Estimating the Basal Heave Stability of Narrow Braced Excavations

Engineering practices indicate that narrow braced excavation exhibits a clear size effect. However, the slip circle method in the design codes fails to consider the effect of excavation width on basal heave stability, causing waste for narrow excavation. In this paper, numerical simulation for basal heave failure of excavation with different widths was performed by FEM with SSRT (shear strength reduction technique). The results revealed that the failure mechanism of narrow excavation is different from the complete slip circle mode. In addition, the safety factor decreases increasingly slowly as the excavation widens and stabilizes when approaching the critical width. Subsequently, the corresponding computation model was presented, and an improved SCM (slip circle method) was further developed. Finally, the engineering case illustrated that it can effectively optimize the design, which exhibits clear superiority.

Stability and Countermeasures for a Deposit Slope with Artificial Scarp: Numerical Analysis and Field Monitoring

This paper presents the results of the stability analysis of a deposit slope with an artificial scarp in a tunnel exit and an evaluation of the effectiveness of four proposed reinforcement schemes. A typical slope section was used to study the deposit slope stability and retaining mechanisms of the reinforcement systems. A series of two-dimensional (2D) finite element models (FEM), combined with a strength reduction technique, was established using the Phase2 software. According to field monitoring results, the horizontal displacements of the front, middle, and rear of the slope decreased gradually, and the safety factor increased successively. The front of the deposit slope was in a state of limit equilibrium as a result of the artificial scarp formed by long-term manual excavation. Anchors and concrete frame beams provided stress compensation and improve the stability of the deposit slope, and front prestressed anchor cables and stability piles strengthened the mechanical properties of the rock and soil masses and provided resistance at the front of the deposit. Rear stability piles prevented the front of the deposit from being pushed and the middle and rear of the deposit from being pulled and provided resistance at the front of the deposit. The field monitoring also showed that the deformation of the deposit slope was effectively controlled. The study results provide insights into the effectiveness of measures for reinforcing and maintaining the stability of deposit slope with artificial scarps.

Stability Charts for Pseudostatic Stability Analysis of Rock Slopes Using the Nonlinear Hoek–Brown Strength Reduction Technique

This paper presents a set of stability charts for the stability assessment of rock slopes that satisfy the Hoek–Brown (HB) criterion under various seismic loading conditions. The nonlinear Hoek–Brown strength reduction technique is used to conduct pseudostatic stability analysis of rock slopes subjected to horizontal seismic excitation. Based on an extensive parametric study, first, a set of stability charts with a slope angle of β = 45° under static and pseudostatic conditions are proposed by using ABAQUS 6.10 software. Second, the slope angle weighting factor (fβ) and the seismic weighting factor (fkh) are adopted to characterize the influence of slope angle (β) and horizontal seismic acceleration coefficient (kh) on the rock slope stability. Finally, the reliability of the proposed charts was validated by three typical examples and two case studies, and the results show that the values of the factor of safety (FOS) obtained from the proposed charts are consistent with the values from other methods. The proposed charts provide an efficient and convenient way to determine the FOS of rock slopes directly from the rock mass properties (γ and σci), the HB parameters (mi and GSI), the slope geometry (H and β), and the horizontal seismic coefficients (kh).

Stability Analysis of a Slurry Trench in Cohesive-Frictional Soils

The slurry trench has become increasingly common in underground engineering and the stability of a slurry trench has been an important design issue. Although many studies have focused on the overall stability of a slurry trench, few of that are related to its local stability. Based on the limit analysis, both two dimensional and three dimensional rotational failure mechanisms for the local failure of a slurry trench in a sandwiched weak layer are proposed, and the upper solutions of 2D and 3D safety factors for local failure mechanisms are derived to evaluate the stability of a slurry trench. Moreover, a numerical analysis combined with the strength reduction technique is performed to investigate the local stability and the local failure process of a slurry trench. The proposed analytical method is verified through the comparison with the results of FLAC3D. Finally, a parametric study on the influences of geometric and geologic parameters on the local stability of the slurry trench are investigated. The results show that the investigation on the local stability of a slurry trench is effective and reasonable, which can provide a reference for the engineers in the practical engineering.