A Critical Assessment of Dynamic Rock Reinforcement and Support Testing Facilities

A major engineering challenge for mines experiencing significant seismicity is the performance of the support systems. This paper provides a critical review of dynamic testing techniques used for understanding and quantifying the performance of ground support systems. This review focuses on testing rigs in Canada, Australia and South Africa. The different laboratory testing rigs are listed along with their characteristics and their advantages and disadvantages. The paper concludes with recommendations towards developing a more unified strategy to understand and eventually forecast the behaviour of support systems under dynamic loads.     

Fragmentation during Rock Falls: Two Italian Case Studies of Hard and Soft Rocks

In recent years, rock fall phenomena in Italy have received considerable attention for risk mitigation through in situ observations and experimental data. This paper reports the study conducted at Camaldoli Hill, in the urban area of Naples, and at Monte Pellegrino, Palermo, Italy. The rocks involved are volcanic Neapolitan yellow tuff (NYT) in the former area and dolomitic limestone in the latter. Both rocks, even though with different strength characteristics, have shown a significant tendency towards rock fragmentation during run out. This behavior was first investigated by comparing the volumes of removable blocks on the cliff faces (V ₀) and fallen blocks on the slopes (V _f). It was assumed that the ratio V _f/V ₀ decreases with the distance (x _f) from the detachment area by an empirical law, which depends on a coefficient α, correlated with the geotechnical properties of the materials involved in the rock fall. Finally, this law was validated by observation of well-documented natural rock falls (Palermo) and by in situ full-scale tests (Naples). From the engineering perspective, consideration of fragmentation processes in rock fall modeling provides a means for designing low-cost mitigation measures.     

岩石破坏后的注浆固结体的力学性能

在破裂岩石残余强度和变形性能研究的基础上,进一步开展其注浆固结体的力学性能试验研究。试验证实注浆固结后破裂岩块残余强度有不同程度的提高,同时发现其侧向变形和径向变形趋向协调,从而提高了破裂岩块的塑性变形性能,并在较大变形范围内保持稳定的承载能力。试验结果有助于解释围岩注浆加固控制巷道变形的机理。     

节理岩体中锚索加固作用分析

简要介绍了锚索加固技术的应用,并对全长粘结式锚索在节理岩体中的锚固作用机理进行初步分析,同时对节理岩体中锚索加固的抗拉粘结强度及抗剪切强度的影响因素进行了分析。     

江西马当长江堤防抛石加固施工技术

抛石固岸是崩岸除险的一种常用方法,本文结合江西马当长江堤防加固工程介绍该施工技术.     

关键块体系统锚固法在加固边坡危岩中的应用

基于Goodman-Shi的块体理论和A.R.Yarahmadi Bafghi的关键块体群理论,提出确定危岩边坡关键块体和关键块体系统的几何分析法和矢量分析法,建立边坡危岩的地质模型和力学模型,分析危岩体破坏机理,针对不同变形破坏机理的关键块体系统提出合理、安全和经济的危岩边坡加固新方法--关键块体系统锚固法（KSA法）。通过建立集丹公路K49+790 m-K55+550 m段危岩边坡的地质模型和力学模型,结合其坡体及岩体结构特征,分析边坡危岩体变形破坏机理和锚固机理,提出顶部危岩清除、碎裂结构坡面喷射混凝土、块裂结构坡面挂网和块状岩体锚固的清-喷-网-锚联合锚固的系统锚固方案,加固该段危岩体。运用该法锚固方案较传统方法节省锚杆35%、SNS网32%及腰梁19%。     

Study on Rock Bolt Reinforcement for a Gravity Dam Foundation

In this article, the rock bolt reinforcement mechanism is discussed, and the gravity method as well as the finite element method for the bolted rock is presented. These methods are applied to study the gravity dam foundation of the Xiaoxi Hydropower Project, which is influenced by the presence of a large fault with a cracked zone over 180 m wide. Rock bolt reinforcement was used to improve the stability of the dam foundation, and the reinforcement parameters were determined from a semi-empirical equation controlled by in situ test. The stability analysis was conducted using the above methods, and the improvement in terms of deformation and stress as well as stability of the dam foundation due to the reinforcement is assessed. Rock bolt reinforcement was completed successfully, and the dam started normal operations in January 2008.     

新型岩石力学测试系统及应用领域

介绍了Ｔｅｒｅａ Ｔｅｋ系统的组成和其主要功能，并针对石油工程和钻探领域应用岩石力学参数领域作了阐述。     

Effects of Testing Conditions on Intact Rock Strength and Variability

The strength of intact rock is a fundamental and integral part of many aspects of engineering and geologic practice. It is necessary to understand how testing conditions influence this strength and its variability, especially for use in reliability-based design. In this study, the effect of sample diameter and moisture content on the strength and its variability was examined in detail. Correlations are given for assessing the effect of sample diameter on the laboratory uniaxial compressive strength (q_u), Brazilian indirect tensile strength (q_t-Brazilian), and point load strength (I_s), and the associated direct correlations among these tests. Correlations also are given for assessing the effect of sample moisture content on q_u, q_t-Brazilian, and I_s. The statistics of data scatter suggest these correlations can introduce large uncertainties. The effect of sample diameter and moisture content on the coefficients of variation was examined subsequently, and it was found to be relatively minor.     

