Inverting the rock mass P-wave velocity field ahead of deep buried tunnel face while borehole drilling

Imaging the wave velocity field surrounding a borehole while drilling is a promising and urgently needed approach for extending the exploration range of the borehole point.This paper develops a drilling process detection(DPD)system consisting of a multifunctional sensor and a pilot geophone installed at the top of the drilling rod,geophones at the tunnel face,a laser rangefinder,and an onsite computer.A weighted adjoint-state first arrival travel time tomography method is used to invert the P-wave velocity field of rock mass while borehole drilling.A field experiment in the ongoing construction of a deep buried tunnel in southwestern China demonstrated the DPD system and the tomography method.Time-frequency analysis of typical borehole drilling detection data shows that the impact drilling source is a pulse-like seismic exploration wavelet.A velocity field of the rock mass in a triangular area defined by the borehole trajectory and geophone receiving line can be obtained.Both the borehole core and optical image validate the inverted P-wave velocity field.A numerical simulation of a checkerboard benchmark model is used to test the tomography method.The rapid convergence of the misfits and consistent agreement between the inverted and observed travel times validate the P-wave velocity imaging.

Support pressure assessment for deep buried railway tunnels using BQ-index

Estimation of support pressure is extremely important to the support system design and the construction safety of tunnels.At present,there are many methods for the estimation of support pressure based on different rock mass classification systems,such as Q system,GSI system and RMR system.However,various rock mass classification systems are based on different tunnel geologic conditions in various regions.Therefore,each rock mass classification system has a certain regionality.In China,the BQ-Inex(BQ system)has been widely used in the field of rock engineering ever since its development.Unfortunately,there is still no estimation method of support pressure with BQ-index as parameters.Based on the field test data from 54 tunnels in China,a new empirical method considering BQ-Inex,tunnel span and rock weight is proposed to estimate the support pressure using multiple nonlinear regression analysis methods.And then the significance and necessity of support pressure estimation method for the safety of tunnel construction in China is explained through the comparison and analysis with the existing internationally widely used support pressure estimation methods of RMR system,Q system and GSI system.Finally,the empirical method of estimating the support pressure based on BQ-index was applied to designing the support system in the China’s high-speed railway tunnel—Zhengwan high-speed railway and the rationality of this method has been verified through the data of field test.

Comparison between the Seismic Performance of Buried Pipes and Pipes in a Utility Tunnel

A utility tunnel system consists of pipes and ancillary facilities.In this paper,a finite element model of a concrete utility tunnel with pipes inside is established.Several tunnel segments were built to simulate a real utility tunnel,while the pipe was fixed by springs on the brackets in the utility tunnel.Using the discrete soil spring element to simulate the soil-structure interaction,actual earthquake records were adopted as excitation to analyze the seismic responses of pipes in a utility tunnel.Moreover,the influences of different parameters,including soil type,earthquake records,and field apparent wave velocity on the seismic responses of the utility tunnel and the pipes inside were studied.Finally,the seismic responses of buried pipes were analyzed and compared with those of pipes in a utility tunnel to evaluate the seismic performance of pipes for two working conditions.

Mechanical response features and failure process of soft surrounding rock around deeply buried three-centered arch tunnel

Due to the extreme complexity of mechanical response of soft surrounding rock(SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties(PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model(PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load(HL) was in the range of 130 k N to 170 k N, the vertical load(VL) was in the range of 119 k N to 153.8 k N), rapid crack coalescence(the HL was in the range of 170 k N to 210 k N, the VL was in the range of 153.8 k N to 182.5 k N) and residual strength(the HL was greater than 210 k N, the VL was greater than 182.5 k N). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC3 D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the relationship of deformation localization and progressive failure of SR around a tunnel under high stress conditions was discussed.

Geostress Measurement for Deep-Buried Long Tunnel through Niba Mountain

In the geostress measurement for Niba Mountain on Ya＇an-Lugu Expressway, results of Kaiser effect tests combined with focal mechanism solution were compared with those obtained by hydraulic fracturing method, both of which are basically coincident. It is shown that the principal stress increases with burial depth ; the maximum principal stress is about 45 MPa, which is larger near fault zones because of stress concentration, and its direction ranges from N20°W to N75°W.

