Compensation excavation method control for large deformation disaster of mountain soft rock tunnel

In recent years,the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China.It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling.Hence,the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation.It uses supportive strategies to counteract the excavation effects successfully.This paper provides an overview of the fundamental ideas of the compensation excavation method,methodologies,and field applications.The scientific validity and feasibility of the compensation excavation method were investigated through the practical engineering study of the Muzhailing and Changning tunnels.

Numerical modeling of large deformation and nonlinear frictional contact of excavation boundary of deep soft rock tunnel

Roadways excavated in soft rocks at great depth are difficult to be maintained due to large deformation of surrounding rocks, which greatly influences the safety and efficiency of deep resources exploitation. During the excavation process of a deep soft rock tunnel, the rock wall may be compacted due to large deformation. In this paper, the technique to address this problem by a two-dimensional (2D) finite element software, large deformation engineering analyses software (LDEAS 1.0), is provided. By using the Lagrange multiplier method, the kinematic constraint of non-penetrating condition and static constraint of Coulomb friction are introduced to the governing equations in the form of incremental displacement. The numerical example demonstrates the efficiency of this technology. Deformations of a transportation tunnel in inclined soft rock strata at the depth of 1 000 m in Qishan coal mine and a tunnel excavated to three different depths are analyzed by two models, i.e. the additive decomposition model and polar decomposition model. It can be found that the deformation of the transportation tunnel is asymmetrical due to the inclination of rock strata. For extremely soft rock, large deformation can converge only for the additive decomposition model. The deformation of surrounding rocks increases with the increase in the tunnel depth for both models. At the same depth, the deformation calculated by the additive decomposition model is smaller than that by the polar decomposition model.

Stability evaluation method of large cross-section tunnel considering modification of thickness-span ratio in mechanized operation

Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.

Time-dependent squeezing deformation mechanism of tunnels in layered soft-rock stratum under high geo-stress

Large squeezing deformation of layered soft rock tunnel under high geo-stress has a significant time-dependent deformation behavior.In this paper,we studied the deformation mechanism during the construction period of deep-buried softrock tunnel by means of a combination of field observations and a numerical method.First,a new classification criterion for large deformations based on the power exponent variation law between the deformation and the strength-stress ratio is proposed.Then,the initial damage tensor reflecting the bedding plane(joint)distribution and an equivalent damage evolution equation derived from the viscoplastic strain are introduced based on the geometric research method,i.e.,a new rheological damage model(RDL model)of layered soft rock is established consisting of elastic,viscous,viscoelastic,viscoplastic and plastic elements.A field test was conducted on the Maoxian tunnel in Sichuan province,southwestern China,which is in broken phyllite(layered soft rock)under high geo-stress.The tunnel has experienced large deformation due to serious squeezing pressure,thus we adopted double primary support method to overcome the supporting structure failure problems.The rheological parameters of phyllite in the Maoxian tunnel were recognized by using SA-PSO optimization,and the RDL model does a good job in describing the time-dependent deformation behavior of a layered soft-rock tunnel under high geo-stress.Thus,the RDL model was used to investigate the supporting effect and bearing mechanism of the double primary support method.Compared with the single primary support method,the surrounding rock pressure,secondary lining force,surrounding rock deformation,and the depth of the damage to the rock mass was reduced by 40%-60%after the double primary support method was used.

Analysis of mechanical behavior of soft rocks and stability control in deep tunnels

Due to the weakness in mechanical properties of chlorite schist and the high in situ stress in Jinping II hydropower station, the rock mass surrounding the diversion tunnels located in chlorite schist was observed with extremely large deformations. This may significantly increase the risk of tunnel instability during excavation. In order to assess the stability of the diversion tunnels laboratory tests were carried out in association with the petrophysical properties, mechanical behaviors and waterlweakening properties of chlorite schist. The continuous deformation of surrounding rock mass, the destruction of the support structure and a large-scale collapse induced by the weak chlorite schist and high in situ stress were analyzed. The distributions of compressive deformation in the excavation zone with large deformations were also studied. In this regard, two reinforcement schemes for the excavation of diversion tunnel bottom section were proposed accordingly. This study could offer theoretical basis for deed tunnel construction in similar geological condition~

