Mechanical properties of frozen rock mass with two diagonal intersected fractures

Based on previous research results, this paper investigated the influence of fracture morphology on mechanical properties and failure modes of rock mass with two diagonal intersected fractures. This study carried out a series of triaxial compression tests on rock-like specimens with two crossed fractures under negative temperature, concluded the following conclusions. The strength and failure modes of rock mass are significantly influenced by the dips of two crossed fractures. The strength of rock mass with two fractures cannot simply be estimated using the method that was developed for the rock mass with a single fracture. When the intersecting angle is less than 30°, the failure plane initiates at the tip of ‘‘artificial ruptures" and extends to the upper and lower ends of the specimen. In case of a higher dip and intersecting angle ranging from 30° to 60°, the failure plane propagates along one of these two fractures. The mechanical parameters of rock mass are not only related to the trace length, but also depend on the trace length ratio. One could roughly calculate the strength parameters using the approximation proposed in this paper. For the rock mass with a trace length ratio <0.3(short trace length/long trace length), the failure mode is dependent on the fracture with a longer trace length. When the trace length becomes significant and the trace length ratio approximates to 1, the failure plane propagates along two fractures, where an X-shaped failure pattern is presented. For the rock mass with moderate fractures and a trace length ratio of approximately 1, the failure mode is independent on fractures, which is similar to the damage pattern of intact rock. The strength and elastic modulus of rock mass decrease with the increase of spacing between fractures, while Poisson's ratio is independent on the spacing. The failure mode can be determined by the area of triangle created by two fractures. Damage occurs at the smaller triangle area first,and propagates with the two sides of the larger triangle.

Ground motion amplification pattern with TBM tunnels crossing soil-rock interface:Shaking table test

The current aseismic design has seldom considered the effect caused by underlain tunnels.Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation.This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests.Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions.The soil-rock site is classified as four micro-zones with varying conditions,to mount observation stations of acceleration sensors.Dynamic characteristics of the four zones are identified by the transfer function(TF)method,and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models.The test results indicate that the tunnel effect varies with the site conditions.Distinctively,a significant amplification effect is observed at the A4 zone,located on the soil deposit near the soil-rock interface.Then,it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification,revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.

A SURVEY ON THE PERIODIC SOLUTIONS TO KAPLAN-YORKE TYPE DELAY DIFFERENTIAL EQUATION-I

Since 1974,studying the original delay differential equation given by Kaplan and Yorke is about the problem on the existence of its periodic solutions,there have been a series of interesting and significant results in the previous literature.In this paper,we present a survey of some basic results.Some interesting open problems are also addressed.

A Markov-switching predator-prey model with Allee effect for preys

This paper concerns with a Markov-switching predator-prey model with Allee effect for preys.The conditions under which extinction of predator and prey populations occur have been established.Sufficient conditions are also given for persistence and global attractivity in mean.In addition,stability in the distribution of the system under con-sideration is derived under some assumptions.Finally,numerical simulations are carried out to illustrate theoretical results.