复合地层隧道围岩强度实时估算研究

隧道TBM开挖过程中经常会遇到复合岩层,在这种地质环境下,隧道掘进机（tunnel boring machine,简称TBM）开挖过程中的隧道围岩强度很难估计,隧道开挖掌子面和围岩容易发生坍塌。为了提高隧道掘进效率、预防事故发生,对开挖隧道围岩强度进行实时估算方面的研究很有必要。在重庆轨道九号线隧道TBM施工中,通过室内试验和现场实测数据发现,TBM推力F_N与岩石强度成正比、TBM扭矩推力比T/F_N（T为扭矩）与贯入度p^0.5成正比例关系。针对砂质泥岩、砂岩和灰岩组成的复合岩层,提出了一种利用现场实测推力F_N和扭矩T的值来快速估算开挖隧道围岩强度的方法,进一步对TBM实测数据进行线性拟合,从而得到估算公式中两个常数α₁、α₂的取值方法,并在10多个隧道实际工程中得到验证。结果表明,对于这种复合岩层地质环境,两个常数α₁、α₂的值与滚刀数量n和滚刀直径d相关。该研究成果为实时快速估算开挖隧道围岩强度提供了一种新的切实可行的思路,能提高隧道TBM施工的可靠性和安全性,具有重要的应用价值。     

Artificial neural network model for prediction of rock properties from sound level produced during drilling

In many rock engineering applications such as foundations, slopes and tunnels, the intact rock properties are not actually determined by laboratory tests, due to the requirements of high quality core samples and sophisticated test equipments. Thus, predicting the rock properties by using empirical equations has been an attractive research topic relating to rock engineering practice for many years. Soft computing techniques are now being used as alternative statistical tools. In this study, artificial neural network models were developed to predict the rock properties of the intact rock, by using sound level produced during rock drilling. A database of 832 datasets, including drill bit diameter, drill bit speed, penetration rate of the drill bit and equivalent sound level (L_eq) produced during drilling for input parameters, and uniaxial compressive strength (UCS), Schmidt rebound number (SRN), dry density (ρ), P-wave velocity (V_p), tensile strength (TS), modulus of elasticity (E) and percentage porosity (n) of intact rock for output, was established. The constructed models were checked using various prediction performance indices. Goodness of the fit measures revealed that recommended ANN model fitted the data as accurately as experimental results, indicating the usefulness of artificial neural networks in predicting rock properties.     

顺层岩质边坡锚杆拉剪作用力学性能

锚杆能够显著增强顺层岩质边坡的稳定性.基于顺层边坡结构效应,应用锚杆加固顺层边坡的力学模型,根据结构力学理论和变形协调关系,建立拉剪作用下全长粘结型锚杆加固顺层边坡抗剪计算的理论分析方法.与相关试验数据进行了比较验证,结果表明顺层边坡锚固抗力模型计算结果与试验结果比较一致,验证了理论模型的合理性.讨论了锚杆倾角、锚杆直径、灌浆体强度、结构面内摩擦角、剪胀角等对加锚顺层岩体抗剪性能的影响.分析表明:锚杆锚固抗力模型能够较好地反映锚杆轴力及横向剪切力对顺层岩质边坡的抗剪作用.锚杆倾角越大,锚杆总的抗力呈减小趋势,而锚杆抗力随剪胀角增大而增加;当锚杆倾角等于内摩擦角时,锚杆抗力达到最大;锚杆抗力随锚杆直径增加而增大;当锚杆直径不变时,锚杆抗力随灌浆体抗压强度增大而有所减小.      

Multi-scale rock surface area quantification—a systematic method to evaluate the reactive surface area of rocks