极高地应力软岩隧道非对称变形机理及支护优化研究

针对极大断面公路隧道施工中出现的非对称大变形问题,考虑高地应力第一主应力与隧道轴线关系、层状软岩夹层与互层状态、掌子面软岩空间不对称、地下水等因素,基于对工程地质条件、围岩与支护结构失效及破坏特征的分析,结合岩样物理力学特性室内试验研究及地应力实测情况,探究了非对称大变形形成机理并提出针对性的支护结果优化方案。结果表明:高地应力层状软岩隧道围岩不对称变形是在岩层倾角α、最大水平主应力与隧道轴线夹角β和岩层夹角γ、围岩岩性和地下水综合作用下的大变形,围岩不对称部位由以上几种因素共同决定;当主应力σ1与隧道轴线既不垂直也不平行时,会产生挤压性偏压构造水平地应力,使隧道横断面侧向受力不对称,发生偏压性非对称大变形;通过改变锚杆的布设方式、提高超前注浆小导管的长度和刚度、喷射临时封闭、在防水板与喷射砼间增加高密度橡塑海绵板缓冲层等措施,可以有效的减少变形量,防止围岩因开挖扰动而松动和坍塌。

施工期铁路隧道软岩大变形快速分级方法研究

研究目的:西南复杂艰险山区等典型构造活跃区的构造地质环境复杂,断裂、褶皱发育,构造应力显著,铁路隧道围岩大变形问题突出,随着构造活跃区铁路隧道工程日益增加,将面临更严峻的大变形问题。在隧道施工开挖过程中,快速判别可能发生的大变形等级,有利于施工工法的调整和支护措施的制定。研究结论:(1)深入分析构造软岩大变形工程案例,以施工期掌子面开挖揭示围岩分级数据为基准,结合区域地应力、岩层厚度、岩性等大变形关键控制因素,快速判定大变形等级,提出了施工期铁路隧道围岩大变形快速分级方法,并结合典型工程案例对分级方法的有效性和准确性进行了验证;(2)本研究成果可应用于施工期间铁路隧道开挖围岩大变形的快速分级,适用于工程地质勘察领域。

考虑湿度应力的深部软岩隧道大变形控制研究

为探明深部高地应力软岩隧道大变形产生机理,制定适应大变形控制措施,以月直山隧道为工程依托,首先明确求解围岩形变压力与松动压力的Kastner与Caquot公式,基于岩体弹塑性力学与连续介质理论建立围岩湿度应力解析解,采用收敛-约束法绘制出3种围岩应力作用下围岩与初期支护特征曲线,分析断面变形过程中围岩与支护结构相互作用规律及3种应力占比演化规律。分别以混凝土与型钢钢架作为二衬支护结构对月直山隧道围岩稳定性进行计算分析,明确考虑湿度应力与松动压力条件下隧道二衬最优支护时机与支护参数,以支护结构安全系数FS评判出最优支护方案并对隧道软岩大变形进行治理。结果表明:当围岩径向位移达到550 mm时,仅考虑形变压力Pi时围岩对支护结构的压力P仅为0.813 MPa,考虑湿度应力Pw与松动压力Pa时P增大为1.372 MPa,湿度应力与松动应力总占比达40.7%,仅考虑形变压力而设计的支护结构不满足围岩稳定性要求;根据“卸压支护”理念,确定以“位移释放峰值upeak=0.325 m”与“间距d=0.7 m”作为增设第二层钢架的最佳支护时机与支护参数,现场二次钢架设置24天后使围岩变形收敛于50.8 mm,围岩大变形得到控制,研究成果可为今后相关隧道工程设计与施工提供参考。

NPR锚索对跨断层软岩大变形隧道控制技术研究

为探究NPR锚索对东马场跨断层软岩大变形隧道控制效果,首先对NPR锚索进行静力拉伸试验,验证其恒阻大变形的能力和具有良好的抵御外力的效果;随后开展NPR锚索对东马场隧道围岩变形控制的三维物理模型试验。试验现象和数据表明:在开挖过程中,隧道围岩也没有出现较大垮落和坍塌,NPR锚索对软岩隧道围岩有较好的支护效果。在加载完成后,NPR锚索对非断层处的隧道围岩最大位移约为14 mm,断层处的围岩最大位移约为21 mm,隧道区域所受应力分布的不规律性,导致隧道围岩出现挤压变形,位移曲线呈振荡状。在NPR锚索的支护下,围岩应力最大发生在左拱肩,围岩临空面3 cm处切应力最大(0.3 MPa),隧道未出现大规模的不对称破坏现象,隧道总体呈现出“小塌而不垮”,变形总体可控。

西(宁)成(都)铁路高地应力节理发育软岩地层隧道支护体系研究

为保证西成铁路高地应力节理发育软岩大变形隧道安全修建,采用现场勘察、室内试验、地应力测试、工程类比、数值模拟等方法展开研究,结果表明,西成铁路与毗邻兰渝线地质条件类似,均以二叠系、三叠系板岩与砂岩为主,层理清晰、节理裂隙发育,地应力以水平主应力为主导,水平主应力在10~30 MPa之间,竖直主应力在4~13 MPa之间,有较强水平构造应力作用,兰渝线控制围岩变形主要采用增加预留变形量、自进式长锚杆、钢花管加固、增加初支及衬砌刚度、钢纤维喷射混凝土等技术措施。在此基础上针对西成铁路节理发育软岩大变形主要发生在垂直节理倾角方向上的特点,提出首先增大矢跨比,然后增大钢拱架刚度,对于Ⅲ级大变形在垂直节理方向设置预应力锚索的非对称大变形隧道支护体系,该支护体系相比传统支护体系能够减小13.8%~21.2%软岩变形,对于控制节理发育软岩变形效果良好。

