Shear Wedge Research Articles

Deflection and failure of high-stiffness cantilever retaining wall embedded in soft rock

In this study, a centrifuge modelling system has been developed, in which the loading process from design conditions to the ultimate failure conditions can be simulated on an embedded wall in soft rock at a constant centrifugal (50g) acceleration. Soft sand rock was artificially modelled by using a sand−cement−clay mixture. In-flight excavation and the lateral loading processes were simulated by means of draining water from the wall front and feeding water to the retained soil side, respectively. Two centrifuge model tests have been carried out to investigate the influence of embedment depth on the stability of large-stiffness cantilever walls having flexural rigidity equivalent to a 2·5 m steel tubular pile wall. The results observed reveal that the wall can stand in the design condition with relatively small embedment depth, and provides a reasonable safety margin against ultimate failure. The stiff cantilever walls move by rigid-body rotation about a pivot point under ultimate loads, and a small increment in the embedment depth – for example, 20% – can significantly increase the stability of the wall considered in this study. A compression failure of the embedded medium at the shallow wall front and a shear wedge failure at the wall back from the wall toe were observed.

Strength and fracture analysis of polymer-granular matter composites at variable weight percent ratio

In this study, the optimal weight percent ratio of resin and aggregate for a polymer-granular matter composite (PGMC) was determined in terms of its compressive strength. The PGMC was made with polyester for its resin, and white sand as its aggregate. The weight percent ratios of the PGMC varied as follows: 15:85, 20:80, and 25:75 for resin and aggregate respectively. The PGMC specimens underwent a compression test after a curing period of seven days at room temperature to determine its compression strength. Results indicate that the PGMC with weight percent ratio 25:75 had the highest average compression strength out of the three types at 76.4 MPa which is more than twice the strength of cement-based concrete. The 15:85 and 20:80 PGMCs yielded average compression strengths of 19.8 MPa and 60.8 MPa respectively. The most common fracture type for the PGMCs having weight percent ratios 20:80 and 25:75 was shear, occurring 83.3% of the time. On the other hand, the PGMC having weight percent ratio 15:85 displayed shear wedge fracture for five of the six trials.

Fracture mechanism of naturally cracked rock around an inverted U-shaped opening in a biaxial compression test

To determine the fracture mechanism of the hard and brittle surrounding rock containing natural cracks, a biaxial compression test was performed on a rhyolite, which was extracted from the deep buried Niba Mountain of the expressway in Sichuan Province, China. An inverted U-shaped opening was machined in the specimen to investigate the initiation, propagation and coalescence of cracks around the opening. The fracture modes, tangential strain and principal strain around the opening were monitored and discussed. According to the measured strains in different locations of surrounding rock, the floor was firstly tensile fractured and the roof followed. The “dumbbell-like” compressive strain concentration was found in the sidewall. However, the intense influence region of stress was limited in the shallow rock which was about 0.5r in this experiment, since the deep surrounding rock was in the state of slight compression and tension. Considering the fracture process, “V-shaped” shear wedge was formed to lead to shear slipping under the “dumbbell-like” compressive strain concentration in the sidewall. It indicated that the pre-existing natural cracks in the hard and brittle rock played an important role in consuming strain energy by initiating and propagating during biaxial compression. Slight fracture-induced damage, shear slipping in the sidewall, was occurred instead of common splitting and rockburst. On the basis of the experimental achievements, it was important to strengthen the shallow surrounding rock and prevent the hysteretic failure in the fractured sidewall of the inverted U-shaped opening.

A physical and numerical investigation of the failure mechanism of weak rocks surrounding tunnels

The large-scale construction of railway tunnels in China is hindered by several challenges, including large depths, large tunnel cross-sections, and fragile geological conditions. In this paper, we explored a new physical and numerical simulation method that improves upon the currently used methods to investigate the deformation and failure modes of weak rocks surrounding a tunnel. We also compared the results from physical tests and numerical simulations with the field measurements to demonstrate the effectiveness of the proposed numerical simulation method. In the physical model test, an artificial speckle field was developed by staining quartz sand particles and mixing the particles with barite powder and petroleum jelly in preset proportions. The artificial speckle field was employed in the digital speckle correlation method (DSCM) to monitor the evolution of the strain field on the surface of the plain strain model for tunneling during loading. A secondary strain-softening constitutive model using the numerical modeling code FLAC3D was developed (degradation constitutive model) by considering the deformation modulus degradation in the numerical simulation. The failure mode of weak rocks surrounding a tunnel in the physical model test was examined using the developed degradation constitutive model. Both the physical and numerical results revealed that the least stable area was the shear wedge along the minimum principal stress, which was confirmed in the damage zone of the surrounding rocks. The results were consistent with previous research findings. The results of the DSCM in the physical model test indicated that the shear wedge in the middle part of the tunnel and the cracks around the arch of the tunnel were induced by shear strain, whereas the collapse of the arch was attributed to a combination of tensile strain and shear strain. A comparison of the physical and numerical simulation results demonstrated that the degradation constitutive model can be used to describe the extent and depth of the excavation damage zone of tunneling. A comparison of the displacements from the numerical simulation and field measurements indicated that the degradation model can be used to capture the displacement of weak rocks surrounding tunnels.

Development of All-Wood Connections with Plywood Flitch Plate and Oak Pegs

This paper proposes a new method for beam-beam connections, which include plywood as slot-in plates connected by oak pegs. A total of 96 specimens were fabricated for tests to explore the minimum required end distances and spacing between pegs parallel to the grain. A new failure mode, termed shear wedge that is different from those found in previous research, was found. A spring model was also proposed in this study to investigate the stiffness of the connections, and feasibility of EC5 to be applied on the new proposed connections was also examined. The effective number was discussed in this study and modified in accordance to the experimental results. The result of this study shows the new connections proposed do not lead to brittle failure unless failure in plywood occurred.

