Experimental and Numerical Analysis on Rupture of Rock Bridge with Non-Coplanar Intermittent Joints Under Direct Shear

By using servo control shear loading system, specimens with non-coplanar rock-like intermittent joints were tested by the way of forward and reverse direct shear, rupture mechanism and shearing law for rock bridge with non-coplanar intermittent joints were studied under direct shear. The experimental studies showed that five apparent stages are presented in the process of rock bridge rupture under direct shear, which are linear elastic stage, initiation and extension of crack, fracture and transfixion of rock bridge, climbing and occlusion of shear plane and residual friction. Rock bridge presented profile fracture plane under forward direct shear. While under reverse direct shear, band form fracture plane is showed which penetrated along with the direction of forward shear, and the shear strength of initiation and peak shear strength under reverse direct shear are bigger than that under forward shear. Crack angle, normal stress and lap proportion among adjacent joint are the main factors that influence the initiation strength and peak shear strength. The FLAC 3D simulation for the process of non-coplanar intermittent joints rock bridge rupture and formation of shear rupture surface under forward and reverse direct shear was conducted. The results of numerical simulation agreed well with those of experiment. The simulation results revealed tension crack failure of non-coplanar intermittent joints rock bridge and shear yielding mechanism of fracture plane.     

Elastic-Perfectly Plastic Solution of Tunnel Surrounding Rocks Using Mogi-Coulomb Strength Criterion

Reasonable choice of rock strength criteria is crucial for stress and displacement prediction and support design in tunnel engineering. Based on Mogi-Coulomb strength criterion and elastic-perfectly plastic model, analytical solutions of stress and displacement for surrounding rocks around a circular tunnel were derived The intermediate principal stress coefficient was used to present the intermediate principal stress effect. The results in this study were compared with the current solutions in the literatures and the influence of intermediate principal stress and shear strength parameters of surrounding rocks was discussed. The results showed extensive applicability and the Mohr-Coulomb strength criterion and Matsuoka-Nakai criterion are two special cases; when the intermediate principal stress coefficient b was equals to 0.5, the results indicated that the intermediate principal stress effect and its range for rock strength; the influence of cohesion and internal friction angle on the plastic radius and tunnel wall displacement was significant; Care should be taken to the effects of intermediate principal stress and shear strength parameter variations of surrounding rocks on tunnel design and construction.     

Elastoplastic Analysis of Discrete Jointin Rockmass Loaded by Compress_shear

In this paper the elastoplastic stress fields near joint line in rockmass loaded by compress- shear are analyesd by the line field method in fracture mechanics with Mokr- Coulomb criterion. Through the matching conditions of the elastoplastic fields on their boundary, the relations between the length of plastic zone on the joint line and the compress- shear loads are found, and the fracture criterion of the discrete joint is also obtained     

Brittle material removal mechanism of ultrasonic vibrationassisted grinding

To remove the brittle material in ductile state can help to improve the machined surface quality.Experiments of material removal mechanism for NdFeB are conducted by using tangential ultrasonic vibration assisted grinding,axial ultrasonic vibration assisted grinding and normal ultrasonic vibration assisted grinding.Based on the critical condition of brittle-ductile transition,the effects of different ultrasonic vibration modes on material removal mechanism are analyzed.Results indicate that the material is mainly removed in the form of plastic shear in axial ultrasonic vibration assisted grinding.The material is mainly removed in the form of transgranular fracture,plastic shear and little intergranular fracture in tangential ultrasonic vibration assisted grinding.While in normal ultrasonic vibration assisted grinding,the material is mainly removed in the form of fracture crash and the cracks remain in the machined surface.So axial ultrasonic vibration assisted grinding is the best machining method to realize the ductile grinding on brittle materials.     