香炉山隧洞不良地质段“L”型地面超前注浆方案研究

为解决隧道(洞)建设过程中不良地质段突泥涌水和软岩大变形等问题,依托滇中引水工程香炉山隧洞,提出一种采用全孔长度超过500 m的地面“L”型定向钻孔注浆并辅以洞内超前注浆的加固方法,在实际工程中确定这一方法的具体设计方案。首先,通过现场地质调查与分析,揭示不良地质区段香炉山隧洞建设的技术难点;其次,介绍“L”型定向钻孔注浆的施工过程及注浆工艺;然后,设计出一种能够提高地层稳定性的“L”型地面超前注浆方案,并对地层进行加固;最后,采用掌子面揭示、注浆技术以及大地电磁检测等手段证明现场注浆效果。研究结果表明:1)“Z1+Z2+Z4”钻场设计为最优地面超前注浆技术方案;2)“L”型定向钻孔注浆辅以洞内超前注浆技术可满足盲区注浆区域覆盖问题,实现真正意义上的超前治理。

高地应力软岩地层敞开式TBM法隧洞围岩变形控制技术——以香炉山隧洞为例

为解决敞开式TBM在滇西地区高地应力软岩地层施工中遭遇围岩大变形而导致的支护破坏、设备频繁被卡、隧洞侵限等工程难题,通过分析围岩允许变形量与变形规律,提出围岩控制时空原则:有效初期支护施作时间为开挖后15 d内、空间位置为距掌子面30 m范围内,TBM掘进日进尺不低于2 m/d。通过不同类型的支护结构现场试验,得出控制围岩变形的有效措施为预应力长锚索主动控制变形、灌混凝土箱体H型钢拱架被动强支撑。另通过滇中引水香炉山隧洞敞开式TBM施工实践,开发出“掌子面位置刀盘扩挖预留允许变形量、围岩出护盾灌混凝土箱体拱架被动强支撑、隧洞上半圆前置式自动化喷混凝土早封闭、预应力长锚索主动控制深层围岩变形、隧洞底部自进式锚杆后补强”等围岩变形有效控制技术。

基于变形控制的某深埋软岩水工隧洞初期支护参数的选择与验证

大变形下围岩的稳定控制一直是水利水电、公路、铁路等行业的传统难题,尚未形成一套验证软岩大变形等级下初期支护型式及参数选取的经验方法。依据某深埋水工隧洞工程地质情况,选择典型洞段预测挤压变形风险,利用控制变形估算所需支护力,依据规范和相关工程经验确定支护类型与参数的同时,考虑实际开挖过程利用数值仿真分析验算支护的合理性。结果表明,该隧洞具有极大的大变形风险,采用支护力的方法所确定的支护类型和参数基本合理,可将围岩变形有效控制在规范要求的1.0%~3.0%范围,且锚杆长度及支护应力等均未超过极限强度。

高应力软岩隧洞稳定性及支护模拟研究

为分析高应力软岩隧洞的变形特征和支护效应,采用FLAC3D软件模拟滇中引水工程深埋输水隧洞软弱围岩稳定性与支护措施,对毛洞和支护条件下围岩的位移场、应力场和损伤破坏区的分布规律以及衬砌受力状态进行分析和围岩稳定性评价。结果表明:对深部软岩施加锚喷支护可以提高岩体的围压和承载能力,显著减小软弱围岩的变形和损伤破坏程度,但仅依靠锚喷支护时,围岩变形仍然较大。施加永久衬砌时的围岩位移释放率越大,衬砌的内力越小,但围岩的变形量越大。建议对高应力软岩洞室采用全断面锚喷支护,提高初期支护的刚度和强度。可根据不同围岩位移释放率条件下永久衬砌的内力和隧洞的变形特征,结合永久衬砌的承载能力和隧洞的净空要求,确定合适的永久衬砌支护时机。

大断面软弱围岩隧道施工方法研究

为了解决大断面软弱围岩隧道的施工技术难题,以G30连霍高速公路某隧道工程实例为依托,通过现场隧道拱顶下沉、周边收敛及支护结构受力的监控量测情况,开展大断面软弱围岩隧道合理施工方法的研究。结果表明:微台阶环形开挖预留核心土法能够保证隧道施工安全、质量、进度要求,满足项目建设需要。

