Study on the influence of joint spacing on rock fragmentation under TBM cutter by linear cutting test

Joint spacing is one of the most important geological factors influencing rock fragmentation by TBM cutters and TBM performance. In order to study the influence of joint spacing, full-scale linear cutting tests have been conducted for the Beishan granite samples with different joint spacing (i.e. one intact sample, two jointed samples with joint spacing of 100 mm and 400 mm). For different joint spacing, the influence of penetration depth on rock fragmentation was also explored by varying the penetration depth with an interval of 0.5 mm. During the test process, the three directional forces acting on the TBM cutter were recorded, and the rock chips formed by each cutting pass were weighed, respectively. By analysing the cutting force, crack initiation/propagation and rock chips, the influences of joint spacing on rock fragmentation process by TBM cutter were investigated. The test results showed that the increase of penetration depth cannot improve the TBM breakage efficiency after reaching a certain value for the intact rock sample, and the normal force for intruding the intact rock is larger than that for intruding the rock jointed samples. It is also found that the sample part below the joint plane is intact, thus joint can restrain the crack propagating cross the joint plane and facilitates the chips formation on the cutting surface. For the rock sample with joint spacing of 100 mm, two rock fragmentation modes were found during the cutting process. One mode is that the cracks initiate from the crushed zone under TBM cutter, and the cracks propagate to the joint plane, consequently form large rock chips. The other one is that the cracks initiate from the joint plane and then propagate to the rock cutting surface, and the cracks initiate before the formation of the crushed zone under the cutter. For the rock sample with joint spacing of 400 mm, there are two rock fragmentation stages, i.e., the normal rock fragmentation stage and the joint-controlled rock fragmentation stage. There is a transitional process between these two stages, and also the median crack can be promoted to propagate vertically to joint plane due to the joint existence. This study can provide useful guidance for operation optimization and performance prediction for TBM operating in jointed rock masses.     

Study on rock mass boreability by TBM penetration test under different in situ stress conditions

Rock mass boreability is a comprehensive parameter reflecting the interaction between rock mass and a tunnel boring machine (TBM). Many factors including rock mass conditions, TBM specifications and operation parameters influence rock mass boreability. In situ stress, as one of the important properties of rock mass conditions, has not been studied specifically for rock mass boreability in TBM tunneling. In this study, three sets of TBM penetration tests are conducted with different in situ stress conditions in three TBM tunnels of the Jinping II Hydropower Station. The correlation between TBM operation parameters collected during the tests and the rock mass boreability index is analyzed to reveal the influence of in situ stress on rock mass boreability and TBM excavation process. The muck produced by each test step is collected and analyzed by the muck sieve test. The results show that in situ stress not only influences the rock mass boreability but also the rock fragmentation process under TBM cutters. If the in situ stress is high enough to cause the stress-induced failure at the tunnel face, it facilitates rock fragmentation by TBM cutters and the corresponding rock boreability index decreases. Otherwise, the in situ stress restrains rock fragmentation by TBM cutters and the rock mass boreablity index increases. Through comparison of the boreability index predicted by the Rock Mass Characteristics (RMC) prediction model with the boreability index calculated from the penetration test results, the influence degree of different in situ stresses for rock mass boreability is obtained.     

Predicting penetration rate of hard rock tunnel boring machine using fuzzy logic

Predicting the penetration rate of a tunnel boring machine (TBM) plays an important role in the economic and time planning of tunneling projects. In the past years, various empirical methods have been developed for the prediction of TBM penetration rates using traditional statistical analysis techniques. Soft computing techniques are now being used as an alternative statistical tool. In this study, a fuzzy logic model was developed to predict the penetration rate based on collected data from one hard rock TBM tunnel (the Queens Water Tunnel # 3, Stage 2) in New York City, USA. The model predicts the penetration rate of the TBM using rock properties such as uniaxial compressive strength, rock brittleness, distance between planes of weakness and the orientation of discontinuities in the rock mass. The results indicated that the fuzzy model can be used as a reliable predictor of TBM penetration rate for the studied tunneling project. The determination coefficient (R ²), the variance account for and the root mean square error indices of the proposed fuzzy model are 0.8930, 89.06 and 0.13, respectively.     

