Mechanism of zonal disintegration phenomenon in enclosing rock mass around deep tunnels

In order to study the mechanism of the zonal disintegration phenomenon (ZDP), both experimental and theoretical investigations were carried out. Firstly, based on the similarity law, gypsum was chosen as equivalent material to simulate the deep rock mass, the excavation of deep tunnel was modeled by drilling a hole in the gypsum models, two circular cracked zones were measured in the model, and ZDP in the enclosing rock mass around deep tunnel was simulated in 3D gypsum model tests. Secondly, based on the elasto-plastic analysis of the stressed-strained state of the surrounding rock mass with the improved Hoek-Brown strength criterion and the bilinear constitutive model, the maximum stress zone occurred in vicinity of the elastic-plastic interface due to the excavation of the deep tunnel, rock material in maximum stress zone is in the approximate uniaxial loading state owing to the larger tangential force and smaller radial force, the mechanism of ZDP was explained, which lay in the creep instability failure of rock mass due to the development of plastic zone and transfer of the maximum stress zone within the rock mass. Thirdly, the analytical critical depth for the occurrence of ZDP was obtained, which depended on the mechanical indices and stress concentration coefficient of rock mass. Foundation item: Projects(50525825, 90815010) supported by the National Natural Science Foundation of China; Project(2009CB724608) supported by the Major state Basic Research Development Program of China     

Zonal disintegration phenomenon in enclosing rock mass surrounding deep tunnels -- Elasto-plastic analysis of stress field of enclosing rock mass

The zonal disintegration phenomenon (ZDP) is a typical phenomenon in deep block rock masses. In order to investigate the mechanism of ZDP, an improved non-linear Hock-Brown strength criterion and a bi-linear constitutive model of rock mass were used to analyze the elasto-plastic stress field of the enclosing rock mass around a deep round tunnel. The radius of the plastic region and stress of the enclosing rock mass were obtained by introducing dimensionless parameters of radial distance. The results show that tunneling in deep rock mass causes a maximum stress zone to appear in the vicinity of the boundary of the elastic and the plas-tic zone in the surrounding rock mass. Under the compression of a large tangential force and a small radial force, the rock mass in the maximum stress zone was in an approximate uniaxial loading state, which could lead to a split failure in the rock mass.     

Mechanism of Pendulum-type wave phenomenon in deep block rock mass

Pendulum-type (μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse waves propagated in continuum media and is also a phenomenon of the sign-variable reaction of deep block rock masses to dynamic actions, besides the Anomalous Low Friction (ALF) phenomenon. In order to confirm the existence of the μ wave and study the rule of variation of this μ wave experimentally and theoretically, we first carried out one-dimensional low-speed impact experiments on granite and cement mortar blocks and continuum block models with different characteristic dimensions, based on the multipurpose testing system developed by us independently, The effects of model material and dimensions of models on the propagation properties of 1D stress wave in blocks medium are discussed. Based on a comparison and analysis of the propagation properties (acceleration amplitudes and Fou-rier spectra) of stress wave in these models, we conclude that the fractures in rock mass have considerable effect on the attenuation of the stress wave and retardarce of high frequency waves. We compared our model test data with the data of in-situ measurements from deep mines in Russia and their conclusions. The low-frequency waves occurring in blocks models were validated as Pendu-lum-type wave. The frequencies corresponding to local maxima of spectral density curves of three-directional acceleration satisfied several canonical sequences with the multiple of (√2),most of those frequencies satisfied the quantitative expression(√2)iVP/2△.     

Elastoplastic model for discontinuous shear deformation of deep rock mass

Deep rock mass possesses some unusual properties due to high earth stress,which further result in new problems that have not been well understood and explained up to date.In order to investigate the deformation mechanism,the complete deformation process of deep rock mass,with a great emphasis on local shear deformation stage,was analyzed in detail.The quasi continuous shear deformation of the deep rock mass is described by a combination of smooth functions:the averaged distribution of the original deformati...     

New methods of safety evaluation for rock/soil mass surrounding tunnel under earthquake

The objective of this work is to obtain the seismic safety coefficient and fracture surface and proceed with the seismic safety evaluation for the rock mass or soil mass surrounding a tunnel,and the limitation of evaluating seismic stability is considered using the pseudo-static strength reduction.By using the finite element software ANSYS and the strength reduction method,new methods of seismic safety evaluation for the rock mass or soil mass surrounding a tunnel are put forward,such as the dynamic finite element static shear strength reduction method and dynamic finite element shear strength reduction method.In order to prove the feasibility of the proposed methods,the results of numerical examples are compared with that of the pseudo-static strength reduction method.The results show that 1） the two methods are both feasible,and the plastic zone first appears near the bottom corners; 2） the safety factor of new method Ⅱ is smaller than that of new method I but generally,and the difference is very small.Therefore,in order to ensure the safety of the structure,two new methods are proposed to evaluate the seismic stability of the rock mass or soil mass surrounding a tunnel.A theoretical basis is provided for the seismic stability of the rock mass or soil mass and the lining surrounding a tunnel and also provided for the engineering application.     