An integration of methods to quantify the surface area of porous solid materials with a broad span of spatial resolution is presented. The application of it is to detect and quantify the rock surface area modifications caused by fluid-rock interactions on different scales from several nanometres to metres. The new approach is to study the fluid-accessible surface area of rock fragments during dissolution processes.In this paper, diverse methods for surface quantification at different levels of surface detail were adapted for the application of rock surface quantification and porosimetry measurements. The geometric external surface area of rock fragments can be determined by paraffin wax coating and, in special cases, by parallelepiped surface estimations. This geometrical surface area of rock polyhedrons is equal to the macroscopic bounding surface area of a rock volume. Representative surface details on the scale of micrometres to millimetres on geometrical surface area can be quantified by mechanical roughness analyses. The resultant roughness factors are compared to optical roughness quantifications by confocal laser scanning microscopy and white light interferometry and can indicate modifications of the pore space up to several hundred nanometres. The comparison of rock pore space data, measured by both mercury intrusion porosimetry and nitrogen adsorption, quantifies the surface area of pores with a diameter of approximately 2 nm.These various surface data at different levels of detail were integrated to get an estimation of this surface area, which affects fluid-rock interactions. The proposed concept has the potential to trace the multi-scale rock surface area evolution in response to fluid-rock interaction processes.The importance of this concept is its application beyond the laboratory survey. For example, additionally to their specific surface area, the reactive surface area of rock particles in a mining dump is controlled by geometrical size and surface roughness of particles.     

The Investigation of Twin Tunnel Stability: Effect of Spacing and Diameter

The underground excavation became the backbone of developing as well as developed country due to unavailability of surface area and increase demand of space for transportation, water channeling, waste disposal and storage. Except for transportation, the crystalline rocks (high strength, low porosity and less permeability) are considered most suitable and safe space for the storage of radioactive waste as well as petroleum. The role of spacing between twin tunnel and tunnel’s diameter in its stability was carried out using finite element method. Not much research has been done on twin tunnel spacing in hard rock. In the present study, a total of ninety simulations were performed to investigate critical spacing of the twin tunnel in granitic rock mass. Twin tunnel diameter is varied from the 2 m to 10 m and their spacing varied from 0.2 to 2 times of diameter. It was concluded that minimum spacing should be 0.8 times of the tunnel diameter. It was also found that small diameter tunnel effects only near field but large diameter tunnel effect near field as well as far field. The vertical hole, approximately 3m diameter, containing radioactive waste canister should be drilled at the interval of more than 2.4m.     

A Statistical Approach to Predict the Effect of Confinement on the Detonation Velocity of Commercial Explosives

Summary Commercial explosives behave non-ideally in rock blasting. A direct and convenient measure of non-ideality is the detonation velocity. In this study, an alternative model fitted to experimental unconfined detonation velocity data is proposed and the effect of confinement on the detonation velocity is modelled. Unconfined data of several explosives showing various levels of non-ideality were successfully modelled. The effect of confinement on detonation velocity was modelled empirically based on field detonation velocity measurements. Confined detonation velocity is a function of the ideal detonation velocity, unconfined detonation velocity at a given blasthole diameter and rock stiffness. For a given explosive and charge diameter, as confinement increases detonation velocity increases. The confinement model is implemented in a simple engineering based non-ideal detonation model. A number of simulations are carried out and analysed to predict the explosive performance parameters for the adopted blasting conditions.     

小三峡岩溶隧道围岩防突层安全厚度有限元分析

针对小三峡隧道岩溶发育的工程地质特征,采用有限元方法建立典型隧道断面数值计算模型,分析充水溶洞位于隧道不同方位、不同距离时隧道围岩位移和塑性区变化规律,并结合围岩的位移变化情况和塑性区分布情况作为评价隧道围岩突水的判据,得出防止隧道围岩突水的岩层最小安全厚度。研究结果表明:在岩溶水压力作用下,当洞径比一定时,随着溶洞逐渐远离隧道,溶洞对隧道的影响在逐渐减弱;当间径比一定时,溶洞直径越大对隧道的影响越明显;同时根据围岩的位移和塑性区计算结果得到了隧道围岩最小防突厚度。研究成果可为小三峡隧道安全施工提供技术支撑。      

Preliminary support design for Ankara subway extension tunnel

This paper presents the results of preliminary support design of the subway tunnel for Ankara subway project in accordance with some empirical and numerical methods, using the phase 2D finite element method (FEM). The 5 m diameter subway tunnel will advance through slightly to moderately weathered dacite and weak zones. Rock masses were characterized in terms of rock mass rating (RMR), geological strength index (GSI) and Q System. Core samples were tested in the rock mechanics laboratory to determine uniaxial compressive strength, deformability parameters, unit weight, tensile strength and triaxial compressive strength properties. Finally, rock mass strengths were determined by empirical and numerical methods. Required support system was suggested.     