Analysis of mechanical behaviors of big pipe roof for shallow buried large-span tunnel

A series of researches on mechanical behaviors of big pipe roof for shallow large-span loess tunnel were carried out based on the Wenxiang tunnel in Zhengzhou—Xi'an Special Passenger Railway. The longitudinal deformations of the pipe roofs were monitored and the mechanical behaviors of the pipe roofs were analyzed at the test section. A new double-parameter elastic foundation beam model for pipe roof in shallow tunnels was put forward in Wenxiang tunnel. The measured values and the calculation results agreed well with each other,revealing the force-deformation law of big pipe roof in loess tunnel:At about 15 m in front of the excavating face,the pipe roof starts to bear the load;at about 15 m behind the excavating face,the force of the pipe roof tends to be stabilized;the longitudinal deformation of the whole pipe roofs is groove-shaped distribution,and the largest force of pipe roofs is at the excavating face. Simultaneously,the results also indicate that mechanical behaviors of pipe roof closely relate to the location of the excavation face,the footage of the tunnelling cycle and the mechanics parameters of pipe roof and rock. The conclusions can be reference for the design parameter optimization and the construction scheme selection of pipe roofs,and have been verified by the result of numerical analysis software FLAC3Dand deformation monitoring.

Study on calculation of rock pressure for ultra-shallow tunnel in poor surrounding rock and its tunneling procedure

A computational method of rock pressure applied to an ultra-shallow tunnel is presented by key block theory, and its mathematical formula is proposed according to a mechanical tunnel model with super-shallow depth. Theoretical analysis shows that the tunnel is subject to asymmetric rock pressure due to oblique topography. The rock pressure applied to the tunnel crown and sidewall is closely related to the surrounding rock bulk density, tunnel size, depth and angle of oblique ground slope. The rock pressure applied to the tunnel crown is much greater than that to the sidewalls, and the load applied to the left side-wall is also greater than that to the right sidewall. Mean-while, the safety of the lining for an ultra-shallow tunnel in strata with inclined surface is affected by rock pressure and tunnel support parameters. Steel pipe grouting from ground surface is used to consolidate the unfavorable surrounding rock before tunnel excavation, and the reinforcing scope is proposed according to the analysis of the asymmetric load induced by tunnel excavation in weak rock with inclined ground surface. The tunneling procedure of bench cut method with pipe roof protection is still discussed and carried out in this paper according to the special geological condition. The method and tunneling procedure have been successfully utilized to design and drive a real expressway tunnel. The practice in building the super-shallow tunnel＆amp;nbsp;has proved the feasibility of the calculation method and tunneling procedure presented in this paper.

深埋岩溶隧道爆破开挖对围岩损伤及渗流特性的影响

深埋岩溶隧道开挖会造成围岩特殊的损伤破坏形式,并且损伤区也会影响围岩渗流场及隧道边界的涌水状况,对深埋岩溶隧道爆破开挖作用下围岩的损伤及渗流特性有重要的研究意义。为了研究爆破开挖对深埋岩溶隧道围岩损伤及渗流的影响规律,基于COMSOL Multiphysics软件建立数值模型并嵌入应力-渗流-损伤耦合方程式进行计算,采用解析法计算了简化条件下岩溶隧道开挖时围岩的应力分布,并与数值计算结果进行比较。结果表明:解析法与数值法计算的围岩应力分布有一致性,爆炸荷载使靠近溶洞侧隧道肩部及脚部区域会产生较大的拉应力;爆破后会在隔水岩柱形成“齿”状损伤区,同时引起肩部及脚部区域流速的增加,其可作为判断溶洞方位的参考依据;溶洞净距减小、洞径及水压增加会引起“齿”延伸倾角及最大涌水位置变化、隧道边界涌水量的增加,可根据“齿”延伸方向判断损伤区检测的合理方位,根据最大涌水位置变化、隧道边界涌水量的变化,合理调整涌水防治措施强度及重点防治部位。研究成果可为溶洞位置判定、隧道损伤区检测以及边界涌水防治措施提供参考。