隧道软岩大变形处治施工技术应用

研究了隧道软岩大变形处治施工技术应用,在掌握大变形形成机理的基础上,从开挖施工工法、大变形处治原则、锚杆施工技术、超前注浆小导管施工技术等方面出发,分析了隧道软岩大变形处治施工技术应用要点,明确软岩大变形的主要影响因素,采用科学理论开展模拟分析,提高技术细节控制效果。

Lateral damage mechanism of the double-track tunnel in the mountainous layered soft rock and NPR anchor cable control

Due to complex geological formations,lateral damage often occurs during excavation in mountainous layered soft rock double-track tunnels.This paper discusses the stresses and the damage characteristics of the surrounding rock under overload in a mountainous layered soft rock double-track tunnel through indoor model experiments to provide a basis for the effective control of lateral damage.The experiments show that the conventional support method cannot effectively control the lateral damage due to interlayer sliding.Therefore,the negative Poisson’s ratio(NPR)anchor/cable control method is proposed.And the scientificity and feasibility of the NPR anchor/cable control technology are proved by the field application and monitoring data of the Minxian Tunnel and Changning Tunnel.It is further demonstrated that high preload is the most effective way to control the lateral damage in layered soft rock tunnels.

川西地区极破碎软岩隧道大变形机制分析及控制技术——以查针梁子隧道工程为例

为解决隧道建设过程中初期支护变形侵限严重、频繁塌方等问题,依托G0615久治至马尔康高速公路查针梁子隧道进行研究,通过微台阶开挖、增大预留变形量、双层钢架支护、加强锁脚、机械化施工快速封闭成环、加强施工管理等工程措施,有效控制了围岩大变形。研究结果表明:1)通过针对性的加强支护参数,能够控制初期支护变形,有效开挖,初期支护侵限率由最初的29%下降为0。2)通过缩小台阶长度,采用微台阶,单工序,减小了初期支护封闭成环时间,封闭成环时间由40~50 d减小到15~20 d。3)由于空间有限,适时引进部分机械设备,采用了立架台车,可有效减少立架时间,加快施工进度,单掌子面月(最低)掘进进尺由6 m/月提高到36 m/月。

挤压型软岩隧道大变形机理与支护参数优化研究

地应力水平是隧道挤压型软岩大变形主导因素之一,深部地应力与岩体力学特性对隧道设计具有较强参考价值。以西成铁路甘青隧道地应力测试与岩体力学试验为基础,深入分析测试数据,采用数值模拟方法进行不同地应力水平的计算,对比现场实测数据,结果发现,测区地应力以水平地应力为主导,三向地应力关系为S_(H)>S_(h)>S_(V),具有较强的水平构造作用,地应力比值在1.5~4.5之间,随着埋深增加逐渐减小;岩体荷载-变形(P-W)曲线外包络线形态大体上呈现为“下凹形”,以塑性变形为主;仅有少量弹性变形,岩体抗剪断应力-应变(τ-ε)曲线基本呈抛物线形,屈服值不明显,以塑性破坏为主。随着地应力比值增加,隧道水平变形越来越大,竖直变形先减小后增加,二者比值介于0.70~2.45之间,均小于地应力比值,最大变形由拱顶向拱腰转移,围岩主应力差值逐渐增加,挤压形变压力越来越大。在此基础上,针对甘青隧道进口的水平挤压大变形特征,提出增大拱架刚度、加强锁脚、加强拱架纵向连接、增大隧道预留变形量等支护优化措施,现场实测表明,这些措施有效控制了隧道变形。

基于卸荷路径的软岩大变形隧道计算模型

近些年来,软岩大变形隧道施工带来的安全事故日益频繁,其主要原因是目前暂未形成有针对性的、可以准确反映软岩大变形力学行为的隧道计算模型。隧道开挖过程实际是一个卸荷的过程,在这种应力路径条件下,隧道塑性区内围岩的力学性能相对未开挖状态减弱。本文基于隧道典型软岩—泥岩卸荷三轴试验得到考虑峰后损伤的力学本构模型,并建立软岩隧道计算模型。与传统Fenner公式计算结果进行对比发现,本文模型更加符合高地应力下软岩隧道开挖和支护计算结果。利用Euler显式差分求解算法对模型进行理论求解,研究不同支护力、不同黏聚力、不同摩擦角、不同变形模量对隧道塑性圈半径与洞周位移的影响。基于FISH语言平台,将计算模型嵌入FLAC 3D得到了支护时间对支护效果的影响。最后基于龙溪隧道的现场实测数据验证了本文的隧道计算模型。研究成果可以为准确计算大变形段落围岩响应提供理论依据。