is a best-fit solution of back-analysis by comparing the measured displacements near a tunnel face during excavation with those calculated using a three-dimensional finite element method. The method can be applied efficiently and effectively by iterative algorithms such as direct search technique and damping least square technique. In particular, a three-dimensional finite element pattern technique (3-D FEPT) is used to compute the theoretical displacements for saving computation time. The method is further illustrated with a case study. The case study deals with a test adit at Zhanghewan Pumped Storage Power Station in Hebei Province, North China. It is shown that the back-analyzed results of E and P are reliable and representative for the actual rock masses.     

位移反分析计算在隧道施工中的应用

通过对东山隧道现场量测得到水平收敛及拱顶下沉的数值分析,利用ANSYS有限元法程序模拟围岩初始应力场,初始应力场代替自重应力场数值模拟隧道开挖,通过计算,评价支护结构的稳定性,优化支护结构体系。     

Measurement and interpretation of long-term deformation of a rock slope at the Ikura limestone quarry,Japan

More than 10 years of displacement measurements at the Ikura limestone quarry in Japan have clarified aspects of rock slope deformation arising from excavation in the quarry. Although the cause of most deformations can be explained theoretically, those occurring in a rock slope just behind the Tarumi working face proved perplexing. Contraction continued to occur on the rock slope although excavation of limestone had ceased at this face. The cause of this continuous deformation was evaluated through numerical analysis employed to assess the stability of the rock slope. An automatic 3D mesh generation technique was used to model the complex topography of the quarry resulting from the excavation and a finite element mesh model was rendered for each of the successive excavation stages. Elastic analysis then allowed the resulting rock slope deformation to be predicted. The calculated results reveal that the rock slope continued to deform elastically after excavation had ceased on the Tarumi face and that the on-going excavation at the Kawamukai working face, located 400 m away from the rock slope, was the probable cause. The calculated results using appropriate elastic moduli were in good agreement with measured results. The rock slopes are assessed as stable and the continuous deformation is believed to be elastic.     

断层滑动准则和稳定性评价及构造应力场的反演

 为研究矿震、突出等动力现象与断层滑动、开采深度的关系,首先在试验室进行砂岩双剪摩擦试验,从工程角度出发,确定砂岩的滑动准则。其次为研究地下岩体的稳定性,确定构造应力场的分布,针对地下岩体的赋存特点,在分析实测应力分布特点的基础上,通过地质动力区划方法建立地质构造模型,采用有限元法反演复杂断层扰动下的构造应力场,计算结果与矿区震源面制分析结果以及原岩应力测量结果取得较好的一致性。计算的高应力区域中心位置位于I级断裂的不连续地带,与地下地震多发地带相对应,说明构造应力是矿区地震的主要成因。研究表明,断裂面的失稳滑动是北票矿区地震的主要机制,构造应力的存在是矿震发生的必要条件,而矿区开采则是发震的诱导因素,北票断裂对区域其他次级断裂及其构造应力区起主导和控制作用,是北票矿区动力现象的动力源。     

深孔水压致裂地应力测量及应力场反演分析

 万福煤矿是一座拟建特大型矿井,上覆冲积层厚度高达700 m,主煤层平均埋深达1 004.12 m。选择7个勘探钻孔、37个试验段进行深孔水压致裂地应力测量。为保证超千米深孔地应力测量的成功,对传统水压致裂法的测试技术和设备进行改进,提高系统的耐压能力和测试精度。测孔最大水平主应力与垂直主应力的比值较大,平均为1.97,说明勘探区现今应力场以水平应力为主导。测得的21个印模中有18个点位于NEE-SWW向,3个点位于NW-SE向,符合本区震源机制解得出的挤压应力场方向,且与新构造活动所反映的区域构造应力场方向一致。结合实际的地质条件和地层参数,在实测地应力结果的基础上,提出基于有限元三维地应力拟合分析法反演勘探区现今地应力场,给出煤层顶板主应力分布曲线并分析井下可能出现的各类不良地质现象。     

Estimation of the three-dimensional in situ stress field around a large deep underground cavern group near a valley

