Accounting for anisotropic effects in the prediction of the hydro-mechanical response of a ventilated tunnel in an argillaceous rock

In order to investigate the hydro-mechanical (HM) and chemical perturbations induced in an argillaceous formation by forced ventilation during the operational period of a nuclear waste repository, a specific experiment has been performed in a tunnel, at Mont Terri Underground Research Laboratory (URL) in Switzerland. This experiment has been selected in the international project DECOVALEX for model validation and the numerical simulation of this ventilation experiment (VE) is the object of the present paper. Since the argillaceous rock exhibits anisotropic properties, particular attention is given to the evaluation of the effects of various anisotropic features on the predicted results. In situ measurements such as relative humidity (RH), global water mass extracted, pore water pressure, water content, and relative displacements are compared to predictions using both isotropic and anisotropic parameters. Water permeability anisotropy is shown to be the most influencing parameter by far, whereas in situ stress anisotropy has an effect only during the excavation phase. The anisotropy for mechanical parameterization has also some influence, in particular through HM couplings. These HM couplings have the potential to be very significant in terms of providing confidence in describing the experimental observation, and should be considered for further investigation.     

A thermo-hydro-mechano-chemical formulation for modeling water transport around a ventilated tunnel in an argillaceous rock

Argillaceous rocks are being considered as potential host rocks for deep geological disposal. For the research work in DECOVALEX-2011, 5 participant research teams performed simulations of a laboratory drying test and a ventilation experiment for Mont Terri underground laboratory built in argillaceous rock formation. Our study starts with establishing a coupled thermo-hydro-mechano-chemical (THMC) processes model to simulate water transport in rock around the ventilated tunnel. Especially in this THMC formulation, a three-phase and two-constituent hydraulic model is introduced to simulate the processes which occur during tunnel ventilation, including desaturation/resaturation in the rock, phase change and air/rock interface, and to explore the Opalinus clay parameter set. It can be found that water content evolution is very sensitive to intrinsic permeability, relative permeability and capillary pressure in clay rock. Water loss from surrounding rock is sensitive to the change of permeability in clay which is induced by excavation damaged zone. Chemical solute transport in the rock near ventilation experiment tunnel is simulated based on the coupled THMC formulation. It can be estimated that chemical osmotic flow has little significance on water flow modeling. Comparisons between simulation results from 5 teams and experimental observations show good agreement. It increases the confidence in modeling and indicates that it is a good start for fully THMC understanding of the moisture transportation and mechanical behavior in argillaceous rock.     

The excavation of a circular tunnel in a bedded argillaceous rock (Opalinus Clay): Short-term rock mass response and FDEM numerical analysis

The Opalinus Clay formation is currently being investigated as a potential host rock for the deep geological disposal of radioactive waste in Switzerland. Recently, a test tunnel was excavated at the Mont Terri underground rock laboratory (URL) as part of a long-term research project (“Full-scale Emplacement (FE) experiment”) aimed at studying the thermo-hydro-mechanical (THM) effects induced by the presence of an underground repository. The objective of this paper is twofold. Firstly, the results of the rock mass monitoring programme carried out during the construction of the 3 m diameter, 50 m long FE tunnel are presented, with particular focus on the short-term deformation response. The deformation measurements, including geodetic monitoring of tunnel wall displacements, radial extensometers and longitudinal inclinometers, indicate a strong directionality in the excavation response. Secondly, the deformational behaviour observed in the field is analyzed using a hybrid finite-discrete element (FDEM) analysis to obtain further insights into the formation of the excavation damaged zone (EDZ). The FDEM simulation using the Y-Geo code is calibrated based on the average short-term response observed in the field. Deformation and strength anisotropy are captured using a transversely isotropic, linear elastic constitutive law and cohesive elements with orientation-dependent strength parameters. Overall, a good agreement is obtained between convergences measured in the field and numerical results. The simulated EDZ formation process highlights the importance of bedding planes in controlling the failure mechanisms around the underground opening. Specifically, failure initiates due to shearing of bedding planes critically oriented with respect to the compressive circumferential stress induced around the tunnel. Slippage-induced rock mass deconfinement then promotes extensional fracturing in the direction perpendicular to the bedding orientation. The simulated fracture pattern is consistent with previous experimental evidence from the Mont Terri URL.     

