Hydro-mechanical modelling of the excavation damaged zone around an underground excavation at Mont Terri Rock Laboratory

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed around underground excavations in indurated clay. The stress perturbation around the excavation could lead to a significant increase of the permeability, related to diffuse and/or localised crack propagation in the material. The main objective of this study is to model these processes at large scale in order to assess their impacts on the performance of radioactive waste geological repositories. This paper concerns particularly the hydro-mechanical modelling of a long-term dilatometer experiment performed in Mont Terri Rock Laboratory in Switzerland. The proposed model defines the permeability as a function of the aperture of the cracks that are generated during the excavation. With this model, the permeability tensor becomes anisotropic. Advantages and drawbacks of this approach are described using the results of the Selfrac long-term dilatometer experiment.     

偏压状态下隧道洞口段明洞暗挖施工技术

通过对明洞暗挖施工技术特点及施工技术原理、施工技术要点进行分析,可以有效确保隧道施工的安全顺利开展,并有效地改善施工的质量,同时减少对于环境的破坏和保证施工活动的安全开展,希望能够为我国隧道洞口段施工的顺利进行提供参考,以更好的推动我国隧道施工技术的发展。     

超浅埋隧道暗挖施工模拟

结合浙江省上三线任胡岭隧道超埋段复杂的地质条件，在明控不合理的情况下，采用了挖孔桩系梁帷幕暗挖的施工方案，并利用有限元方法对该方案进行了模拟分析，保证了施工的顺利进行。实践证明，该方法相对明挖是成功的，可行的，节省了投资，缩短了工期，为超浅埋隧道的施工提供了一种新的方法。     

Assessment of excavation damaged zone using a micromechanics model

It is well known that acoustic emission (AE) and microseismic (MS) events are indicators of rock fracturing or damage as the rock is brought to failure at high stress. By capturing the microseismic events, underground excavation induced rock mass degradation or damage can be located. The use of microseismic method has been shown as a valuable tool in a number of nuclear waste repository research programs to monitor the extent of the excavation damaged zone (EDZ), but most of the works are limited to a qualitative assessment.This paper presents a study on the quantification of the degree of damage, in terms of crack density calculated from the crack length, and the extent, in terms of crack density distribution, from microseismic event monitoring data. The approach builds on the finding that a realistic crack size corresponding to a microseismic event can be established by applying a tensile cracking model instead of the traditional shear model, commonly used in earthquake data analysis. It can be shown that brittle rock failure is the result of tensile crack initiation, propagation, accumulation, and interaction. Tensile stress can be generated in a confined rock with heterogeneous material properties. When a crack is formed by tensile cracking in this fashion, its orientation tends to become parallel to the direction of maximum compressive stress. A method is developed to take microseismic event monitoring data as input to determine the damage state and the extent of the EDZ by crack distribution. Based on the crack orientation and crack density information, the rock is modeled by a micro-mechanics based constitutive model which considers the anisotropic material properties. Numerical examples are presented using field monitoring data from a tunnel in granite to demonstrate how microseismicity can be quantitatively linked to dynamic rock mass properties.     

谈浅埋暗挖隧道施工技术

以重庆市轨道交通地铁车站暗挖施工为例,根据工程地质条件及施工特征,阐述了浅埋暗挖隧道的施工工序,并对地铁站的双侧壁导坑法施工中的关键技术措施作了介绍,为类似工程施工提供了技术支持。     

隧道浅埋下穿居民区暗挖法施工参数研究

结合具体工程实例,通过介绍洞顶地形地貌、地质情况、现有施工资源、工期等因素,对预先设定的暗挖施工参数进行具体实施,并经现场验证和修正,最终选取安全可靠、经济方便的施工措施。     

暗挖隧道爆破开挖质量控制研究

暗挖隧道爆破开挖施工过程中,保持良好的开挖质量,无论从成本控制角度还是工期角度,都具有重要的意义。以深圳地铁8号线望基湖停车场入场线隧道为例,对影响隧道开挖质量的条件展开分析,通过运用光面爆破技术以及加强现场施工质量管理等手段,最大程度的减少超欠挖,有效的提升了隧道的开挖质量,可为同类隧道开挖施工提供借鉴。     

基坑开挖对地下通道结构影响的数值模拟分析

通过数值分析,模拟上海地区基坑开挖对已建地下通道结构的影响,分别考虑地下通道正常使用状态下和基坑支撑荷载作用下两种不同工况,分析不同工况荷载对地下通道箱型结构的影响,分析发现基坑支撑荷载对地下通道结构有一定影响,但在地下通道承载能力范围内,说明拟建基坑项目利用地下通道是可行的,为后续相关工程设计提供一定参考。     

Numerical simulation of the excavation damaged zone around an opening in brittle rock

The micromechanics-based damage model proposed by Golshani et al. [A micromechanical model for brittle failure of rock and its relation to crack growth observed in triaxial compression tests of granite. Mech Mater 2006;38:287–303] is extended so that time-dependent behavior of brittle material can be taken into account, with special attention to the numerical analysis of an excavation damaged zone (EDZ) around an opening, which is a major concern in assessing the safety of underground repositories. The present model is capable of reproducing the three characteristic stages of creep behavior (i.e., primary, secondary, and tertiary creep) commonly observed in the laboratory creep tests. The sub-critical microcrack growth parameters (i.e., n and A) can be determined for Inada granite by fitting the numerical results of elapse time to failure versus the creep stress ratio curve with the experimental data under both dry and wet conditions. It is found that moisture has a significant influence on the parameter A rather than the parameter n. Use of the extended model makes it possible to analyze not only the extension of microcrack length, but also the development of EDZ around an opening as a function of time. The damaged zones mainly develop in the sidewalls of the opening in the case that the vertical stress σ₂₂ is larger than the horizontal stress σ₁₁.     