Development of a rock mass characteristics model for TBM penetration rate prediction

The TBM tunneling process in hard rock is actually a rock or rock mass breakage process, which determines the efficiency of tunnel boring machine (TBM). On the basis of the rock breakage process, a rock mass conceptual model that identifies the effect of rock mass properties on TBM penetration rate is proposed. During the construction of T05 and T06 tunnels of DTSS project in Singapore, a comprehensive program was performed to obtain the relevant rock mass properties and TBM performance data. A database, including rock mass properties, TBM specifications and the corresponding TBM performance, was established. Combining the rock mass conceptual model for evaluating rock mass boreability with the established database, a statistical prediction model of TBM penetration rate is set up by performing a nonlinear regression analysis. The parametric studies of the new model showed that the rock uniaxial compressive strength and the volumetric joint count have predominantly effects on the penetration rate. These results showed good agreement with the numerical simulations. The model limitations were also discussed.     

掘进机刀盘滚刀间距对北山花岗岩破岩效率的影响实验研究

掘进机(TBM)开挖隧道过程中,其刀盘上滚刀间距设计的合适与否关系着破岩效率的高低。由于岩石非均匀、非连续、各项异性的特性,使用数值模拟方法研究滚刀破岩过程存在局限性。现场掘进实验主要是针对特定的掘进机做出机械运行参数优化,无法研究不同刀间距对破岩的影响。全尺寸滚刀破岩实验可以人为调整刀间距,且实验中采用大体积岩石可以避免尺寸效应的影响,因此受到了广泛的关注。采用北京工业大学自制的机械破岩试验平台,安装17英寸(432 mm)盘形滚刀,选取尺寸为1000 mm×1000 mm×600 mm的北山完整花岗岩试样,进行了5组刀间距的线性切割试验。实验中采集滚刀三向力,分层收集岩片且对其进行称重。对不同刀间距作用下的平均法向力、平均滚动力和比能进行了分析研究。当贯入度较小时,刀间距对平均法向力和平均滚动力的影响都不明显,随着贯入度的增加,刀间距对平均法向力和平均滚动力的影响增加。对于所有的刀间距而言,增加贯入度会产生更多的岩片,但并不一定会提高破岩效率,对于北山花岗岩而言,当刀间距与贯入度的比值为30左右时,比能值最低,此时破岩效率最高。     

基于耦合FDM-DEM方法的TBM滚刀最优化研究

为确定TBM盘型滚刀的最优布置,结合有限差分法(FDM)和离散元法(DEM)的优点,采用FDM-DEM耦合的数值模拟方法,对不同刀间距和贯入度条件下TBM双滚刀破岩过程进行三维动态仿真模拟,分析研究了不同滚刀配置对岩石破碎效果的影响。为了验证所提出方法的可行性和准确性,利用线性切割机(LCM)对科罗拉多红色花岗岩进行了切割试验,通过对比分析线性切割试验数据,验证了所提出方法的可行性。数值模拟结果表明：对于科罗拉多红色花岗,滚刀法向力和切向力会随着刀间距和贯入度比值的增加先减少后增大,当刀间距和贯入度的比值为20左右,滚刀法向力和切向力最小。线性切割试验和数值模拟结果均表明,当间距和贯入度的比值在17～20左右,岩石切割的比能量最低,此时TBM切割效率最高。文章提出方法的方法可以为TBM滚刀刀头配置提供重要依据。     

长大煤矿斜井TBM刀具磨损影响因素与规律研究

TBM刀具的磨损是影响TBM施工效率的重要因素。以TBM掘进中的围岩磨蚀性、围岩强度、刀盘转矩和刀盘转速为研究对象,研究了长大煤矿斜井施工过程中TBM刀具磨损的影响因素和规律。依托国内首条TBM施工的神华神东补连塔煤矿斜井工程,通过对掘进过程中现场数据的实时监测,获取了刀具单周磨损量、围岩磨蚀性、围岩强度、刀盘转矩和刀盘转速等技术指标。研究结果表明,在其他因素参数一样的条件下,TBM刀具的单周磨损量与围岩的磨蚀性CAI值、强度基本呈线性关系。刀具的单周磨损量随围岩强度和磨蚀性的增大而增大。而当刀盘扭矩和刀盘转速增大时,刀具的单周磨损量先增大后减小。     

Utilizing rock mass properties for predicting TBM performance in hard rock condition