A FRACTURE MECHANICS ANALYSIS OF FRACTURE PLANE CONTROL IN FRACTURE CONTROL BLASTING

A procedure of fracture control blasting for achieving directional breaking of rocks by blasting is presented. The criterion for initiating of radial cracks in borehole wall under dynamic load and the method for determining the permissible rang of initial gas pressure (p0) in the charge cavity are developed .and the branching of radial cracks and the effeets of the pressure (p0) and blasthole geometry (R0.a.L3) on final dimensions of directed cracks are studied .with Fracture Mechanics analysis in all three aspects of fracture process including crack initiation .crack propagation and crack arrest.     

Stability analysis method for perilous rock by fracture mechanics

Perilous rock is a type of geological disaster in mountainous areas. Research concerning perilous rock ruptures focuses on the expanding of control fissures in perilous rock under load action. Taking the control fissure in perilous rock as one crevice in a sample, a method employing fracture mechanics is established to calculate the union fracture strength factor along the rupture orientation at the terminus of a control fissure in perilous rock. The union fracture strength factor is a function of both the first and second type fracture strength factors. We define the ratio between the fracture tendency of rock and the union fracture strength factor as the stability coefficient of perilous rock. Further, it simplifies the rupture mechanism of sliding, falling, and toppling perilous rock as pressure shear and tension shear ruptures. We establish methods for calculating the first and second type fracture strength factors. The applications show that the stability status identified by the method is more reasonable and sensitive.     

AN EXPERIMENTAL STUDY ON CEMENT MORTAR SPBCIMENS WITN A CENTRAL SLITS UNDBR UNIAXIAL COMPRESSION

The cement mortar specimens with a central slits are tested under uniaxial com-pression.The test results show that tensile cracks initiate,as a rule near the tip and may propagatesteady for a certain length.Mean while shear fructures appear and propagate slowly to the failurestate in the zone of compressive stress concentration. So the fracture strength of rock under compres-sion might be differentiated into the initial tensile strength,the peak strength and residual strength.     

A Fracture Mechanics Solution for Control Fissures in Perilous Rock under Seepage Stress

Crack propagation of control fissures in perilous rock under loads is a key process in the failure of perilous rock. Based on the loading mechanism, the control fissures are classified into compression shear and tension shear types. By introducing a model of seepage stress, the calculating principle of the stress intensity factor and the propagation orientation of control fissure under seepage stress are put forward using fracture mechanics methods. Using Shoulishan perilous rock in the Wanzhou district of Chongqing, P. R. China, as an example, the calculated results show that there is an obvious increase of the stress intensity factor. The influence of hydrostatic pressure and hydrodynamic pressure also are analyzed.     

限制性剪切蠕变的渐进式破坏发育模式与本构方程分析

以标准红砂岩方形试样为研究对象,运用自行研制开发的软弱煤岩剪切蠕变试验设备和煤岩细观力学特性测控软件、超声波检测设备,对红砂岩限制性剪切、限制性剪切蠕变过程的破坏过程、破坏模式、渐变特性进行了分析。结果表明：红砂岩试样在限制性剪切、限制性剪切蠕变条件下表现出明显的渐变破坏特性;大部分试验过程中试样内部的超声波速减小幅度较小,仅在临近破坏处有明显减小;红砂岩限制性剪切蠕变破坏发育过程表现为先形成主控破裂面,又在其附近区域形成丰富微裂隙,并发育、相互贯通,最后克服剪切面摩擦力并发生突发式破坏,且伴有较大断裂声;其破坏模式发育过程呈渐进式,破坏模式呈突发式;建立了一种可以表征红砂岩剪切蠕变渐进式破坏发育过程的本构模型。     

Theoretical Analysis and Experimental Test of Full-scale Bamboo Scrimber Flexural Components