缓倾角顺层滑坡失稳机制及加固措施研究

本文通过某缓倾角顺层岩质滑坡实例,分析了该滑坡的变形破坏特征,并通过建立FLAC3D数值模型研究滑坡产生的原因、失稳机制和松弛区影响范围,结果表明:1.滑坡破坏模式属于张拉-剪切复合破坏,基于张拉-剪切复合破坏准则对岩质边坡进行稳定性分析更符合实际。2.FLAC3D数值计算能确定边坡开挖产生的松弛区影响范围,结合极限平衡法可用于分析该类型边坡的稳定性。3.此类工程采用预应力锚索对滑坡进行加固处理能够较好地控制滑坡位移,施工阶段对滑坡的扰动也较小,安全性较高,同时能够降低工程造价,较经济。     

Grouting Material for Broken Surrounding Rock and its Mechanical Properties of Grouting Reinforcement

Geotechnical and Geological Engineering - Aiming at the shortcomings of traditional grouting materials, such as large influence on water content, large volume shrinkage in the late stage, poor...     

The Use of Rock Mass Classification Systems to Estimate the Modulus and Strength of Jointed Rock

Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the measured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confidence in the use of classification schemes to estimate the deformation and stability in jointed rock.     

Analytical and Numerical Study of the Mechanics of Rockbolt Reinforcement around Tunnels in Rock Masses

Summary  This paper addresses the problem of quantifying the mechanical contribution of rockbolts installed systematically around tunnels excavated in rock masses. The mechanical contribution referred to here is that of increased stress confinement and decreased tunnel convergences as compared with corresponding stresses and displacements obtained for non-reinforced tunnels. The problem is treated analytically first by presenting a closed-form solution for stress and displacement distributions around a circular tunnel excavated in elastic material and reinforced by grouted or anchored rockbolts. The analytical solution assumes that rockbolts are regularly spaced around the tunnel and that axi-symmetry conditions of geometry and loading apply. The results obtained with the closed-form solution are shown to be equivalent to the results of the same problem solved with traditional numerical methods. Based on the analytical and numerical results and by introducing dimensionless ratios that allow to quantify the increase of radial stresses and the decrease of radial displacements in the reinforced region of the tunnel, the paper shows that reinforcement can have a significant mechanical effect (i.e., increasing the confinement and decreasing the convergences) in tunnels excavated in rock masses of poor to very poor quality. The paper analyzes then the mechanical contribution of rockbolt reinforcement when the rock mass is assumed to behave elasto-plastically. For this case, it is shown that rockbolt reinforcement can also have a critical effect in controlling the extent of the plastic failure zone and the convergences of the tunnel. Correspondence: C. Carranza-Torres, Department of Civil Engineering, University of Minnesota, Duluth Campus, 1305 Ordean Court, Duluth, USA     

A Review of the Tensile Strength of Rock: Concepts and Testing

A review of the tensile strength of rock was conducted to determine the relationship between direct tensile strength (DTS) and Brazilian tensile strength (BTS) and to examine the validity of estimating tensile strength from other measured properties, such as the crack initiation (CI) threshold. A data set was gathered from the existing literature where tensile values could be reliably correlated with unconfined compressive strength or CI values. It was determined that the BTS obtained in standard testing is generally greater than the equivalent DTS and that this relationship is rock type dependent. CI yields a reasonable estimate of tensile strength and this correlation is improved when the BTS values are reduced to DTS values by rock type specific correlations. The factor f, in DTS = f BTS, can be considered to be approximately 0.9 for metamorphic, 0.8 for igneous and 0.7 for sedimentary rocks. The relationships presented demonstrate that there is wide scatter in the available data for estimating tensile strength likely due to both specimen variability and testing configuration, including platen geometry and relative stiffness. Estimates of tensile strength should only be used for preliminary design purposes and measurements should be made to confirm preliminary assumptions for each design.     

Investigation of Flexural Behavior of Geocell Reinforcement Using Three-Layered Beam Model Testing

The study presented in this paper aimed to investigate the flexural behavior of geocell reinforcement by means of three-layered beam model testing. The geocell reinforcement was assumed to be a continuous beam sandwiched between two identical polywood beams. An analytical analysis was conducted to derive the closed-form solution to calculate the deflection of the three-layered beam model. A series of four-point bending tests using dead weights were carried out to test the three-layered beam models. Two geocell products of different dimensions and two types of infill materials, crushed stone and silty sand were tested in this study. Deflections of the layered beam models were measured along with the increment of applied loads. Testing results showed that the geocell reinforcement provides considerable resistance to flexural deformation, especially at higher load levels. The geocell with greater cell height to cell length ratio exhibited overall greater resistance to flexural deflection, especially when crushed stone was used as infill materials. Geocell reinforcements filled by crushed stone showed less flexural deformation than the geocells filled by silty sand. The modulus of the geocell reinforcement was calculated based on the closed-form solution and deflection measurements from the four-point bending tests. Ranges of elastic modulus were presented for the geocell reinforcement filled with compacted crushed stone and silty sand, which can be used as reference values for material property inputs in mechanistic-empirical design of geocell-reinforced pavements.     

碳酸盐岩烃源岩判识与实践——以四川盆地为例

碳酸盐岩可以成为烃源岩,并为油气藏提供丰富的烃源,但不是所有碳酸盐岩都可以视为烃源岩。碳酸盐岩在成藏进程中,往往作为输导层或储集层,并常有外源有机质的干扰。碳酸盐岩烃源岩应该是有机质原生赋存(与矿物结合成为沉积的一部分),具有一定丰度值,在适宜的热成熟阶段,同样可以形成液态烃和气态烃。碳酸盐岩烃源岩发育于低能环境的沉积相——开阔海台地相、局限海台地相、生物泥丘相、斜坡相,等等。泥质泥晶灰岩,生物泥—粒泥岩—泥粒岩微相,应该是碳酸盐岩烃源岩的主要岩类。碳酸盐岩烃源岩与油系泥质烃源岩比较,具有油窗凸显且高峰期前移、气态烃峰期不明显且有后延、液态烃产率高的特点。据对碳酸盐岩烃源潜量的评估,它在四川盆地烃源中占20%～25%,为油气成藏作出了重要贡献。