Measurement and analysis of near-field blast vibration and damage

Summary Blast vibration and its attenuation within the rock mass immediately adjacent to a blast hole (2–15 m) were monitored for a blast hole diameter of 100 mm and a 2.4 m column of an emulsion explosive charge. Peak particle velocities calculated from the measured accelerations were compared with predictions from the charge-weight scaling law using typical site parameters which would be adopted for many far-field vibration predictions. It was found that the vibration amplitudes predicted by the conventional charge-weight scaling law are significantly lower than measured values. Strain and strain rates at different monitoring holes were calculated from experimental data. Using attenuation analysis of different frequency bands of measured acceleration signals, it was found that blast vibration attenuation between 2 m and 4 m depended not only on frequency but also on amplitude. A failure wave was postulated based on observations at the monitoring hole 2 m from the blast. A blast damage zone was evaluated using borehole camera and cross hole seismic studies. The damage zone in the rock was also analysed according to acceleration waveforms measured at different monitoring locations. The use of different techniques to measure blast damage provided an accurate assessment of the blast damage volume.     

三峡库区箭穿洞危岩体变形破坏模式与防治效果分析

本文以三峡库区箭穿洞危岩体为例,对涉水厚层危岩体的变形破坏模式和防护措施进行了研究。根据现场调查和长期监测数据可知,干湿循环作用下基座岩体的劣化是加速箭穿洞危岩体变形破坏的主导因素,并判定其破坏模式为基座滑移式崩塌。在此基础上,将危岩体的防护治理定为两部分,分别是基座软弱岩体的补强加固,以及中上部危岩体的锚索加固。通过数值模拟对防护前后危岩体的位移场以及应力场进行了分析,结果表明危岩体上部的锚索加固能够有效控制岩体的变形,基座补强能够有效控制危岩体的最大剪应力,综合防护可以显著提高箭穿洞危岩体的稳定性。该防护措施的理念及方法,可以为库区涉水危岩体的治理提供重要的参考价值。     

Size and stress gradient effects on fracture around cavities

Summary The effect of hole size on fracture initiation around cavities in rock is examined through physical model tests on Tyndall limestone. Twenty five models, employing nine different hole sizes, ranging from 3.2 to 62 mm in diameter were tested in uniaxial compression. Strain gauges placed both on the face of the model block and inside the cylindrical cavity were used to record the state of fracture.Fracture initiation data for primary, remote and sidewall fractures were determined using the stress-strain curves from the respective strain gauge locations. For all three fracture types, the initiation stress decreases with increasing hole size and appears to approach a horizontal asymptote for large cavity sizes. The fracture mechanics formulations and the stress averaging method give the best fit to the primary fracture initiation except for very small cavity sizes. The stress averaging method also provides a very good fit to the sidewall fracture initiation data.     

A new concept for sinking freeze shafts into great depths

For Ruhrkohle AG, the largest mining company of the Federal Republic of Germany, nine shafts are presently being sunk. In late 1978, Gewerkschaft Walter, Essen, obtained the contract for the construction of the Voerde shaft from Bergbau AG Niederrhein, a subsidiary of Ruhrkohle AG.

The requirements to be met regarding the quality of the lining in terms of loads to be absorbed from rock pressure, hydraulic pressure, tension, etc. are very high. Up to a depth of 600 m, this shaft will be sunk through soft and water-bearing strata such as formations of Tertiary, Cretaceous, Bunter Sandstone and Permian. The freezing method therefore has to be employed.

The high requirements with regard to the quality of the lining can only be fulfilled if the lining is constructed in the form of an absolutely watertight tube, not connected to the surrounding ground and resting on a ring foundation below the frozen part of the shaft.

During sinking of the shaft, the icewall will normally absorb the load of both rock pressure and hydraulic pressure. Because of the depth of the frozen part of this shaft and for economical reasons, a yielding outer lining has to be constructed. This will serve on one hand as an auxilliary lining during sinking as a support for the icewall and, as part of the final lining on the other hand, will absorb the rock pressure. This auxilliary lining can only be of the yielding type, its flexibility must correspond to the behavior of the surrounding frozen rock. The determination of the thickness of the icewall and the outer lining was based upon results of tests carried out on frozen and non-frozen drilling cores by Prof. Jessberger's Institute at the Ruhr-University of Bochum.