The bending tests and theoretical analysis of five full-scale bamboo scrimber components were conducted and the flexural behavior of bamboo scrimber was researched in detail. Results show that the typical failure modes of bamboo scrimber flexural components are the bamboo fiber fracture at the bottom and interlaminar shear failure near the neutral axis. The sectional stiffness control the design for the bamboo scrimber flexural components, the ratio of PL/250 of the load corresponding to the deflection limit value of L/250 and ultimate load Pmax has good stability. The relationship model of bending tensile strength fm and elastic modulus E was established by regression, which shows that the sectional stiffness expressed by the elastic modulus could predict the bearing capacity well. The plane-section assumption is still valid. The bamboo calculation methods of scrimber flexural components were proposed considering the materials properties of bamboo scrimber based on wood structure design methods. The design value of bamboo bending strength, shear strength parallel to grain and the elastic modulus E were presented preliminarily.     

Study on the Mechanism of Rockburst

Rockburst is often encountered in the underground engineerings of high geostress area, it is a kind of dynamic geodisaster.Depending on the examples of rockburst in the Erlang mountain highway tunnel and Jinping second powerstation tunnel, the fracture geometry shapes of rockburst are elaborated. Through the research of SEM analysis and rock mechanics tests of rockburst, three basic mechanics mechanisms of rockburst have been summarized,i.e., compression cracking, compression shear cracking,bending and breaking.     

Rockburst Hazard and Its Forcast and Treatments in Underground Engineering

Rockburst is a serious damage geologic hazard. According to the rockburst phenomenon in Erlangshan tunnel and the Jinping 2nd hydropower station and a large of rockburst data,this paper proposes that rockburst is a result that many factors synthesize. These factors include teconics ,epigenetic and superficial structure, wall-rock intensity, attitude of rocks, wall-rock state of stress, wall-rock deformation and underground engineering arrangement, etc. It is given that the mechanism of rockburst is a tension fracture damage under press.     

Kinetic mechanism of inorganic scale plugging removal atnear wellbore zone by high power ultrasonic technology

Based on the theory of solid and liquid coupling wave mechanics, the micro-dynamical characteristics caused by the transport of ultrasonic in porous media at near wellbore zone, including the elastic deformation of rock, the elastic crossflow of pore fluid and frame solid, and fluid squirt-flow produced by pore elastic deformation, are analyzed. Analysis of kinetics of peristaltic difference of porosity radius in porous media is presented. The characteristics of the removal of inorganic scale particle in porous media by using ultrasonic technology are also studied. Besides, by applying high power ultrasonic technology, the acoustic energy gathering in porous media at near wellbore zone leading to fracture of part rocks is illustrated. According to these analyses, the micro-dynamical mechanisms, such as inorganic scale fragmentation, ultrasonic cavitations, ultrasonic friction, ultrasonic peristaltic transport and ultrasonic fracture-making, occurred in inorganic scale plugging removal by high power ultrasonic technology are proposed.     

Experimental Analysis of Shear Performance of Wet-bonding Interface between FRP Plate and Concrete

By adopting seven kinds of adhesive resins, the mechanical properties of the interface between pultruded Basalt fiber reinforced polymer plates and cast-in-place concrete is studied according to two groups of stretching double-shear test. And it is compared with the dry-bonding interface between BFRP plates and the precast concrete. Further study is conducted by comparing the damage features, load-displacement curves, effective bond length, bond slip relationship and interface fracture energy between the two interfaces. It is found that the effective bond length of the two interfaces are similar, but the bond strength of the wet-bonding is about half of the dry-bonding. Finally, the shear stress-slip model is proposed for the wet-bonding interface based on the experimental data.     

Neural Network Model for Predicting the Transformation Tendency of the Stress on the Surrounding Rocks of Tunnel

The stress on the surrounding rocks affects severely the stability of tunnel. To estimate the stability of tunnel needs the transformation tendency of the stress on the surrounding rocks. After the transformation tendency of the stress on the surrounding rocks and the factors affected it are analyzed, the neural network model for predicting the stress on the surrounding rocks is created. The model is applied successfully to predict the change of the stress of the Guanyingyan tunnel in the Qiwan expressway, which proves that it is feasible to predict the stress on the surrounding rocks with the neural network model. The method is convenient and correct.     