浅埋暗挖交叉相贯隧道施工力学行为试验研究

为完善浅埋暗挖交叉相贯隧道在施工过程中的受力形式及变形特征,依托青岛某地铁工程,根据所选地铁车站的地质条件及衬砌结构特点浇筑衬砌模型并配制围岩相似材料,利用模型试验对采用全断面法在Ⅴ级围岩环境下进行的风道和车站主体开挖过程的力学行为展开研究,并从隧道衬砌结构变形及地层内部位移变化规律两方面分析了浅埋暗挖交叉相贯隧道全断面开挖施工的力学行为。结果表明:对于交叉相贯位置处的隧道结构,已有隧道结构将改变后续施工隧道衬砌结构应变最大值及其出现位置;位于交叉相贯隧道结构附近不同象限内的围岩分别处于水平变形累加区和往复区;地表竖向变形最大点位于后续施工的车站上方且与交叉相贯位置存在一定距离,而在交叉相贯位置处的地表竖向变形值稍小;模型试验明确了交叉相贯隧道在施工过程中围岩及衬砌结构的变形特征,给出了隧道结构地表最大变形与施工步序间的时空关系;研究结果可为相关交叉相贯隧道结构的施工及设计提供依据。

黄土盾构隧道开挖围岩扰动特性模型试验研究

为了探究不同含水率和埋深等工况下的黄土盾构隧道开挖对围岩的扰动作用特征,采用相似模型试验,首先通过三轴试验测定了不同含水率下原状黄土物理参数及强度指标,通过大量试配得到了不同含水率下与原状黄土强度指标参数相似的试验用土。其后,考虑盾构隧道盾尾间隙特征,开展不同含水率及埋深等组合工况下盾构开挖模拟试验,通过微型土压力传感器、百分表等监测元件以及数字图像技术等手段,分析了不同工况下地层变形、地表沉降和围岩应力的变化规律。研究发现:含水率较低时,围岩的自稳能力强;含水率越高,埋深越大,开挖对地层的扰动作用也越大;地表最大沉降值与含水率呈正相关,与埋深呈负相关;围岩剩余应力随含水率和埋深的增大而增大,但当含水率增大至一定值(26.6%)时,围岩剩余应力骤减;基于不同含水率下的围岩应力及变形发展规律,可将黄土含水率分为自稳、形变以及松动含水率,基于含水率和埋深引起的围岩松动情况,可将不同工况下的黄土盾构隧道围岩压力作用模式按照形变压力和松动压力计算,以更加适应黄土地层的特性。

降雨入渗对防军隧道浅埋小净距段围岩稳定性的影响

为控制降雨入渗对浅埋小净距隧道围岩稳定性的影响,以义东高速公路防军隧道为依托,基于流固耦合理论和水土特征曲线,采用MIDAS GTS NX有限元软件建立浅埋小净距隧道数值模型,对雨季施工时的土体孔隙水压力、围岩变形特征和边仰坡安全系数展开分析。结果表明:随着降雨入渗的持续,围岩及边仰坡土体基质吸力逐渐减小,其土体抗剪强度也随之降低,稳定性变差。经过7 d累积降雨,孔隙水压力增大趋势逐渐放缓,围岩变形达到最大值,工况1的拱顶沉降增大了21.48%,且边仰坡安全系数小于1,处于失稳状态。洞口段采取加固和排水措施来控制围岩的稳定性,边仰坡的安全系数较加固前提升了17.27%,取得了良好的效果,保证了隧道后期的安全施工。

城市浅埋隧道自然排烟竖井临界间距研究

竖井间距会改变竖井内外压差,当竖井内外压差为0时,隧道火灾烟气将无法排出,此时竖井对应位置为竖井临界间距。由竖井内外口压差理论分析,给出竖井临界间距理论模型,再采用FDS模拟进行仿真验证。结果表明:设置竖井可明显降低隧道温度,竖井间距为临界间距时,温度下降幅度接近150℃,人员疏散路径温度低于60℃,竖井排烟效率在55%~80%,可有效进行竖井排烟;当竖井间距大于竖井临界间距时,隧道内烟气压强小于竖井出口处风压,竖井排烟效率低于50%。