Understanding three-dimensional(3D) in situ stress field is of key importance for estimating the stability of large deep underground cavern groups near valleys.However,the complete 3D in situ stress fields around large deep underground cavern groups are difficult to determine based on in situ stress data from a limited number of measuring points due to the insufficient representativeness and unreliability of such measurements.In this study,an integrated approach for estimating the 3D in situ stress field around a large deep underground cavern group near a valley is developed based on incomplete in situ stress measurements and the stress-induced failures of tunnels excavated prior to the step excavation of the cavern group.This integrated approach is implemented via four interrelated and progressive basic steps,i.e.inference of the regional tectonic stress field direction,analyses of in situ stress characteristics and measurement reliability,regression-based in situ stress field analysis and reliability assessment,and modified in situ stress field analysis and reliability verification.The orientations and magnitudes of the3D in situ stress field can be analyzed and obtained at a strategic level following these four basic steps.First,the tectonic stress field direction around the cavern group is deduced in accordance with the regional tectonic framework and verified using a regional crustal deformation velocity map.Second,the reliability of the in situ stress measurements is verified based on the locations and depths of stressinduced brittle failures in small tunnels(such as exploratory tunnels and pilot tunnels) within the excavation range of the cavern group.Third,considering the influences of the valley topography and major geological structures,the 3D in situ stress field is regressed using numerical simulation and multiple linear regression techniques based on the in situ stress measurements.Finally,the regressed in situ stress field is further modified and reverified based on the stress-induced brittle failures of small tunnels and the initial excavation of the cavern group.A case study of the Shuangjiangkou underground cavern group demonstrates that the proposed approach is reliable for estimating the 3D in situ stress fields of large deep underground cavern groups near valleys,thus contributing to the optimization of practical excavation and design of mitigating the instability of the surrounding rock masses during step excavations.     

主应力演化影响下的深部巷道围岩变形破坏特征试验研究

研究主应力变化对深部巷道围岩变形破坏特征的影响是巷道支护中非常必要的。以某矿处于深部高水平应力条件下的巷道围岩为工程背景,以大尺度三维相似材料模拟试验系统和制作的主方向应力传感器量测工具,采用"先加载后卸载"的开挖方式模拟主应力大小和方向演化影响下的有支护巷道围岩产生剪切滑移的变形破坏特征。研究表明,在高水平应力环境下巷道在掘进开挖过程中顶底板受挤压剪切作用产生变形破坏,破坏范围呈现"楔形"渐进发展;通过模型剖切面发现巷道围岩顶底板产生了不同数量的对称螺旋状剪切滑移裂缝,并向巷道两帮发展并交叉,将巷道围岩形成一定范围的剪切破坏区域;通过分析主应力大小及方向的演化可知,巷道围岩受高水平应力作用形成的剪切滑移裂缝破坏与主应力大小及方向演化存在必然联系,认为最小主应力的调整对剪切滑移裂缝的形成起到了重要作用。     

长江三峡工程永久船闸中隔墩岩体变形分析及预测

采用综合方法对长江三峡工程永久船闸二闸室至三闸首部分的中隔墩岩体变形规律进行了分析及预测。首先,运用离散单元法与有限单元法等数值模拟方法分析了该段中隔墩岩体分别在施工期和运行期的变形规律。然后,在监测数据的基础上,采用时间序列和灰色系统方法预测了岩体的变形趋势。综合分析结果表明:垂直于闸室轴线的水平位移在开挖完成后基本处于稳定状态,而在运行期有所减少;平行于闸室轴线的水平位移总体向下游发展;而垂直方向的位移先表现为回弹,后发生沉降。     

水电站地下厂房开挖过程弹塑性数值分析

采用三维弹塑性有限元计算,对某水电站地下厂房开挖过程进行了数值模拟,分析了开挖过程中毛洞周边围岩位移和应力的变化规律,分析结果表明厂房由于洞室围岩比较破碎,围岩开挖变形量较大,洞室的稳定性较差,开挖后要及时施工支护结构。     

薄壁面板隔墙法在特大断面隧道施工中的力学特征分析

以某浅埋暗挖城市地铁车站为工程背景,利用有限元数值模拟方法分析了薄壁面板隔墙法的原理和在施工过程中隧道围岩的变形和力学演化特征。分析结果表明,薄壁面板隔墙法的台阶式导坑开挖主导了隧道结构的应力集中特征和变形特征,施工时特大断面隧道的初衬、锚杆和围岩的应力、应变均沿隧道轴向方向阶段性地出现多个应力集中区和位移剧变区,各区域的分界处基本和隧道先开挖侧各导坑开挖端面平齐。而且,中隔墙和预留核心土的设置有效地改善了开挖对特大断面隧道围岩的扰动,使得隧道围岩塑性区小,隧道的拱脚水平相对净空变化指标和拱顶相对下沉指标均能满足特大断面隧道的稳定性要求。     