Dynamic Prediction Analysis of Surrounding Rocks Stability for Non-symmetric Double-Arch Highway Tunnel

During the construction of non-symmetric double-arch rock highway tunnel, the complicated geological condition may affect the safety of the constructor and the engineering quality. In this paper, two treatment methods are put forward. At first, the site monitoring of surrounding rock displacement must be carried out, then, BP neural network is applied in predicting the displacement of surrounding rock based on the learning sample of measured value, so the stability of surrounding rocks may be analyzed and forecasted. During the analysis of BP neural network, the effects of joint and fracture of surrounding rock on displacement can be comprehensively considered, comparing the predicted values of displacement with those by FEM. The results show that not only the predicted error of BP neural network is relative small, but the predicted values of surrounding rock displacement are close to measured ones. So, the predicted values of BP neural network are reliable and may guide the engineering construction in site.     

Experimental Study on Shear Strength of High Strength Concrete Columns

On basis of the experiment on sixteen high strength concrete columns, their shear behaviors are analysed. The effects of shear-span ratio and axial compression ratio on failure behavior, cracking shear and shear strength are analysed. The authors have discussed the suitability of the design equations for shear strength in the code. This experimental study on shear strength of high strength concrete frame columns is the first one in this field at home and the results can be served as reference for the code of high strength concrete design.     

GFRP肋式剪力连接件受力性能对比试验研究

剪力连接件是保证GFRP混凝土组合梁/板中两种不同材料共同工作的重要构造,设计了矩形肋和T形肋两类GFRP肋式剪力连接件,进行了3组共8个GFRP肋式剪力连接件的推出试验,包括：矩形肋开孔、T形肋开孔、T形肋不开孔3组GFRP肋式剪力连接件,得到了其破坏形态、极限承载力、荷载滑移曲线及荷载应变变化规律,重点研究肋内开孔及肋的截面形式对GFRP肋式剪力连接件受力性能的影响。试验结果表明：GFRP肋式剪力连接件的破坏形态均为混凝土劈裂破坏;对比矩形肋开孔试件,T形肋开孔试件强度高、延性好;对比T形肋不开孔试件,T形肋开孔试件强度与延性均能提高。基于试验结果,建立了考虑肋内开孔及肋截面形式影响的GFRP肋式剪力连接件极限承载力计算公式,拟合得到了GFRP肋式剪力连接件的荷载滑移曲线上升段的理论模型,建立了其抗剪刚度计算公式。     

The Seismic Shear Capacity of I-Shaped and T-Shaped Reinforced Concrete Structural Walls

There are numerous shear walls with flanges in the high-rise buildings in P.R.China.The shear strength formula for shear walls in Chinese design codes lacks experimental data,while test results in other nations lack aseismatic shear strength test results for shear walls with flanges under axial force.In this paper,we report low-cyclic reverse load test results of shear wall models with large dimensions,one shear wall having an I-shaped cross-section and two with a T-shaped cross-section.We discuss why the aseismatic shear walls of high-rise buildings with large height-to-length ratios have small shear span ratios.We assess the reliability of the shear strength formulary in the Chinese codes for design of shear wall using the international shear wall test results.     

Mechanical properties and numerical simulation of unloading of brittle rocks under high geostress

The investigations on the deformation mechanisms, estimation of stability and technique of disasters controlled of brittle rocks excavated under high geostress are difficult points for rock mechanics and engineering geology. The evolutionary rule of mechanical parameters and deformation failure of brittle rocks are discussed based on unloading under high geostress, and the obvious characteristics of strain strength for brittle rocks under high geostress is found. It is presented that the brittle rock yielded follows Griffith rule of strain strength at peak. The elasto brittle plastic numerical calculation method is established considering the dynamical variation of mechanical parameters in course of unloading yield, and it is validated by practical engineering.