基于马尔可夫过程和深度神经网络的TBM围岩识别

为了实现隧道围岩的实时识别,基于马尔可夫过程和深度神经网络模型,提出将先验围岩信息和掘进参数结合,作为深度神经网络输入的隧道掘进机（TBM）围岩实时识别方法. 根据施工现场地质勘探资料,用马尔可夫过程的隧道围岩分类方法预测隧道沿线的围岩分布概率;将该围岩分布概率作为先验围岩信息,结合TBM掘进参数作为神经网络输入,真实围岩类别作为输出,训练深度神经网络以实现对TBM前方围岩的实时识别. 使用工程现场数据进行对比实验,结果表明,所设计的深度神经网络模型的围岩总体识别率高于96%. 相比于仅将掘进参数作为输入,当结合先验围岩信息和掘进参数作为输入时,模型围岩识别率提高6%以上.     

Failure precursor of surrounding rock mass around cross tunnel in high-steep rock slope

The stability of the surrounding rock mass around cross tunnel in the right bank slope of Dagangshan hydropower station, in the southwestern China, was analyzed by microseismic monitoring as well as numerical simulations. The realistic failure process analysis code (abbreviated as RFPA3D ) was employed to reproduce the initiation, propagation, coalescence and interactions of micro-fractures, the evolution of associated stress fields and acoustic emission (AE) activities during the whole failure processes of the surrounding rock mass around cross tunnel. Combined with microseismic activities by microseismic monitoring on the right bank slope, the spatial-temporal evolution and the micro-fracture precursor characteristics during the complete process of progressive failure of the surrounding rock mass around cross tunnel were discussed and the energy release law of the surrounding rock mass around the cross tunnel was obtained. The result shows that the precursor characteristic of microfractures occurring in rock mass is an effective approach to early warn catastrophic damage of rock mass around cross tunnel. Moreover, the heterogeneity of rock mass is the source and internal cause of the failure precursor of rock mass.     

Zonal disintegration phenomenon in enclosing rock mass surrounding deep tunnels—mechanism and discussion of characteristic parameters

The mechanism of the zonal disintegration phenomenon (ZDP) was realized based on the analysis of the stressedstrained state of the rock mass in the vicinity of the maximum stress zone, which resides in the creep instability failure of rock mass due to the development of a plastic zone and transfer of the maximum stress zone within the rock mass. Some characteristic parameters of the ZDP are discussed theoretically. In first instance, the analytical critical depth condition for the occurrence of ZDP was obtained, which depends on the characteristics and stress concentration coefficient of the rock mass. Secondly, based on creep theory, the expression of the outer radius of the undisturbed zones in the deep rock mass was obtained with the use of an improved Burgers theological model, which indicated that the radius depends on the characteristics of the rock mass and the depth of excavation and increases quasi-linearly with the rise of creep compliance of the rock mass. Finally, the formula for the distance of the most remote fissured zone away from the working periphery was derived, which increases logarithmically with the increase in the ratio of the in-situ stress and ultimate strength of rock mass. The distances between fissured zones are discussed in qualitative terms.     

南水北调西线工程深埋隧洞岩爆与地应力研究

在分析深埋隧洞岩爆破坏机制和地应力条件的同时 ,详细论述了南水北调西线工程主要引水线路区的现代构造应力场特征及主应力的大小、相互关系 ;根据地应力、岩性等特征初步评价主要引水线路区隧洞围岩发生岩爆的可能性     

某岩溶隧道围岩稳定性及涌水量预测的流固耦合分析

以沪蓉西高速公路乌池坝隧道为工程背景,建立了岩溶隧道三维地质模型,分析了在流固耦合条件下隧道轴向和垂直隧道轴向方向上的隧道围岩应力特征,讨论了围岩应力与分析断面距暗河、地表岩溶洼地之间距离以及与工况之间的关系,分析了各种工况条件下隧道典型断面洞壁的位移变化情况,对隧道的涌水量进行了分析和预测.研究和分析结果可为岩溶地区隧道的围岩稳定性分析和涌水量预测提供参考和帮助.     

双节理岩体TBM滚刀破岩过程数值模拟

为了研究节理特征对全断面掘进机(tunnel boring machine, TBM)盘形滚刀破岩的影响,采用颗粒流方法建立盘形滚刀与含平行双节理岩体的二维数值模型,进行不同节理倾角和间距的30组数值试验,根据数值试验结果研究岩体破裂模式、滚刀竖向接触力峰值随节理倾角和间距的变化规律、滚刀破岩过程中细观裂纹扩展规律。研究结果表明:不同的节理特征下,滚刀破岩可以分为4种基本的破裂模式;滚刀竖向接触力峰值随节理倾角的增大呈现先减小后增大的趋势,在节理倾角为30°或45°时最小,在节理倾角为90°时最大;滚刀竖向接触力峰值随节理间距的增大总体上呈现增大趋势;随滚刀的贯入,滚刀竖向接触力与细观裂纹个数有3个关联的变化阶段。通过研究TBM滚刀与节理岩体相互作用机制,揭示不同节理特征对滚刀破岩的影响规律,对TBM滚刀的合理设计和施工有一定的指导意义。     