大型金属矿体开采地应力场变化及其对采区岩体移动范围的影响分析

根据金属矿地下开采引起的地应力场变化对岩体移动变形范围影响的工程实际，采用现场实测和数值分析方法，对深埋破碎金属矿体开采引起的地应力场变化及其对地质环境影响并导致岩体移动变形范围不断扩大这一客观现象进行了具体计算分析。结果表明，矿体开采后，随着采深的增加地应力明显增大，岩体移动变形的影响范围也随之而增大。另一方面，地应力场变化，尤其是水平方向的构造应力场变化和影响是不可忽视的。     

高地应力深部巷道开挖锚固特性的三维地质力学模型试验研究

为研究锚固支护条件下深部巷道围岩是否产生分区破裂以及岩锚支护对分区破裂的影响,以淮南矿区丁集煤矿深部巷道为工程背景,进行了锚固支护条件下高地应力深部巷道开挖三维地质力学模型试验。通过模型试验发现围岩应变呈现波浪形变化规律以及洞周锚杆受力出现拉压交替变化现象。通过与未加锚支护模型试验结果的对比,揭示锚杆对抑制巷道围岩分区破裂具有重要的作用,这为深入分析深部巷道开挖锚固特性和优化深部巷道支护设计奠定了坚实的试验基础。     

构皮滩水电站升船机边坡开挖稳定性分析

以现场地质勘查及室内试验研究成果为基础,采用有限元软件模拟了构皮滩水电站第三级升船机边坡的开挖施工过程,通过对比分析三种不同支护开挖方案条件下边坡的变形形态、最大主应力分布及塑性区分布规律,研究了边坡的开挖稳定性,得到以下结论:锚杆和锚索的支护方案能有效控制局部失稳区域的位移变形形态;锚杆和锚索支护方案能有效控制边坡坡面开挖后的拉应力区;锚杆、锚索支护均能有效控制边坡开挖后的塑性区面积及分布;锚杆和锚索同时施加的支护方案能较好的保障第三级升船机边坡的开挖稳定性。     

基于有限元理论的深路堑边坡稳定性分析

基于有限元理论,采用岩土工程应力应变分析软件SIGMA/W,分别对深路堑边坡开挖前后的应力应变特性进行数值模拟,结果表明:开挖前后边坡处于稳定状态。用极限平衡法所计算的稳定性安全系数进行验证,结果表现为一致性,边坡整体较稳定,开挖时坡顶可能发生浅表滑移。此结果为公路建设提供了依据。     

深埋地下车站双岩柱开挖方法的模拟研究

基于新建京张铁路八达岭地下车站超大跨的特点,研究其大埋深和大跨度开挖时采用双岩柱法的围岩和支护力学性能。车站埋深达75 m~110 m,跨度43.87 m,高度21.7 m,长度495 m,断面面积为857.102 6 m²,如此大的地下车站在国内尚属首例,世界罕见。采用大型非线性有限元软件ABAQUS模拟计算双岩柱法开挖和支护全过程,得出每一开挖步围岩应力,锚杆轴力,衬砌应力,围岩变形的力学参数。计算结果表明,岩柱在开挖过程中发挥了充分的作用,对围岩应力,拱顶沉降起到了非常好的作用,使得地表沉降控制在合理的范围内,说明设计方案比较合理,双岩柱法在较好的围岩中对施工具有快捷和维护围岩稳定的作用。     

糯扎渡水电站#2导流洞三维非线性有限元反分析

糯扎渡水电站#2导流隧洞开挖经过F3断层,开挖过程中,F3断层影响带附近的岩体力学参数直接控制着围岩的变形和应力分布。为了评判后续Ⅱ、Ⅲ层开挖围岩的稳定性,需要反演出F3断层附近围岩的岩体力学参数和初始地应力场。对于隧洞开挖反分析问题,考虑到现场位移监测数据与隧洞开挖之间的相互关系,采用开挖位移增量形式进行反分析,并且分析了三维非线性有限元以开挖位移增量的均方误差作为目标函数的反分析计算过程。为了减少现场的位移量测数据对反分析结果的影响,改善其规律性,采用多元线性回归模型对位移监测数据进行整理,有效的提高了反分析计算结果的精度。最后,利用上述方法反演得到了#2导流隧洞F3断层附近岩层的岩体力学参数和初始地应力场。     

