Vincent Z. Wang

Vertical Stress Determination within Backfilled Mine Stopes

AbstractDetermining the vertical stresses within underground mine stopes is necessary for designing the barricades that block the drives during filling. This paper discusses two different procedures that can be used for determining the vertical stress profile, which give different values of stresses. The difference is attributed to fixing the bottom of the stope, implying zero displacement in any direction. The reasons are discussed, and it is suggested that the method commonly used in numerical modeling (Method 2) is not necessarily the better of the two. The alternate method (Method 1) models the field situation better when the loadings at the bottom during filling are required, mimics the laboratory model tests, and gives the same stress profile for all stopes with any aspect ratio. The findings are applicable to backfilled trenches as well.

Seismic fragility evaluation with incomplete structural appraisal data: an iterative statistical approach

AbstractThis paper presents an iterative statistical approach to evaluating seismic structural safety using incomplete appraisal data. Despite the continuous improvement to traditional structural assessment procedures and the recent progress in structural health monitoring methodologies, practically acquired structural appraisal data may often be incomplete. The occurrence of the appraisal data missingness could be ascribed to the malfunction of data acquisition systems, the abnormality during data transfer, and the inaccessibility of critical quantities, among other reasons. The study begins with a quantitative investigation into the sensitivity of the seismic fragility evaluation with respect to the structural appraisal data missingness through the defined additional information loss and probability of noninformativeness. Subsequently, a remedy for the missingness of the structural appraisal data, instead of a precaution against it, is formulated by employing the expectation-maximization (EM) algorithm....

Laboratory investigations of arching in backfilled mine stopes

Mine backfilling is an effective way of disposing of the tailings, and it improves the regional stability, allowing nearby regions to be mined. The backfilled underground voids can be approximated as rectangular prisms with base dimensions of 20-60 m and heights as much as 200 m. A series of laboratory tests were carried out in model stopes with square and rectangular cross sections, having height to width ratio of six. The stopes were instrumented to measure the fill load transferred to the base of the stope as well as the remainder that was transferred to the wall. The laboratory model test results are compared with those from analytical closed-form solutions and numerical modelling work carried out using FLAC3D, and the agreement among the three different approaches is excellent. The findings reported herein will shed some light on the understanding of the stresses within minefill stopes, and improve the design practice and the current state-of-the-art.

An Expectation-Maximization Algorithm Embedded Framework for Safety Assessment of Reinforced Concrete Systems

This paper studies the safety assessment of in-service reinforced concrete (RC) structures with incomplete appraisal data. An appraisal data missingness event may occur under a series of circumstances, such as the breakdown of the data acquisition system involved. To deal with the incomplete appraisal data, two straightforward options—that is, pairwise and listwise parameter estimation schemes—are first explored, and the discussion focuses on the positive-semidefiniteness criterion, the additional information loss, and the probability of noninformativeness. An expectation-maximization (EM) algorithm embedded safety assessment framework for in-service RC systems is then formulated as a remedy for the missingness of the appraisal data. Through a designed statistical hypothesis testing scheme, the efficacy and the general applicability of the framework are illustrated using both the numerically simulated appraisal data and the data collected by a rebound hammer during a field investigation. The proposed framework has the potential to be incorporated into the sustainable RC structural design paradigms.

Towards the reliability quantification of recyclable precast concrete elements and sub-assemblies: A feasibility exploration of the application of an expectation-maximization algorithm embedded safety assessment technique

Documenting a preliminary pilot study of the quantification of the reliability of recyclable elements and sub-assemblies in a precast concrete structure, this paper explores the feasibility of applying a most recently developed expectation-maximization (EM) algorithm embedded safety assessment technique. The recent push to increase sustainable practices in the construction industry can be attended to by introducing the repurposing of concrete elements and sub-assemblies in new structures. Precast concrete provides one of the best options to undertake this task due to its superior cost effectiveness, access to detailed plans, and quality control during pouring. To ensure the intended recycled precast concrete elements and sub-assemblies are safe to use, a structural appraisal must be carried out, yet it is not uncommon that some data missingness is encountered during such tests. The feasibility of addressing this issue by resorting to an EM algorithm embedded technique is investigated in this study. It is illustrated that the difference in the probability of failure between the relevant complete- and incomplete-data scenarios is not statistically significant. This paper outlines the application of the EM algorithm embedded technique in the field of precast concrete structures to enact a potentially vital sustainability initiative.

Time-invariant and time-variant reliability analyses of reinforced concrete systems with appraisal data missingness

This paper deals with reliability analyses of in-service reinforced concrete (RC) systems with the missingness of some structural appraisal data. After succinctly illustrating the appraisal data missingness, both the time-invariant and time-variant reliability analyses are performed based on the expectation-maximization (EM) algorithm with access to only incomplete structural appraisal data. Specifically, the time-invariant analyses allow for the combination of dead and live load effects, as well as their magnitudes; while in the time-variant analyses, hazardous loading with different values of the occurrence rate and the degradation of the resistance of an RC system with time are considered. The performance function of an RC system is configured such that it may appositely take into account the existent safety redundancy in the system. With a nonparametric statistical inference technique, simulated and field-collected structural appraisal data are then used to demonstrate the effectiveness of the formulated framework for the reliability analyses.