Taking an outside shaft diameter of approximately 9 m, the diameter of the freezingpipe circle is 18.5 m, the number of freezing pipes is 38.

Considering an icewall-thickness of 8 m (on average) and using the data for friction and cohesion for the different rock formations resulting from the above mentioned tests, the lining dimensions for the different rock formations were calculated. The determined dimensions were widely varying. It also had to be considered, that the outer lining would have to bear the load of the rock pressure once the frozen core of the shaft had been finished.     

我国首例典型超基性-碱性-碳酸岩杂岩体及磷矿的发现

通过40年前验证马伸桥航磁异常获得的隐伏超基性碱性岩体钻孔原始编录等资料的综合分析研究,发现了岩体深部为火成碳酸岩体,从而确立为我国首例典型超基性岩-碱性岩-碳酸岩三位一体的杂岩;发现超基性岩为一多韵律的层状岩系;发现9个磷矿层,累积厚度68.25m,P2O5含量6%¹2.6%,已构成大型中品位磷灰石矿床。马伸桥杂岩体与矾山杂岩体具有诸多相同或相似性特点,有极大可比性:都是航磁发现的隐伏岩体、围岩为中元古代蓟县系白云岩、产出的地质构造为燕山台褶带、成矿时代为印支期、多韵律的层状岩系、产大型到超大型磷灰石矿……。这才是"矾山式"磷矿的独特特点。     

西藏鸭湖地区天然气水合物调查井钻探施工技术

西藏羌塘盆地是公认的天然气水合物有利找矿区,钻探取心是鉴别天然气水合物最直接、最准确的手段。为满足天然气水合物钻探需求,制定了大直径取心、低温泥浆护心的技术方案。试制了跟管取心钻具和大直径绳索取心钻具;逐步完善低温泥浆配方;研制出新型高效泥浆冷却装置。在鸭湖地区天然气水合物调查井施工中,克服地层复杂、环境恶劣等难题,完成钻探取样施工,终孔深度700.70 m,岩心采取率满足地质要求。查明了地层岩性、冻土厚度、气源、岩石物性特征等,不仅为天然气水合物资源评价也为其他油气资源调查提供了地质资料、技术支撑和人才储备。     

辽宁大连地区中-新元古界砂岩盐风化穴的发现及意义

A small honeycomb tafoni was found on the surface of the Meso-Neoproterozoic sandstone in Wafangdian area, Dalian, Liaoning Province. It is located on the surface of the northwest side of the outcrop sandstone layer. On the top surface of the sandstone layer and on the east and south sides, the tafoni was not developed. The whole tafoni is round or oval, with a diameter of 1-5cm and a depth of 1-2cm. Through field observation and comparative analysis, it is determined that it is the salt weathering tafoni. It is formed by the precipitation and crystallization of salt from sea fog in sandstone, which causes the detrital particles on the rock surface to fall off and weathering.     

Elasto-plastic Behavior of Raghadan Tunnel Based on RMR and Hoek–Brown Classifications

Lining contact pressure and ground deformation of Raghadan transportation tunnel (Amman, Jordan) were investigated. The tunnel is 1.1 km in length and 13.5 m in diameter. This study was intended to integrate useful relations among the widely used rock classification system (RMR: rock mass rating), Hoek–Brown classification, and lining-ground interaction. The materials encountered along the tunnel alignment were limestone, dolomatic limestone, marly limestone, dolomite, and sillicified limestone. The ground conditions along the tunnel alignment including bedding planes, joint sets and joint conditions, rock quality, water flow, and rock strength were evaluated based on the drilled boreholes and rock exposures. Elasto-plastic finite element analyses were conducted to study the effect of rock mass conditions and tunnel face advance on the behavior of lining-ground interaction. The results of the analyses showed that lining contact pressure decreases linearly with the increase in RMR value. Also the results showed that tunnel lining contact pressure and crown inward displacement decreases with the increase in the unsupported distance (distance between tunnel face and the end of the erected lining). Ground displacement above the tunnel crown was found to be increases in an increasing rate with the decrease in the depth above the crown. This displacement was also found to be affected by the RMR value and the unsupported distance.     