The key parameters on the estimation of tunnel-boring machine (TBM) performance are rock strength, toughness, discontinuity in rock mass, type of TBM and its specifications. The aim of this study is to both assess the influence of rock mass properties on TBM performance and construct a new empirical equation for estimation of the TBM performance. To achieve this aim, the database composed of actual measured TBM penetration rate and rock properties (i.e., uniaxial compressive strength, Brazilian tensile strength, rock brittleness/toughness, distance between planes of weakness, and orientation of discontinuities in rock mass) were established using the data collected from one hard rock TBM tunnel (the Queens Water Tunnel # 3, Stage 2) about 7.5 km long, New York City, USA. Intact rock properties were obtained from laboratory studies conducted at the Earth Mechanics Institute (EMI) in the Colorado School of Mines, CO, USA. Based on generated database, the statistical analyses were performed between available rock properties and measured TBM data in the field. The result revealed that rock mass properties have strong affect on TBM performance. It is concluded that TBM performance could be estimated as a function of rock properties utilizing new equation (r = 0.82).     

Multifactorial fuzzy approach to the penetrability classification of TBM in hard rock conditions

Rate of penetration of a tunnel boring machine in a hard rock environment is generally a key parameter which expresses the ease or difficulty with which the rock mass can be excavated. In this paper, the penetrability of TBM in hard rock conditions was investigated with the developed fuzzy classification system. TBM penetration rate and rock properties (such as Uniaxial Compressive Strength (UCS), Brazilian Tensile Strength (BTS), rock brittleness/toughness, Average Distance between Planes of Weakness (DPW) and orientation of discontinuities in rock mass) were evaluated by using the multifactorial fuzzy approach which is a special case of multiple objective multifactorial decision making for the penetrability classification of TBM in hard rock conditions. Using the decision function, the penetrating performance of TBM was classified into three categories; Good, Medium and Poor. Eventually, it is possible to evaluate the penetrability and determine the advance rate for new conditions by carrying out the proposed rock properties tests and using the developed fuzzy classification system.     

Numerical modelling of the effects of joint spacing on rock fragmentation by TBM cutters

The influence of joint spacing on tunnel boring machine (TBM) penetration performance has been extensively observed at TBM site. However, the mechanism of rock mass fragmentation as function of the joint spacing has been scarcely studied. In this study, the rock indentation by a single TBM cutter is simulated by using the discrete element method (DEM), and the rock fragmentation process is highlighted. A series of two-dimensional numerical modelling with different joint spacing in a rock mass have been performed to explore the effect of joint spacing on rock fragmentation by a TBM cutter. Results show that the joint spacing can significantly influence the crack initiation and propagation, as well as the fragmentation pattern, and can hence affect the penetration rate of the TBM. Two crack initiation and propagation modes are found to fragment the rock mass due to the variation of joint spacing. The simulation results are analyzed and compared with in situ measurements.     

评价岩石脆性指标对滚刀破岩效率的影响

 脆性是岩石重要的力学性质之一。岩石脆性与滚刀破岩效率密切相关,但目前还没有统一的用于评价滚刀破岩效率的岩石脆性指标。总结现有的35种脆性指标,将其分为基于强度、应变、应变能、硬度、莫尔包络线、特殊试验和其他等7种类型。为研究岩石脆性与滚刀破岩效率之间的关系,通过滚刀贯入试验,引入归一化比能概念,提出表征岩石脆性的新指标,重点研究基于强度和贯入试验的脆性指标与归一化比能之间的关系。试验结果表明：(1) 滚刀更难贯入高强度岩石;(2) 脆性指标B2和B4与归一化比能之间呈强烈的指数函数关系,随着脆性的增高,归一化比能降低,滚刀破岩效率增高,应优先选用脆性指标B2来评价滚刀破岩效率,其次是脆性指标B4;(3) 将单轴抗压强度约20 MPa定义为单轴抗压强度过渡值,滚刀不适宜切削单轴抗压强度小于20 MPa的软岩。试验结果对评价滚刀破岩效率时岩石脆性指标的选取具有一定的指导意义。     

