Experimental and numerical investigation of the Saint-Adelphe landslide after the 1988 Saguenay earthquake

On 25 November 1988, after the Saguenay earthquake, a landslide occurred in the municipality of Saint-Adelphe. The soil profile indicated that the deposit was composed of a stiff clay crustal layer overlying sensitive plastic clay with a soft-to-stiff consistency. A geotechnical investigation was carried out in situ and in the laboratory and included the use of a new seismic simulator to develop a geotechnical model of the Saint-Adelphe clay. The model was incorporated in a finite-difference slope stability analysis before and during the earthquake. The results showed the development of plastic zones and the generation of pore water pressure, but the global safety factor remained above unity. A post-seismic analysis that utilized a strain-softening behavior model showed the initiation and propagation of the plastic zone, as well as the development of a failure surface close to the observed failure surface. Therefore, it is proposed that the Saint-Adelphe landslide could be explained by a progressive failure mechanism.

Installation Time of an Initial Support for Tunnel Excavation upon the Safety Factors of Surrounding Rock

In engineering practice, the initial support system is commonly installed in the vicinity of the tunnel face after excavation, whereas the self-capacity of rock mass will fail to be utilized and the cost of the initial support system will be expensive. In this study, a methodology is proposed to determine the appropriate timing of initial support installation to find out the balance of tunnel safety and construction cost. Firstly, the global safety factor is introduced as the critical indicator to evaluate tunnel stability. Then, the comprehensive graphic relationship between the global safety factor and the distance to the tunnel face is established. Once the global safety factor decreases to an admissible value, the stability of the surrounding rock is in a critical state and the corresponding distance is the recommended location for installing the initial support. In these procedures, the installation time of the initial support at the typical tunnel section can be quickly designed and fed back by a direct indicator during construction. Meanwhile, several cases with different conditions have been carried out to discuss the regularity of the method.

Runout simulation of seismic landslides using discontinuous deformation analysis (DDA) with state-dependent shear strength model

The reliable numerical simulation of the landslide process contributes to the establishment of evidence-based disaster mitigation measures in seismically active zones. To achieve this goal, a simple and unified state-dependent shear strength model of discontinuities is presented to describe the shear strength degradation in a seismic landslide process. The proposed model establishes a relationship between the shear strength parameters and the global safety factor of the slope by assuming that the slope instability (or landslide initiation) is accompanied by an instantaneous shear strength degradation of discontinuities. To realize the model numerically, the algorithms for the computation of global safety factor and the modification of shear strength parameters were incorporated into the discontinuous deformation analysis (DDA). Subsequently, the kinematic accuracy of the improved DDA method was validated by comparisons with theoretical solutions for the dynamic sliding of a block on an inclined plane. Numerical simulations of the Daguangbao landslide triggered by the Wenchuan earthquake were performed using the improved DDA method. The results illustrate that the shear strength degradation of discontinuities affect the evolution process, travel distance, and post-failure shape of the seismic landslide significantly.

Safety parameters calibration in the structural design of sewer liners

The article concerns aspects of safety in the process of designing continuous polymer liners used to strengthen and seal sewers and drains. The issues of safety coefficients, the variability of basic loadbearing parameters of liners and the problem of sensitivity of analytical solutions describing load-bearing capacity are discussed. The currently used magnitude of safety factors has been verified. The results of an examination on the safety index of liners for strengthening sewers has been presented in the paper. The necessity for the verification of current concepts of liner safety normalisation was herein addressed. A postulation to abandon the analogy of liners for newly constructed pipes was formulated. Calculations using the Hasofer-Lind safety index (First Order Reliability Method) were performed in some cases. A verification and evaluation of the global safety factor for sewer liners were herein carried out.

Global Safety Factor or Nonlinear Design of Concrete Structures

The paper focuses on different approaches to the safety assessment of concrete structures designed using nonlinear analysis. The method based on the concept of partial factors recommended by Eurocodes, and methods proposed by M. Holicky, and by the author of this paper are presented, discussed and illustrated on a numerical example. Global safety analysis by M. Holicky needs estimation of the resistance coefficient of variation from the mean and characteristic values of resistance, and requires two separate nonlinear analyses. The reliability index value and the sensitivity factor for resistance should be also identified. In the method proposed in this paper, the resistance coefficient of variation necessary to calculate the characteristic value of resistance may be adopted from test results and the resultant partial factor for materials properties, and may be calculated according to Eurocodes. Thus, only one nonlinear analysis from mean values of reinforcing steel and concrete is required

Analysis for Drain Design of a Especial Rock Slopes under Rain Infiltration

The study is still few for the slopes of rock with low permeation，which has interfaces for rain infiltration and no interface for effusion. The stability of slope with rainfall infiltrating under different drain condition is evaluated by the global safety factor, based on the limited equilibrium methods. The following conclusions are obtained: (1) the two rows of drains don’t enhance the value of safety factor very much, and the layout of only one row of drains is advocated；(2) the effect of the system in which drains beat in marlite is better than the system in which drains beat in the breccia；(3) the effect of the system in which drains are designed in the toe of the slope is best, and the spacing of the drains whose diameter is 0.11 m should be less the 8m .