基于BIM技术的浅埋隧道无限元法数值研究

近年来,BIM技术在交通运输基础工程领域的应用日益广泛,如地铁、高铁、公路、隧道等项目全生命周期的管理都有BIM技术的参与。本研究通过BIM软件–Revit建立浅埋隧道的信息模型,基于BIM信息模型,导入ABAQUS有限元分析软件,对越秀公园站浅埋暗挖多孔隧道进行有限元与无限元耦合模拟,验证了无限元在隧道数值模拟中的可行性。其次通过设置不同的工况,验证了无限元与有限元耦合模拟的准确性,并且研究了隧道的开挖对不同工况下,地表沉降和衬砌内力的影响,得出最优的开挖工序,为后续浅埋隧道的力学行为的研究提供借鉴。

非线性破坏准则下浅埋隧道的稳定性分析

隧道围岩压力值是浅埋隧道设计计算的重要参数。为进一步提高围岩压力计算结果的可靠性,以传统浅埋隧道坍塌模型为基础,提出了圆弧滑移面破坏模式,同时基于非线性Mohr-Coulomb破坏准则,运用极限分析上限法推导了地震力作用下浅埋隧道围岩压力的计算公式,验证了计算结果的可靠性,并对影响因素进行了探讨。与实际工程和已有成果的对比分析证明了理论公式具有较高的可靠性和准确度。研究还发现:围岩压力受非线性系数和初始粘聚力的影响较为显著,非线性系数越大、初始粘聚力越小,围岩压力越大;随着待定参数K(水平围岩压力与竖向围岩压力的比值)的减小,水平围岩压力减小,竖向围岩压力增大;地震力对围岩压力的影响不容忽视,竖向地震力单独作用对围岩压力的影响最大,水平和竖向地震力共同作用的影响次之,而仅有水平地震力作用的影响最小。随着水平与竖向地震力系数的增大,围岩压力也在增大。分析结果对于大部分的隧道,尤其是易受地震影响的浅埋隧道研究具有较高的参考价值。

广义章-朱准则在深埋隧道数值分析中的适用性研究

深部岩体隧道的智能建造是当今隧道工程建设的重要发展趋势。为准确模拟深部岩体的三维应力状态,提高深埋隧道数值计算精度,将广义章-朱岩体强度准则引入深埋隧道数值分析中,采用理论分析和数值计算相结合的方法从岩体强度准则的特性、参数以及工程应用3个角度对广义章-朱准则在深埋隧道数值分析中的适用性展开研究。结果表明:1)从准则特性的角度,广义章-朱准则能反映深部岩体的非线性特征以及中间主应力效应,适用于深埋隧道数值分析;2)从参数选取角度,提出了一种广义章-朱准则参数估算方法,有利于提高广义章-朱准则的适用性;3)工程案例表明广义章-朱准则具有较高的计算精度,在深埋条件下采用广义Hoek-Brown准则计算得到的围岩变形误差达到23%~30%,建议采用广义章-朱准则进行深埋隧道数值分析。

浅埋河谷段TBM施工应用与适宜性评价

TBM施工技术应用于隧洞开挖,技术上已经成熟,并广泛应用于深埋长大隧洞施工中。影响隧洞TBM施工的因素基本清楚,一般认为穿越浅埋河谷段隧洞采用TBM施工容易发生围岩塌方、涌水事故,不适宜采用TBM施工。为了研究浅埋河谷段TBM施工适宜性,通过两个典型的穿越浅埋河谷段隧洞TBM施工的工程实例,对比详细的工程地质条件,分析塌方的原因,进行TBM施工适宜性分析,结果表明,隧洞上覆弱风化岩体大于1倍洞径段进行适当的工程处理后,采用TBM施工是适宜性的。