高强度围岩隧洞TBM刀具磨损规律研究

刀具磨损是影响TBM掘进效率的重要因素,该文以北疆供水二期工程XEVⅢ标段隧洞为依托,开展高强度围岩条件下刀具磨损规律研究。该标段已掘进段围岩强度最大为160MPa,平均为120MPa。根据掘进过程中的刀具磨损统计资料,分析不同刀位的刀具磨损值、围岩强度和掘进参数对刀具磨损的影响以及不同掘进参数对刀具磨损的敏感度,结果表明:中心滚刀和正面滚刀的累计磨损量随安装半径增大呈指数式增长,边缘滚刀累计磨损量受安装角度影响,随安装半径增大先增大后减小;边缘滚刀的单刀磨损量最大,正面滚刀次之,中心滚刀最小;随着围岩强度提高,中心滚刀和正面滚刀每延米磨损量呈指数型增长,边缘滚刀每延米磨损量呈二次函数型增长,所有刀具每延米累计磨损量呈线性增长;围岩强度不变时,随着刀盘转速、刀盘扭矩、推力、贯入度增大,刀具每延米磨损量均呈二次函数型变化,先增大后减小,随着掘进速度增大,刀具每延米磨损量呈二次函数型变化,先减小后增大;刀具磨损对刀盘扭矩和推力最为敏感,为减小磨损,建议施工中将刀盘扭矩控制在1100～1300kN·m或2100～2400kN·m,将推力控制在9000～11000kN或15000～16000k...     

Numerical modeling of the effects of joint orientation on rock fragmentation by TBM cutters

The performance of tunnel boring machines (TBM) highly depends on the fragmentation efficiency of the cutters. Many geological factors can influence the rock fragmentation process. In this study, a series of two dimension numerical modeling were performed using the discrete element method (DEM) to explore the effect of joint orientation on rock fragmentation by a TBM cutter. Results show that the joint orientation can significantly influence the crack initiation and propagation as well as the fragmentation pattern, and hence affect the penetration rate of the TBM. Such observations are also noted by laboratory and site studies. It also indicates that discontinuum-based DEM has the potential in simulating rock indentation and fragmentation by TBM cutters when rock joints are taken into consideration.     

围压对TBM滚刀破岩影响的数值模拟研究

采用一种新的无网格数值计算方法—广义粒子动力学法(GPD),研究了水平方向围压为0,5,10,15,20 MPa条件下,全断面隧道掘进机(TBM)滚刀的破岩过程及破岩模式,分析了围压对岩体可掘性的影响。得到:(1)围压的存在抑制中央裂纹的扩展;(2)随着围压的增加,赫兹裂纹的扩展方向发生偏转,与水平面的夹角变小;(3)相同贯入度下,随着围压的增加,滚刀法向力及其掘进指数均增加。利用GPD法分析了锦屏二级水电站隧道施工中,含节理的岩层中高地应力对TBM滚刀破岩的影响,成功模拟出高地应力下节理岩体的板裂化现象,得到高地应力能够使岩体产生板裂化促进滚刀破岩。     

不同TBM掘进速率下洞室围岩开挖扰动区研究

 在不同卸荷速率下三轴加卸载室内试验成果的基础上,以Hoek-Brown经验强度准则为依据,拟合出在不同卸荷速率下板岩的力学参数(黏聚力和内摩擦角)。在分析TBM掘进特点的基础上,提出能反映其特点的数值模拟方法,并在FLAC3D程序中引入加卸载准则,对不同掘进速率下隧洞围岩的开挖扰动效应进行数值模拟研究。结果显示：掘进速率越快,围岩开挖扰动效应越小,围岩越稳定;隧洞围岩在开挖后变形较为均匀;在隧洞的径向,位移和应力变化较为明显的呈现为3个区域,即强变化区、弱变化区和平稳区;最大主应力随着洞径方向逐渐由单向应力状态向二向应力状态和三向应力状态转变,第二偏应力不变量在隧洞轴向方向形成一闭合的应力集中区域,称为“应力墙”,该区域在TBM掘进过程中对刀头切割岩体达到破岩的效果极为有利;隧洞围岩开挖扰动区随TBM掘进速率变化较大,当掘进速率增加一倍后,其扰动区由1.1 m降低到0.4 m,减小了64%。     

In situ TBM penetration tests and rock mass boreability analysis in hard rock tunnels

