Papers by Author: Yu Yong Jiao

Abstract: In this paper, the mechanical behavior of excavation and support construction of Weishe tunnel, which is a section of the Yangwu expressway, is studied quantitatively using 3D finite difference numerical simulation method. A sequential excavation method is used and the results show that the vault settlement occurs mainly on the phase of upper bench excavation. The convergences of upper and lower sidewalls occur mainly on the phase of lower bench excavation. During the construction, the surrounding rock pressure in the vault and sidewall of the tunnel decrease. Axial force of anchor reaches the maximum value after the finish of second lining. However, the surrounding rock pressure and internal force of steel arch reach the maximum value after completing the upper bench excavation, and then become as smaller as half of the peak value during the lower bench excavation.

Abstract: This study is to present a numerical investigation on fragmentation and perforation of concrete slab by hard projectile using discrete particle approaches. Discrete Element Method (DEM) and Discontinuous Deformation Analysis (DDA), the two representative discrete particle approaches, are employed to simulate a normal perforation of concrete slab by a hard ogival-nose shaped projectile, and the phenomena of spalling, plugging and scabbing are reproduced.

Abstract: There are a large number of cracks, joints and layers with different scales and orientations in the rock masses. With the structural formation in it, the rock mass is unlike the isotropic and homogenous materials in physics and mechanics characteristics, and the failure of the rock mass is controlled by those discontinuities. This paper studies the stability of a jointed rock slope with bedding-planes. Universal Distinct Element Code (UDEC) is used to carry out the numerical analysis. The factor of safety (FOS) and failure mode are obtained by strength reduction technique before and after the steel bolts are installed in the slope. In addition, the forces along the bolts indicate that they reaches the maximum value in the potential slip surface of the slope.

Abstract: The instability of the roadway is a general problem for most of the deep mine roadways due to high geo-stress and large deformation, which require that the more reasonable and effective support measures are designed and employed. By applying the 3-D explicit finite difference software FLAC3D, this paper establishes the numerical calculation model of a roadway located in about 700m depth based on the geologic condition of the site which the roadway is in as well as the results of the in-situ stress measurement and the laboratory tests for the physical-mechanical properties of rock. Furthermore, three different support scenarios are raised and the optimum one is determined by calculating and analyzing the distribution of the plastic zone and displacement field in the rock surrounding the roadway with the above three scenarios.

Abstract: In the construction of railways in western part of China, more and more long tunnels have been excavated these years, and several ones are under construction at the moment. Because of the complex geologies like faults, fractured zones, karst cavities as well as water bearing formations, the stability and safety of tunnels have been challenging topics in the construction process. In this regard, the advance knowledge of the location, size, and spatial information of the uncertainties ahead of the face is very important to the contractors. In this paper, by using the Tunneling Seismic Prediction (TSP) technique, site experiments are performed to predict hazardous formations ahead of face in a railway tunnel. Through interpretation of the testing data, the wave velocities and the mechanical parameters of the surrounding rock are obtained, and the faults/fractures are recognized. The study shows that compared to time-consuming core drilling method, the wave reflection based TSP method can predict major uncertain formations in long range ahead of the face in short time. The downtime, as we know, is one of the key factors in speeding the tunnel construction. For the prediction accuracy, the TSP technique is able to provide enough information due to its multiple proof-test procedure.

Abstract: In the classical Coulomb’s earth pressure theory, the failure surface in the backfilled clay behind rigid retaining wall in slope engineering is assumed a plane. However, it has been proved by a number of laboratory and field tests that this failure surface is actually a curving surface. In this paper, based on the vertical differential element method and the variational principle, a new analytic solution to determine the actual failure surface in the backfilled clay is derived, and the effects of the backfilled clay’s properties as well as the effects of the retaining wall’s smoothness are discussed. The result obtained from the proposed approach is compared with Coulomb’s earth pressure theory.

Abstract: There are several different yield surfaces of Drucker-Prager yield criterion which corresponds to Mohr-Coulomb yield criterion in principal stress space. The different yield surfaces are determined by parameters in Drucker-Prager criterion. The influence of the different parameters on computational results is discussed in the paper, and the use of the equivalent Drucker-Prager criterion to Mohr-Coulomb criterion is suggested when elastoplastic analysis is performed in engineering problems.

Abstract: This paper presents a three-dimensional numerical model for simulation of blocky rock structures based on static relaxation approach. The proposed method utilizes static equilibrium equations to calculate the displacements of blocks, compared to Newton’s second law applied by the traditional DEM. In order to obtain displacements simultaneously, the technique of global stiffness matrix is introduced in to form the global equilibrium equations. Because large displacements come from the accumulation of small displacement increments, an iteration procedure is adopted in the calculation. A C++ program is developed based on the proposed algorithm, and an illustrative example is computed for verification.

Abstract: A numerical technique based on using manifold elements in finite element method, for modeling propagation of arbitrary cracks in solids, is described. When the region with crack(s)is subjected to external loading and the crack(s) starts to extend, the crack growth may intersect boundaries of nearby finite elements. Those intersected finite elements are replaced by manifold elements. The technique, by which the initial finite element mesh can be kept unchanged during the processes of crack propagation, is called manifold elements in finite element method. The crack growth is governed by the theories of linear elastic fracture mechanics. The stress intensity factors are computed by a contour integral technique and crack trajectory is determined by applying the maximum tangential stress criterion. Finally, test examples are given to verify the new method and the predicted trajectories are compared to experimentally obtained crack growth paths with good agreements

Abstract: By using the real-time CT (computerized tomography) unit with specially developed water-injection loading apparatus, several failure tests of single-crack concrete specimens with interstitial water pressures under triaxial compression were conducted. The complete failure process: the closure, the initiation of new damage area, the secondary closure, as well as the crack propagation of the specimens were simulated. The CT images at each stage, the CT numbers and the comparison among different sections in the specimens were obtained. Based on the observed results, the role of compressive pressure in damage and propagation of hydrous crack can be intuitively revealed, and the characteristics of damage-evolution of cracks in brittle material can be better understood at meso-level.