Simplified analytical solution for free vibration characteristics of Hardfill dam

Formulas for computing natural frequencies and modes of Hardfill dams are derived based on onedimensional shear wedge theory, in which the influences of the upstream concrete face and hydrodynamic pressure of water on the dams’ natural frequencies and modes are discussed. Furthermore, the seismic responses of Hardfill dams are calculated using response spectrum method. An example is analyzed to compare the differences of natural frequencies and modes between shear wedge method and FEM. Then the applicability and accuracy of shear wedge method to analyze free vibration characteristics of Hardfill dams are proven.

Influence of Silanisation Parameters With γ-Methacryloxypropyltrimethoxysilane on Durability of Aluminium/Acrylic Adhesive Joints

Silane coupling agents have extensively been used as adhesion promoters in the GRP (Glass Reinforced Plastic) composites. In recent years, the application of silanes in aluminium bonding process has been extensively investigated. Silane surface treatment is a more environment-friendly alternative than other treatments, which use toxic chemicals (hexavalent chromium compounds, strong acids, etc.), such as FPL (Forest Products Laboratory) etch, CAA (chromic acid anodisation) or PAA (phosphoric acid anodisation). The aim of this work was to optimize the γ-methacryloxypropyltrimethoxysilane application process to obtain the best durability in toughened acrylic bonded aluminium joints. Variables such as pH, concentration of silane in aqueous solution, drying temperature and pretreatment prior to silanisation have been investigated. The durability was tested using single-lap shear specimens and wedge tests. Specimens were exposed to 95% RH at 50°C, for 90 days. Silanisation parameters such as solution concentration and drying temperature showed a great influence on the durability; however pH had only a little influence. Adherend surface preparation prior to silanisation was found to be a significant factor. The best bond durability performance was provided by the P2 etch and grit blasting, which performed better than the other pretreatments studied.

Slumping–rolling transition of granular solids in rotary kilns

Recent research work on the slumping–rolling transition of granular solids in rotary kilns is reviewed. A mathematical model is presented for the calculation of critical Froude number. It is supposed that the transition occurs when the time needed by the propagating avalanche to leave the shear wedge becomes comparable to the time of the shear wedge to be refilled with new particles transported by the rotating wall. It is found that the critical Froude number is proportional to the size ratio d / D (particle to cylinder diameter) and inversely proportional to sin 2 ε , where ε is the fill angle of the solid bed. Besides the particle diameter, the influence of the bed material needs to be described by only one measurable parameter—the upper angle of repose. To validate the model, the transition behaviour of different bed materials was measured in cylinders of three different sizes. The model is found to predict our measurements as well as those reported in the literature. It is also compared with models from other authors.

Nonlinear Hysteretic Dynamic Response of Soil Systems

A simplified analysis procedure for the nonlinear hysteretic dynamic response of soil or structural systems, or both, is presented. The method is based on a Galerkin formulation of the equations of motion in which the solution is expanded using basis functions defined over the spatial domain occupied by the soil system. The basis functions are selected as the normal eigenmodes of the linearized problem. The hysteretic stress-strain behavior is modeled by using elastoplastic constitutive equations based on multi-surface kinematic plasticity theory. Accuracy and versatility of the technique are demonstrated by applying it to analyze the nonlinear dynamic response of an earth dam. The dam is modeled as a one-dimensional hysteretic shear wedge. Parametric studies assessing the influence of the nonlinearities on the response are presented. Finally, comparisons are made with results obtained through a more elaborate finite element representation of the dam.

Estimation of the Fundamental Period of Large Earthfill and Rockfill Dams

A semi-empirical expression has been derived for the fundamental period of large earthfill and rockfill dams. Derivation is based on analytical solutions and has been calibrated using the empirical data available. Analytical solution involves a heterogeneous shear wedge with a realistic distribution of small-strain shear modulus. The effect of the “third dimension” has also been taken into account by making use of two and three dimensional finite element and shear wedge solutions, and a simple expression has been derived by the aid of a single degree of freedom idealization. Empirical data come from forced vibration tests and response observations during small earthquakes. Recently the fundamental period of a large rockfill dam became available which had not been used in the development of the period expression presented. The accurate prediction of the period of this dam has shown that the equation will be useful in practice for estimation of the small strain fundamental periods of large dams.

Earthquake Response of Earth Dams

The widely used shear wedge approach for earthquake analysis of earth dams is compared with a two-dimensional dynamic stress analysis technique which uses the finite element concept. Natural frequencies and mode shapes of typical earth dam cross sections as well as their responses to the El Centro earthquake of 1940, as obtained by the two methods, form the basis for the comparison. The results presented demonstrate that a two-dimensional analysis is necessary to satisfactorily determine the earthquake response of an earth dam cross section.

Launching ultrasonic shear waves into solids at normal incidence by pressure coupling

The launching of ultrasonic shear waves generated by a crystal transducer into a solid medium is discussed, and the method whereby the transverse oscillations are coupled from the transducer to the medium by the application of a steady mechanical pressure is more particularly examined. The mechanical design of a single-crystal transducer, and of a four-crystal transducer which enables perpendicular planes of polarization to be readily selected, is discussed, together with methods of applying the steady pressure (which is typically about 20,000 lb/in 2). The design of a shear wedge which permits the axis of polarization of a transducer to be readily determined is also given.