Boreability is popularly adopted to express the ease or difficulty with which a rock mass can be penetrated by a tunnel boring machine. Because the boreability is related to the rock mass properties, TBM specifications and TBM operation parameters, an accurately definable quantity has not been obtained so far. In order to analyze and compare rock mass boreability, a series of TBM shield friction tests were conducted in a TBM tunneling site. Two sets of TBM penetration tests were performed in different rock mass conditions during tunneling in rock. In each step of the penetration test, the rock muck was collected to perform the muck sieve analyses and the shape of large chips was surveyed in order to analyze the TBM chipping efficiency under different cutter thrusts. The results showed that a critical point exists in the penetration curves. The penetration per revolution increases rapidly with increasing thrust per cutter when it is higher than the critical value. The muck sieve analysis results verified that with increasing thrust force, the muck size increases and the rock breakage efficiency also increases. When the thrust is greater than the critical value, the muck becomes well-graded. The muck shape analysis results also showed with the increase of the thrust, the chip shape changes from flat to elongated and flat. The boreability index at the critical point of penetration of 1 mm/rev. defined as the specific rock mass boreability index is proposed to evaluate rock mass boreability.     

自由面对滚刀破岩机制影响的数值模拟研究

为了研究自由面对滚刀破岩机理的影响,运用UDEC方法建立了滚刀贯切岩石的二维数值系列模型,对TBM滚刀破岩过程进行了仿真。分析表明：在合理的刀间距和贯人度情况下,破碎坑自由面的存在使裂纹扩展能耗降低,裂纹密度增大,起裂方式增多,容易实现体积破碎,提高滚刀破岩效率。     

含水量对沉积岩力学性质及其冲击倾向性的影响

 通过试验和统计分析系统研究不同含水条件下煤系沉积岩石力学性质及其冲击倾向性,建立岩石力学性质及其冲击倾向性与含水量之间的相关关系和模型,揭示含水量对岩石力学性质及其冲击倾向性的控制机制。研究表明：岩石单轴抗压强度和弹性模量值随含水量的增加而降低;不同岩性岩石单轴抗压强度和弹性模量值受含水量的影响程度不同,降低的速率受岩性所控制。在干燥或较少含水量情况下,应力–应变曲线在峰值强度后岩石表现为脆性和剪切破坏,具有明显的应变软化特性,且随着含水量的增加,峰值强度后岩石主要为塑性破坏,应变软化特性不明显。随着含水量的增加,岩石脆性指标修正值(BIM)逐渐增加,弹性变形指数逐渐减小,岩石在受力过程中储存的弹性应变能随含水量的增加而急剧减少,而消耗的塑性永久变形能相对增加,即岩石的冲击倾向性随含水量的增加而显著降低。     

高地应力作用下大理岩岩体的TBM掘进试验研究

滚刀破岩效率的研究主要集中在室内线性试验机破岩试验和数值分析2个方面,在工地开展TBM掘进试验尚不普遍。锦屏二级水电站采用3台TBM开挖隧道群,3台TBM在不同洞深(不同地应力)条件对大理岩岩体进行TBM掘进试验、岩石渣片筛分试验及大渣片统计分析,研究岩体条件、TBM机器参数、TBM运行参数对TBM掘进速度的影响及高地应力作用下岩体可掘性指数的变化。研究结果表明:在高地应力条件下,尽管TBM掘进速度随推力增加而增大,但推力超过一定值后,TBM并不在优化状态下运行,TBM的运行需与岩体条件及地应力条件相匹配。     

基于应力–应变曲线的岩石脆性特征定量评价方法

 脆性是岩石的一种重要性质,岩石的许多力学行为都与其脆性有关。总结现有的基于强度、应力–应变曲线、加卸载试验、硬度、矿物成分等脆性指标,并详细分析这些指标在评价岩石脆性时的局限性。为合理、准确评价岩石的脆性程度,提出一种建立在应力–应变曲线峰后应力降的相对大小和绝对速率基础上、能够考虑岩石塑性屈服特性和应力状态影响的新的脆性指标,并开展单轴和三轴压缩实验对新指标进行检验。试验结果表明：水泥砂浆和大理岩脆性程度均随围压增大而减小,相同应力状态下大理岩脆性程度均大于水泥砂浆,这与二者实际脆性程度相符;单轴试验条件下灰岩、大理岩、花岗岩和红砂岩的脆性程度依次减小,破坏时的轴向应变逐渐增大,这与“应变越低脆性程度越大”吻合。试验结果可很好地验证该脆性指标的可靠性,研究成果对丰富和改进现有的岩石脆性特征评价方法具有重要意义。