深部巷道围岩变形试验与数值模拟研究

为了研究深部软岩巷道的变形破坏特性,以淮南矿区某煤矿13-1煤回采巷道为例,在现场调查回采巷道工程概况的基础上,开展了室内深部回采巷道围岩变形特性相似模拟试验,并基于块体离散元法,建立了深部回采巷道围岩的数值模型,模拟了开挖过程中围岩的变形特性。相似模拟试验和数值模拟试验结果表明,深部巷道围岩的典型特征为:巷道底臌量两帮移近量顶板下沉量,巷道不同围岩受开挖扰动的位移影响范围不同,底板为3.5 m,顶板为2.45 m,两帮为5.5 m。     

黏弹性节理岩体中应力波的传播特性分析

为探究黏弹性节理对应力波在岩体中传播规律的影响,引入饱依丁-汤姆逊模型作为位移不连续条件,基于时域递归方法推导出应力波通过一组平行黏弹性节理的传播方程;通过将饱依丁-汤姆逊模型退化为Maxwell模型和Kelvin模型所得的时域递归数值解与已有的频域内封闭解对比,验证推导过程的正确性;最后,对相关参数的影响规律进行分析。结果表明：模型无量纲系数、无量纲节理厚度、无量纲节理间距和入射角等都对波的传播产生影响;对于单条节理,应力波的透反射系数以及能量耗散率主要取决于位移不连续模型的无量纲参数、入射角及无量纲节理厚度;而对于一组平行节理,透射系数还和平行节理数与节理间距的大小有关,且节理条数的增加对入射临界角位置处透射波振幅的衰减影响更为明显。     

边坡工程中卸荷岩体的探讨

岩体卸荷是水利水电工程建设中常见的工程地质问题,岩体卸荷裂隙是影响边坡岩体稳定性的重要因素.文章介绍了边坡工程中卸荷岩体的形成机理、裂隙类型、分带依据及卸荷岩体加固时应注意的问题.     

Influence of underground water seepage flow on surrounding rock deformation of multi-arch tunnel

Based on a typical multi-arch tunnel in a freeway, the fast Lagrangian analysis of continua in 3 dimensions（FLAC^3D） was used to calculate the surrounding rock deformation of the tunnel under which the effect of underground water seepage flow was taken into account or not. The distribution of displacement field around the multi-arch tunnel, which is influenced by the seepage field, was gained. The result indicates that the settlement values of the vault derived from coupling analysis are bigger when considering the seepage flow effect than that not considering. Through the contrast of arch subsidence quantities calculated by two kinds of computation situations, and the comparison between the calculated and measured value of tunnel vault settlement, it is found that the calculated value（5.7-6.0 mm） derived from considering the seepage effect is more close to the measured value（5.8-6.8 mm）. Therefore, it is quite necessary to consider the seepage flow effect of the underground water in aquiferous stratum for multi-arch tunnel design.     

地下洞室连续围岩岩爆定量预测模型

根据能量平衡理论,推导了岩爆能量公式,定量分析了地下洞室连续围岩岩爆区位置、面积及碎块弹射速度的影响因素。研究结果表明,围岩水平应力与竖向应力比值小于1,岩爆区面积和碎块平均弹射速度随侧压力系数增大而减小,否则反之。岩爆区面积随岩体峰值荷载前后模量比率系数、岩石颗粒直径、裂隙密度和岩石断裂韧度增大而减小,随泊松比增大而增大。碎块平均弹射速度随颗粒直径、泊松比和岩体峰值荷载前后模量比率系数的增大而减小,随岩石断裂韧度的增大而增大,随裂纹密度的增加先增加后减小最终趋于稳定值。     

裂隙岩体渗流场与应力场耦合数学模型的研究

首先研究裂隙岩体中应力场改变对地下水渗流场的影响作用机理,推导出渗透系数k和给水度μ受应力影响的表达式,进而分析渗流场的变化,地下水的作用引起应力场环境变迁,导致裂隙岩体的渗透变形,在此基础上建立了裂隙岩体中应力场与渗流场耦合作用研究工作程式和具"点荷载"特征的等效连续介质耦合数学模型,并应用于一隧道工程实例进行了计算.     

Rules for confidence intervals of permeability coefficients for water flow in over-broken rock mass

Based on the steady-state seepage method,we used the Mechanical Testing and Simulation 815.02 System and a self-designed seepage instrument for over-broken stone to measure seepage properties of water ...     

Measurement and study of the distributing law of in-situ stresses in rock mass at great depth

To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeless packers, and a multichannel real-time data acquisition system was used for in-situ stresses measurement at great depths （over 1000 m） in a coalfield in Juye of Northern China. The values and orientations of horizontal principal stresses were determined by the new system. The virgin stress field and its distributing law were decided by the linear regression from the logged 37 points in seven boreholes. Besides, the typical boreholes arranged in both the adjacent zone and far away zone of the faults were analyzed, respectively. The results show that a stress concentration phenomenon and a deflection in the orientation of the maximal horizontal stress exist in the adjacent zone of the faults, which further provides theoretical basis for design and optimization of mining.