Percolation model for dilatancy-induced permeability of the excavation damaged zone in rock salt

A new percolation model is presented that predicts the dilatancy-induced permeability increase in the excavation damaged zone (EDZ) of rocks salt. The micro-fracture geometry and network properties of the rock salt samples are determined by visualisation and evaluated by using statistical and stereological methods. The permeability at full connectivity is modelled using the cubic law with a semi-empirical estimation of the micro-fracture aperture. This model is coupled with a percolation model to incorporate the connectivity behaviour. The percolation threshold is related to the dilatancy boundary, which is defined as the starting point for the energy release that causes the grain boundaries to dislocate. The shift between the dilatancy boundary and the percolation threshold is further applied to complete the modelling approach. The model is calibrated and validated by the stress-permeability results of the triaxial measurements. The matches vary from satisfactory to excellent.     

On the thermal impact on the excavation damaged zone around deep radioactive waste disposal

Clays and claystones are considered in some countries (including Belgium, France and Switzerland) as a potential host rock for high activity long lived radioactive waste disposal at great depth. One of the aspects to deal with when assessing the performance of the disposal is related to the effects of the temperature elevation due to the placement of exothermic wastes on the host rock. The potential effects of the thermal impact on the excavation damaged zone (EDZ) in the near field are another important issue that was the goal of the TIMODAZ European research project. In this paper, some principles of waste disposal in clayey host rocks at great depth are first presented and a series of experimental investigations carried out on specific equipment specially developed to face the problem are presented. Both drained and undrained tests have been carried out to investigate the drained thermal volume changes of clays and claystone and the thermal pressurization occurring around the galleries. The importance of proper initial saturation (under in situ stresses) and of satisfactory drainage conditions (in spite of the significantly low permeability of claystones) is emphasized, leading to the development of a new hollow cylinder apparatus. It is observed that claystones cannot be considered as overconsolidated clays given that they can exhibit, as the Callovo-Oxfordian claystone does, a thermoplastic contraction. Mechanical and thermal hardenings are however observed, extending the knowledge already gained on clays to claystones. A new method of determining the thermal pressurization coefficient in the laboratory is described and the data obtained allow completing existing data in the field. Finally, the hollow cylinder apparatus makes it possible to demonstrate that the good self-sealing properties of clays and claystones can be extended to temperature effects, an important conclusion in terms of performance assessment.     

隧道工程浅埋暗挖法的施工技术

对隧道工程浅埋暗挖法进行了介绍,探讨了浅埋暗挖法施工技术的特点、开挖方法及支护方式,分析了浅埋暗挖法工程的监控量测,提出了量测管理基准,以保证隧道工程浅埋暗挖法的顺利进行。     

浅埋暗挖法隧道穿越房屋沉降控制应用分析

结合深圳地铁5号线百鸽笼站-布心站区间工程,介绍了采用浅埋暗挖法加固的施工图设计及施工工艺,对施工过程中房屋沉降进行了分析并提出房屋沉降控制方案,从而明显改善隧道内止水效果,成功解决了隧道地表及建筑物沉降问题。     

大断面暗挖隧道软弱围岩CRD法施工

结合新建铁路温福线周仓岭隧道的施工案例,介绍了大断面暗挖隧道穿越软弱土层的施工工艺,并从掘进、支护、围岩量测等方面阐述了采用CRD法施工的优越性,为该工法的推广应用提供了技术支撑。     

暗挖黄土隧道围岩与支护结构相互作用分析

以西安地铁三号线某区间暗挖隧道为工程依托,通过数值模拟分析与收敛监测相结合的方式,研究了隧道围岩压力随着开挖过程的变化,分析了隧道支护结构受力特性,结果表明,随着隧道的开挖,围岩应力逐渐释放,围岩的最大接触压力逐步由上向下转移,并且不是完全对称分布的。拱腰处受力往往最大,在隧道设计及施工中应予以高度重视,对支护结构进行加强设计或采取其他安全措施。     

隧道开挖支护施工现状分析及研究

介绍了隧道工程支护的类型及作用,主要对锚杆施工、钢架及大拱脚架施工、超前小导管施工、喷射混凝土施工的现状进行了分析,探讨了各项施工技术应注意的问题与要点,为同类工程的施工积累了经验。     

浅埋暗挖隧道施工引起的地表塌陷分析及控制

介绍了浅埋暗挖隧道施工造成地表塌陷的成因与过程,从截排地表水、超前支护、仰拱、衬砌、下台阶开挖等方面,阐述了控制隧道施工中地表塌陷的措施,确保了工程的安全性。     

Numerical investigation of arching mechanism to underground excavation in jointed rock mass

In this paper, the discontinuous deformation analysis (DDA) is applied to numerically investigate the formation of pressure arch and the stabilization mechanism of rock bolts for underground excavation in laminated rock mass. A global pressure arch with elevated stress is observed sustaining the weight of the overburden and providing the natural shield over the opening. Below the pressure arch is a loosened zone, where a group of local voussoir beam arches are formed to transfer the weight of each layer to the abutments. Detailed parametric studies regarding the in-situ stress ratio, joint friction angle, overburden depth and dip angle of strata are conducted and their influences on the formation of global pressure arch and local voussoir beam arches are identified and discussed. Based on the observed phenomena, the corresponding reinforcement scheme is proposed and the effectiveness and stabilization mechanism are examined.