Probabilistic and Geotechnical Modeling of an Excavation in the Outskirts of Qaen

Summary
An excavation operation for the building purposes is a high-risk activity, which is done for different reasons, such as achieving an appropriate level of the earth for foundation or construction of basements. In this paper, using the Slide 6.0 program the stability of a pit wall in the outskirts of Qaen is investigated at first and then the pit wall stability after using soil nailing with various patterns is analyzed. Using back analysis, sensitivity analysis, and probabilistic analysis, this study presents a comprehensive model for analyzing pit walls, and will be useful for excavation operation in neighboring areas as well. Finally, several pit designs with acceptable safety factors have been proposed for pit excavation.
 
Introduction
Due to the growing trend of urban populations, the construction activities are increasing in central and marginal areas of cities. One of the basic concerns in these constructions is the stability of the excavated pit wall. The basic rule of judgment about the stability of a pit wall is the standard safety factor. In the traditional deterministic approach of safety factor calculation, any error or uncertainty in the soil parameters is directly reflected in the results. In recent years, the use of the probabilistic approach that provides additional measures related to the probability of failure and risk rate has become popular. In the probabilistic approach in addition to the mean safety factor, the probability of failure and reliability index are also obtained.
 
Methodology and Approaches
To perform a probabilistic analysis of a pit wall, strength properties of the soil layer and the soil density were defined as variable inputs. The coefficients of variation of these parameters according to laboratory experiments were selected. Normal and log-normal statistical distributions were used for the input variable parameters as recommended by USACE. For the efficient performance of the probabilistic analysis, Monte Carlo simulation was used. This way, and using the Slide 6.0 program, the stability of a pit wall in the outskirts of Qaen is investigated with various patterns of soil nailing as the supporting system.
 
Results and Conclusions
According to the results of this study, the soil is unstable for excavation operation and employing soil nailing technique and reducing the pit wall slope angle are appropriate steps to achieve a secure condition. Several safe pit designs have been proposed for excavating the pit.