Spaces for backfills are often constrained and limited to a narrow width when retaining walls must be built close to existing stable walls in urban areas or near rock faces in mountainous areas. Estimation of lateral earth pressure acting on the back of the retaining wall has been typically based on classical earth-pressure theories such as Coulomb’s theory or Rankine’s theory, which assumes that the backfill is sufficiently wide to allow the full development of failure planes in the backfill. It has been generally recognized that the classical earth-pressure theories tend to significantly overestimate the lateral pressures for retaining walls with narrow backfill width. However, data from experimental studies are scarce, preventing a close examination of how narrow backfill spaces and various wall movement modes impact the forming of the failure surfaces and the distribution of lateral pressure acting on the retaining wall. In this study, a rigid retaining wall model was custom designed and built to investigate the effects of narrow backfill spaces on lateral pressures and backfill failure under active earth-pressure conditions. A series of tests was conducted on combinations of different backfill widths and wall movement modes [translation (T) mode, rotation about bottom (RB) mode, and rotation about top (RT) mode]. The failure surfaces in the backfill and distribution of lateral pressures acting on the back of the wall were recorded for each of the tests. Results of the tests demonstrated that the failure surfaces were continuous and nonlinear and limited by the width of narrow backfills. It was also found that the mode of retaining wall movement plays a role in forming the failure surfaces and mobilizing the lateral pressures. The coefficient of active pressure K_a based on measured lateral pressure decreases along with the depth. Whereas the RT mode showed much higher K_a values at the upper part of the wall, K_a values for the T mode and RB mode were smaller than those found by Coulomb’s theory. The resultant of lateral pressure for all three wall movement modes was significantly smaller than that of Coulomb’s solution, with its point of application generally higher than one-third from the wall base. A simple and practically useful analytical solution of the lateral pressure based on arching theory is presented in this article and shows a reasonably good agreement with the measured lateral pressure for the translation and rotation about the bottom modes of retaining wall movements.

This study attempts to identify mechanical and physical properties of geogrids that are critical to their effectiveness in the stabilisation of pavement subgrade. Geogrid properties, including aperture size, wide-width tensile strength and junction strength, for four geogrid products are correlated with bench-scale interface test results, including direct shear and pull-out, and accelerated pavement testing (APT) results. APT is conducted through the use of a one-third scale APT device, the model mobile load simulator (MMLS3) on geogrid-reinforced pavement sections. The pavement sections are constructed on a subgrade soil with a low California bearing ratio. The performance of each pavement section is evaluated by measuring surface rutting at various trafficking stages. The analysis reveals a strong relationship between performance and junction and tensile strength of geogrids at small strains, whereas aperture size has a positive correlation with pull-out test results.

Despite the fact that the adverse health effects due to the intake of lead have been well studied and widely recognized, lead contamination in drinking water has been reoccurring worldwide, with some incidents escalating into a public drinking water crisis. As lead contamination is often related to lead-based pipes close to or inside homes, it is not realistic, at least in the near term, to remove and replace all lead connection pipes and lead-based plumbing. Effective monitoring of lead concentration at consumers’ water taps remains critical for providing consumers with first-hand information and preventing potential wide-spread lead contamination in drinking water. This review paper examines the existing common technologies for laboratory testing and on-site measuring of lead concentrations. As the conventional analytical techniques for lead detection require using expensive instruments, as well as a high time for sample preparation and a skilled operator, an emphasis is placed on reviewing ion-selective electrode (ISE) technology due to its superior performance, low cost, ease of use, and its promising potential to be miniaturized and integrated into standalone sensing units. In a holistic way, this paper reviews and discusses the background, different types of ISEs are reviewed and discussed, namely liquid-contact ISEs and solid-contact ISEs. Along with the potential opportunities for further research, the limitations and unique challenges of ISEs for lead detection are also discussed in detail.

A slip-failure surface forms in the backfill soil upon sufficient yielding or movement of the wall that retains the backfill soil. The shape of the slip-failure surface plays an important role in estimating the lateral earth pressure, including its magnitude and location of its resultant force. As retaining walls at times must be built with narrow and constrained backfill space, this study presents an analytic derivation of the slip-surface shape in narrow cohesionless soil behind a rigid retaining wall under translation movement mode of the wall. Results of a series of experimental tests were presented to demonstrate the effects of narrow backfill spaces on forming the slip surface and that the slip surfaces are curvilinear planes developed from the heel of the retaining wall to the crest of the backfill. Based on the experimental findings, a rigorous analytic derivation using a variational limit equilibrium method is conducted to determine the governing equation for the shape of the slip surface in the narrow backfill soil. The analysis reveals that the active failure plane of the narrow soil behind a rigid retaining wall agrees well with a logarithmic spiral plane. The derived log-spiral slip-surface plane is further verified by experimentally observed slip surface and measured active lateral earth pressure. Substantial discrepancy was observed in the lateral earth pressure distribution between the logarithmic spiral slip surface and the assumed linear planar slip surface, indicating that the assumption of a linear planar slip surface in narrow backfill may result in significantly erroneous estimation and lead to an overly conservative and uneconomical design. Furthermore, a threshold value of 0.5 is identified for the backfill width/height ratio that distinguishes the narrow backfill from a sufficiently wide backfill.