The Effect of Targeted Field Investigation on the Reliability of Earth-Retaining Structures in Active State

Abstract

This paper introduces the concept of targeted field investigation on the reliability of earth-retaining structures in an active state, which is implemented in a random finite element method (RFEM) framework. The open source RFEM software REARTH2D was used and modified suitably in order to accommodate the purposes of the present research. Soil properties are modeled as random fields, and measurements are modeled by sampling from different points of the field domain. Failure is considered to have occurred when the “actual” resultant earth pressure force on the retaining wall (calculated using the friction angle random field) is greater than the respective “predicted” force (calculated using an homogenous friction angle field characterized by the mean of the values sampled from the respective random field). Two sampling strategies are investigated, namely, sampling from a single point and sampling from a domain, through an extensive parametric analysis. As shown, the statistical uncertainty related to soil properties may be significant and can only be minimized by performing targeted field investigation. Among the main findings is that the optimal sampling location in the active state is immediately adjacent to the wall face. In addition, it is advisable that the entire wall height be considered in sampling. Finally, it was observed that the benefit from a targeted field investigation is much greater as compared to the benefit gained using characteristic values in a Load and Resistance Factor Design framework.

The Effect of Targeted Field Investigation on the Reliability of Earth-Retaining Structures in Passive State: A Random Field Approach

“…Because the present analysis deals with small differences in p f values, the number of realizations was set to 3000 for obtaining stable results (see Appendix A in the present paper). The element size was chosen to be half of the smallest scale of fluctuation considered in this study (see [6,23]).…”

“…While Eurocode 7 uses characteristic values (cautious estimate of the mean of a set of values) so as to take account of the inherent variability of the soil, the various North America codes [4,[30][31][32] use mean values for soil properties. The following statistical equation using 95% confidence level is often adopted in practice for the calculation of the characteristic value [6,13,29,33]:…”

“…Statistical uncertainty is related to limited soil testing, i.e., to the fact that the soil mass, which is affected, is much greater in volume than the soil mass tested in the field or in the lab. Regarding statistical uncertainty, it is worth mentioning that current design codes (e.g., AASHTO [4] or EN 1997-2:2007 [5]) give some general recommendations (see also Appendix A in [6]) related to the extent of the subsurface exploration and aiming at identifying possible unfavorable geological conditions.…”

“…Based on four sampling locations, they drew the conclusion that a single sampling point located at an offset distance equal to approximately one wall height from the wall results to lower probability of failure and that this probability is reduced when additional sampling points are considered. Finally, in one of their recent works, the authors [6] examined the effect of targeted field investigation on reducing statistical uncertainty in active state analysis of earth retaining structures. The parametric analysis in question, involving 2165 different cases for each of the sliding and overturning modes of failure, indicates that the optimal sampling location is at zero distance from the wall, while the sampling domain length should preferably be equal to the wall height.…”

Reducing Statistical Uncertainty in Elastic Settlement Analysis of Shallow Foundations Relying on Targeted Field Investigation: A Random Field Approach

“…They found that there is an optimal number of site investigation tests, beyond which the cost of additional boreholes does not justify the cost savings due to reduced slope failure risk. Finally, the authors [12] studied the effect of targeted field investigation on the reliability of earth retaining structures in the active state by working with the Random Finite Element Method. This extensive parametric analysis involving 2165 different cases (for each mode of failure, i.e., sliding and translational) showed that the optimal horizontal sampling location in the active state is adjacent to the wall face, whilst the optimal sampling domain length is equal to the wall height.…”