岩脉对隧道围岩稳定性影响分析

岩脉是一类特殊的工程岩体,旧堡隧道施工中遇到了辉绿岩和花岗伟晶岩两类岩脉。其中辉绿岩脉在400m埋深处发生了热液蚀变,试验测得其膨胀力为25kPa,自由膨胀率为0.75%,软化系数小于0.12,遇水软化是蚀变带围岩发生大变形的重要原因;花岗伟晶岩脉与围岩呈破碎接触,破碎带岩体呈碎裂结构,属Ⅳ-Ⅴ类围岩,塌方时有发生。通过施工工程地质勘察,查明岩脉工程地质条件是解决相关问题的前提之一,提出以超前地质预报和施工监测作为施工工程地质勘察的两大技术手段。针对辉绿岩脉蚀变带大变形问题,采用了注浆堵水的措施防止围岩大面积淋水软化变形,效果良好。     

天子庙隧道围岩稳定性分析

从传统的地质方法和数值模拟定量评价入手,以天子庙隧道为例,对隧道围岩工程质量进行了综合分级研究,并对地质模型进行了有限元数值模拟计算,为双线长隧道围岩稳定性评价提供了一定的借鉴。     

公路隧道围岩变形分析

针对景婺黄高速公路隧道工程地质条件复杂,不良地质现象及病害严重,路线区域地下水丰富等众多特点,隧道施工过程中对其围岩进行了监控,并对变形过程进行了分析,通过数据分析,改进施工工艺,从而保障了工程施工质量,节约了工程投资。     

基于现场监测的隧道围岩压力分布规律与特征

结合邢汾高速公路隧道现场监测数据,探讨了国内其他隧道围岩压力的统计数据,分析了围岩压力的总体分布规律和围岩压力的时空分布特征,并对衬砌结构的优化提出了建议。     

隧道断层破碎带围岩稳定性影响分析

针对某公路隧道断层破碎带发育情况,分析了影响隧道断层破碎带围岩稳定性因素,并基于有限元MIDAS-GTS分析软件,采用摩尔—库仑模型,对隧道进行了分步开挖数值模拟,研究了断层破碎带处位移特征及应力特征,得出了一些有意义的结论。     

软岩隧道围岩变形分析及处理

从介绍软岩隧道的基本变形特征出发，系统分析了引起软岩隧道变形的原因，全面讨论了软岩隧道的支护原理、原则与方法，并详细介绍了底鼓问题的防治方法，对软岩地质条件下的施工具有重要的现实意义。     

Simulations of THM processes in buffer-rock barriers of high-level waste disposal in an argillaceous formation

The main objective of this paper is to investigate and analyse the thermo-hydro-mechanical (THM) coupling phenomena and their influences on the repository safety. In this paper, the high-level waste (HLW) disposal concept in drifts in clay formation with backfilled bentonite buffer is represented numerically using the CODE_BRIGHT developed by the Technical University of Catalonia in Barcelona. The parameters of clay and bentonite used in the simulation are determined by laboratory and in situ experiments. The calculation results are presented to show the hydro-mechanical (HM) processes during the operation phase and the THM processes in the after-closure phase. According to the simulation results, the most probable critical processes for the disposal project have been represented and analyzed. The work also provides an input for additional development regarding the design, assessment and validation of the HLW disposal concept.     

深埋隧洞围岩应力分析及岩爆预测

采用有限元软件,数值模拟分析了相同侧压系数、不同埋深工况下的深埋隧洞围岩应力变化规律,初步判别了岩爆可能性及岩爆发生部位,对隧洞的设计及施工过程中岩爆的防治具有一定的指导作用。     

某引水隧洞岩溶段裸岩固结灌浆试验施工分析

对锦屏二级水电站引水隧洞岩溶段裸岩固结灌浆试验进行了全面完整的分析和阐述,验证了引水隧洞岩溶段裸岩固结灌浆施工方法、程序及施工工艺的可行性和合理性,为后序大规模的固结灌浆提供了可靠的技术参数和工艺依据。     