高应力软岩近距离巷道工程的掘进扰动与稳定性

针对高应力近距离巷道工程的开挖掘进及稳定性问题,进行了理论分析、数值计算及现场监测等一系列研究。首先,在某矿山深部巷道工程的地质与施工条件基础上,采用理论方法分析了掘进爆破扰动应力传播规律及其对邻近巷道或硐室围岩稳定性的影响,并给出了扰动波在岩体中的衰减方程。然后,根据相关理论,采用FLAC软件进行了一次爆破掘进长度和开挖工序等掘进方案的数值分析,结果表明：在动荷载（爆破掘进）作用下,由施工巷道开挖时所产生的变形会直接影响到邻近硐室或巷道周边岩体,应力释放区域较大；当一次爆破掘进长度较小时,由于整段巷道的扰动次数较多而会引起变形增大,但初始速度较小,则反之。最后,采用监测的方式,对施工巷道进行了开挖扰动分析,结果表明：相距为20 m左右的两条巷道,开挖爆破扰动程度较大区域在后掘巷道掘进工作面的前后10～20 m范围之内,而对本条巷道扰动程度较大范围一般距掘进工作面25 m左右；并按照扰动程度大小可分为破坏区、影响程度较大区和影响程度较小区,破坏区和影响区一般位于掘进面30 m以内。     

深井巷道掘进围岩演化特征模拟与扰动应力场分析

 深井巷道围岩扰动应力场与开挖扰动区的形成密切相关。然而,受现场地质条件和监测技术制约,尚难以准确获得围岩扰动应力的演化过程。为此,首先通过原位监测得到深井巷道围岩开挖扰动区的演化特征;然后,基于监测结果利用反分析的方式构建能较为准确地模拟围岩开挖扰动区演化特征的数值模型;最后,通过这一模型分析了深井巷道掘进过程中围岩扰动应力场的演化特征。研究结果表明：当工作面未掘进至监测断面时,由于工作面前方岩体空间约束,测点应力值基本没有变化;当工作面掘进过监测断面后,巷道帮部、顶底板的主应力大小和方向均发生了变化;通过对比扰动应力场与原位监测得到的开挖扰动区的演化特征,发现两者的部分演化特征较为相似。     

Influence of stress path on tunnel excavation response – Numerical tool selection and modeling strategy

The actual stress path in a rock mass during tunnel excavation is complex. To capture the correct tunnel excavation response, it is important to correctly resemble the stress path in situ in the numerical tools.FLAC and Phase² are two powerful two-dimensional continuum codes for modeling soil, rock, and structural behavior, in the fields of geotechnical, geomechanics and in civil and mining engineering. FLAC is based on explicit finite difference formulation while Phase² is based on implicit finite element formulation. When the two codes are applied to the analysis of tunnel excavation problems, difference in results might occur simply due to the different formulation methodologies used in these codes. It is shown that for linear elastic tunnel excavation problems, both codes provide the same result because stress path is unimportant. For tunnel excavation in elasto-plastic materials using long-round drill and blast method, there is significant difference in terms of yielding zone distribution by the two codes if conventional modeling approach is used, especially when the rock strength is low relative to the in situ stress magnitude. The mechanism of the difference is investigated and recommendation provided for choosing appropriate tools and modeling strategies for tunnel excavation problems. The importance of honoring the true stress path in tunnel excavation response simulation is illustrated using a few examples.     

围岩卸载损伤演化及应力场调整有限元分析

隧道、洞室等地下工程的修建过程 ,是洞室壁面附近围岩不断发生应力卸载的过程。在这一过程中围岩力学性质与加载过程中表现出的力学性质存在一定的差别。本文通过引入服从韦伯分布函数的细观岩石微元体 ,运用连续介质损伤力学理论 ,得出了可以反映岩石非均匀性的本构关系式 :然后运用岩石破裂与失稳过程RFPA分析系统 ,对隧道、洞室等地下工程由于洞室开挖引起的围岩卸载过程中 ,洞室孔壁附近围岩发生的损伤演化和应力场调整全过程进行了有限元分析 ,得到了洞室壁面附近围岩损伤演化和应力场调整过程图。