浅埋隧道双侧壁导坑法施工数值模拟研究

为准确评价浅埋隧道施工过程的围岩稳定性,利用ANSYS有限元数值分析软件,对沈阳地铁10号线区间浅埋隧道双侧壁导坑法施工进行数值模拟,研究了浅埋隧道施工过程的力学特性及变形规律。结果表明:开挖中上导洞后,围岩位移、应力和支护结构内力显著增大,占整个导洞开挖的50%,且最大位移、应力和支护结构弯矩集中在拱顶、初期支护连接的薄弱处;地表沉降量随时间变化增长趋缓,开挖90 d后趋于稳定,且离开挖面越近,沉降量越大,最大沉降点出现在最先开挖的中上导洞位置;隧道开挖10 d内拱顶下沉较快,随开挖掌子面远离监测点,拱顶沉降速率逐渐减小,开挖顺序对拱顶沉降影响较大,往往先开挖的位置拱顶沉降最大。现场监测结果表明:数值计算与现场监测结果比较吻合,验证了数值分析的合理性。研究成果对浅埋隧道的安全、经济施工具有借鉴意义。

基于BIM技术的浅埋双孔隧道地震响应规律研究

通过BIM软件Revit建立浅埋双孔隧道的信息模型,基于BIM信息模型,导入ABAQUS结构分析软件,基于无限元-有限元方法应用于浅埋双孔隧道进行力学行为分析的可行性和准确性,分析隧道衬砌的刚度和设置减震层对浅埋双孔隧道在典型地震波作用下的响应规律,找到适合该浅埋双孔隧道的减震层材料和厚度,为后续浅埋隧道地震响应规律的研究提供借鉴。

深埋四孔小净距隧道围岩压力的计算方法

随着工程建设的不断发展,隧道开挖孔洞数量增多的同时,多孔洞隧道相应围岩压力计算理论并不完善.针对四孔小净距隧道,以普氏理论为基础,参考已有研究中的荷载计算模型,结合四孔隧道位置特征,将深埋四孔小净距隧道计算荷载简化,综合考虑隧道开挖顺序与中岩柱所发挥作用,提出深埋条件下的围岩压力计算方法,利用该方法,结合余姚市某四孔公路隧道进行计算,并分析隧道间净距、隧道开挖跨度与中岩柱承载能力对围岩压力的影响规律.结果表明:隧道净距会影响隧道围岩压力附加承载拱的形成,净距越大各隧道偏压程度越弱,且两中洞间净距的变化对隧道整体围岩压力的影响较大;当隧道间净距不变时,增大隧道开挖跨度,隧道洞室所承载围岩压力逐渐增大,且内侧竖向围岩压力变化均强于外侧;围岩承载能力越强,相同中土柱厚度条件下隧道开挖相互影响越小,其分担来自隧道上方附加平衡拱内松散围岩压力的效果越好,隧道支护结构所承受围岩压力越小;四孔小净距隧道中洞间距的变化对隧道整体围岩压力的影响较大,隧道偏压特性随间距的增大而逐渐减小.

渗透各向异性地层中隧洞稳态渗流场的半解析预测模型

隧洞施工和服役过程中容易出现支护结构渗流破坏、涌水等与渗流场相关的工程问题.为更方便快捷地对隧洞的孔隙压力、涌水量等进行预测并为数值模型提供验证,本文对渗透各向异性饱和地层中圆形隧洞的渗流场开展理论研究,并充分考虑注浆区/衬砌对渗流场的影响.利用坐标变换和保角映射对渗流场基本控制方程进行处理,求解围岩和注浆区/衬砌区孔隙压力分布.使用配点法处理两区域交界面各点孔压和流量协调,获得了在精确满足边界和协调条件下围岩和衬砌/注浆区渗流场的控制方程,以及孔隙压力与比流量稳态分布的半解析模型.解析解与数值解的一致性验证了模型的正确性.利用解析模型分析了衬砌渗透系数、围岩渗透性各向异性程度、注浆区厚度等因素对隧道渗流量和衬砌外水压的影响.