全风化岩层中双线盾构上穿近邻地铁隧道影响分析

依托佛莞城际铁路盾构隧道在全风化花岗岩地层中上穿广州地铁七号线工程,针对全风化花岗岩地层致密、渗透系数小及双层四线叠交穿越复杂地层等特点,通过现场监测与三维动态有限元数值模拟手段,解决实际工程中注浆压力合理取值与既有隧道变形控制这两大难题。其中,通过模拟掘进隧道在不同注浆压力值的工况下,对既有隧道动态上浮变形值和地表沉降值的影响关系,进而确定最佳注浆压力值。同时,由于双层四线叠交穿越工况对既有隧道扰动的影响较大,为避免发生管片错台和开裂等危险,结合工程实际提出控制既有隧道变形的措施。研究结果表明：在全风化地层中注浆压力设为0.5MPa时,能合理控制地表沉降与既有隧道变形;穿越施工对既有地铁隧道竖向变形的影响存在“滞后效应”;盾构单线穿越后,既有隧道竖向变形呈现近似单波峰状的正态分布曲线;盾构二次穿越后,曲线形态由近似正态分布曲线向类“M”双波峰形转变,且波峰位置产生约2m的偏移;既有隧道横断面管片最终变形呈“竖鸭蛋”状,其横向椭圆度为1.4‰,竖向椭圆度为0.71‰。针对分析结果,工程中采取合理的压重措施,有效抑制既有隧道的上浮变形,研究成果在隧道穿越类似地层的施工中具有一定的参考价值。     

贵州某隧道浅埋段围岩大变形成因分析

针对贵州某隧道洞口浅埋段在施工过程中出现的围岩大变形情况,在分析断面YK90+479处施工监测数据的基础上,结合地质、设计、施工等因素,分析出围岩破碎、洞身浅埋、上台阶开挖扰动等是造成围岩变形的主要原因。     

隧道下伏岩溶空腔围岩稳定性分析

依托重庆某隧道工程实例,综合地质雷达和超前钻孔两种方法的实际探测结果,采用FLAC软件进行建模,并分析了存在空腔条件下某典型断面竖直方向变形场、最大主应力场和塑性区的计算结果,建议隧道施工过程中应在保证隧道工期的同时,对隧道岩溶空腔灾害进行实时监测和有效处理。     

国内外两种不同的隧道围岩分级方法

结合我国关于公路隧道围岩分类的相关规定，对国内外采用的两种不同的隧道围岩分级方法进行了系统的分析介绍，并分析了各自的优缺点，提出了适合我国公路隧道的围岩分级方法，从而为公路隧道的设计、施工和养护服务。     

松潘高地应力软岩隧道变形预测

以成兰高速铁路松潘隧道高地应力软岩大变形施工段为工程背景,对隧道典型断面D3K246+265的围岩拱顶下沉和水平收敛位移的实际监控量测数据进行回归分析并作曲线拟合,并据此预测围岩的最终变形量,并和断面D3K246+285的最终变形量进行对比验证。结果表明,该种变形预测方法对于赋存在复杂地质环境的高地应力软岩隧道具有较好的可行性,对调整与修正隧道支护设计参数、预留量的大小和保证隧道安全方面具有一定的指导意义。     

Air velocity and concentration of noxious substances in a naturally ventilated tunnel

All internal combustion engines produce exhaust gases containing noxious compounds: carbon monoxide (CO), nitrogen oxides (NO_x), carbon oxides (C_xO_y) and exhaust gases. With the help of the mathematical model the concentrations of some dangerous substances at the end of tunnel with unidirectional traffic were calculated, and were replaced with a criterial number. Corresponding software was developed, which makes it possible to do quick and simple calculations for some concentrations and the criterial number. Finally, presented is a correlation between criterial number and the other parameters as a criterion to determine a threshold between natural and forced ventilation.     

Data-based mechanistic modelling approach to determine the age of air in a ventilated space

In literature, local mean age of air is used as an important index to evaluate indoor air quality in ventilated rooms. In this research, a data-based mechanistic approach is used to model the spatial–temporal mass distribution in an imperfectly mixed forced ventilated installation. A first-order transfer function model has proved to be sufficiently good in describing the mass transfer dynamics $(R_t^2=0.987)$ of the system. Furthermore, it was possible to fully understand the physical meaning of the model parameter. The parameter is found to be an inverse of the age of air. This Data-Based Modelling approach proved to be more robust when dealing with measurement noise. Finally, the modelled age of air was validated with a classical step up determination of the age of air for experimental data. Good correlation $(R_t^2=0.77)$ was found between both results, which proved the physical background of the model parameter.     

南川三泉隧道软化围岩法防治岩爆效果的研究

以三泉隧道为研究背景,通过数值模拟和现场试验,探讨了钻爆法施工中喷水软化围岩防止岩爆的效果,结果表明,围岩喷水软化后,降低了围岩的强度和切向应力,释放了围岩的应变能并降低了岩爆发生的等级。