Study of the geometrical size effect of a fractured rock mass based on the modified blockiness evaluation method

The determination of representative elementary volume (REV) is critical for mechanical model establishment and the determination of rock mass mechanical properties. Therefore, in this study, the REV range, existence, determinate parameter, and category were discussed. The blockiness level of the rock mass (B_z) was defined as the new index to determine the geometrical rock mass REV. Then, a great variety of multiscale three-dimensional fractured network models with different discontinuity persistences and spacings were developed. Finally, the B_z values of all models were measured, and the geometrical REVs were determined, the correlation between the geometrical REVs and rock mass discontinuity properties were assessed, and size validations of geometrical REVs were performed. In this study, it is shown that the REV is approximately 20–50 times that of the discontinuity spacing when the discontinuity spacing is classified as having extremely close to close spacing and is between approximately 0.3 and 4.0 times the discontinuity diameter when discontinuity spacing is in the range from moderate to extremely wide spacing. Further, there is a fourth-order nonlinear correlation between the geometrical REV and the ratio of the discontinuity diameter to discontinuity spacing. Meanwhile, the validation results confirm that the geometrical REV is slightly less than the sizes at which the elastic moduli tend to plateau, and the rationality of the geometrical REV of a rock mass based on B_z is thus supported from another perspective.     

基于钻孔电视的深部岩体节理三维网络模拟

为了准确模拟岩体节理的空间分布,评价高放废物地质处置库围岩的稳定性,先通过调查露头节理数据,运用概率统计理论进行节理几何特征模拟,再利用Monte-Carlo法来模拟节理空间分布特征,并以高放废物地质处置新疆预选区天湖地段花岗岩体为研究对象,通过钻孔电视调查不同深度节理几何特征,划分钻孔岩体结构均质区,提出钻孔节理产状、大小、密度的统计方法和计算公式,以均质区建立节理三维网络模型并通过数据对比法进行模型验证。结果表明：1）利用列联表卡方检验和重叠窗口法可将天湖钻孔岩体划分为0~90、120~240、270~360和390~600 m等4个均质区;2）利用SPSS软件以及基于节理直径、迹长和隙宽之间的数量关系得出节理产状服从正态分布,节理直径服从负指数分布;3）通过数据对比法得出模型统计和现场测量的节理平均产状数据相差±3°以内,平均直径相差±1 m以内,平均面密度相差±0.01 m^-2以内,从而验证了Monte-Carlo法建立的节理三维网络模拟的准确性。     

Tensile strength and its anisotropy measured by point and line-loading of sandstone

Tensile fracture is an ubiquitous feature of rock failure ranging in size from microfracture around Griffith cracks to the large-scale explosive failure accompanying rock bursts in underground cavities. Hence the resistance of rock to failure in tension, the tensile strength, is one of the fundamental parameters of rock strength. The tensile strength of rock is, however, a most elusive parameter which is difficult to measure and to define.

The tensile strength, and its variation with direction, was determined by the pointloading and the line-loading (Brazilian test) methods for nine rocks from five sandstone formations in New Brunswick, Canada. Altogether 319 double point-load and 357 line-load tests were conducted on discs having a diameter of 22.9 mm and thickness of 7.9 mm.

The tensile strength determined by the point-load test and as calculated by the Frocht formula was found to be consistently lower than that obtained by the line-loading technique. To some extent, the difference is due to the fact that most of the sandstones are anisotropic with respect to tensile strength and that the constraints in the point-load test are such that fracture occurs along the plane of minimum tensile strength; the computed tensile strength therefore represents a minimum value. To a greater extent, the lower tensile strength calculated from the point-load test is due to the difference in the states of stress induced by the two techniques. When correction is made for the anisotropy, the tensile strength from the Brazilian test is still 3.76 times larger than the one obtained from the point-load test.

The Brazilian test seems to yield a more accurate definition of both the tensile strength and its variation with direction. The point-load test is more suitable for the determination of the minimum value of tensile strength and the direction of the preferred fracture plane.