Cement stabilization is a well-established technique involving the addition of cement to increase shear strength of soft soils. Studies on the prediction of cement-treated slurry clay generally do not cover a comprehensive suite of experiments to develop a more in-depth strength-development model, and applicability is often limited to their specific database. This paper presents a large database of unconfined compressive strength tests of cement-treated marine clay over a wide range of mix ratios and curing ages. An improved predictive strength-development model is proposed that considers the effect of mix proportions and curing duration. The actual and predicted strength values are found to agree with a correlation coefficient of 0.997. The model is also shown to be applicable to several clay and cement types; the good fit to experimental data is indicated by correlation coefficients exceeding 0.95, which is superior to existing classic prediction models.

This study presents a closed-form solution for kinematic stability of a two-stage slope with a strip footing placed near the slope crest of the layered soil strata. According to the upper-bound theorem of plasticity theory, the normalized ultimate bearing capacity and yield seismic coefficient that the slope could withstand without failure under the limit state are derived on the basis of the pseudostatic approach. In addition, under specific parameters, the least upper-bound solutions can be calculated with the use of optimization. The stability factors were compared with those in existing literature under static, seismic, and undrained conditions to validate the proposed approach and the analytical solutions. A thorough parametric study involving parameters, such as soil cohesion and self-weight, nonhomogeneous coefficients, and external conditions (including the magnitude and position of strip footing and seismic effect), was carried out in this study. The findings obtained, considering a log-spiral failure mechanism under drained conditions and a circular mechanism for undrained conditions, could provide useful reference for the preliminary design of a two-stage layered slope.

This article proposes a graphical method associated with the g line to evaluate seismic slope stability. The g line depicts the combinations of c/γH and tanφ that are necessary to maintain slope stability at the critical limit state. Correlations of c/γH and tanφ are established based on the work-rate balance equation. Under a kinematic analysis, the pseudostatic upper-bound solution of c/γH is sought with an optimization procedure. After having determined the g line, the factor of safety for a specific slope can be easily estimated without the need for iterative calculations. For ease of practical use, a set of stability charts is presented. This approach also permits determination of the critical failure mode, including toe or below the toe.

This paper presents the observations during the UK Earthquake Engineering Field Investigation Team (EEFIT)'s post-earthquake reconnaissance missions to the September 20, 2009 Padang (M_w7.6), March 11, 2011 Tōhoku (M_w9.0) and April 16, 2016 Muisne (M_w7.8) earthquakes. The performance of buildings and geotechnical structures within the affected regions were investigated to gain insights on their design and construction deficiencies. Findings on these damages observed are compared along with the characteristics of the earthquake and nature of building codes in these countries. They include building damages attributed to a combination of structural resonance, deficiencies in reinforcement detailing, vulnerability to soft story collapse, ground settlement, soil liquefaction, and landslides. It was demonstrated that buildings which were severely damaged had natural building frequencies coinciding with the dominant frequencies of the ground shaking. The locations of damage of several such buildings showed insufficient confining reinforcements and lapping of stirrup links. Soft story collapses were also observed in the three earthquakes, although many were attributed to old building codes that were less effective. In areas affected by the Muisne earthquake, soft story collapses were mainly found at mid height of the building rather than at the ground floor as observed in the Padang and Tōhoku earthquakes, likely due to extension of building long after the bottom floors were completed. Such extension of building can either lead to local reduction in capacity due to weaker concrete-rebar bonding, possibly insufficient lapping of reinforcement, as well as increased axial loads. In the aspect of geotechnical failure, foundations of buildings found on piles performed reasonably well, except for areas affected by soil liquefaction. Landslides occurred following these earthquakes led to large concentration of casualties and property losses, motivating the EEFIT teams to invest efforts in hazard mapping and ground-truthing exercises using satellite images at Padang and Muisne earthquakes respectively. Such geospatial tools applied in these three earthquakes were reviewed and demonstrated to be capable of identifying landslide sites and producing reliable landslide hazard map.

Because of the heterogeneous layered characteristics of geomaterials, analysis of tunnel stability may be complicated, and such characteristics increase the possibility of progressive failure of the surrounding rock banks. This paper offers an analytical upper-bound approach to the analysis of the progressive collapse of deep rectangular tunnels based on three-dimensional (3D) velocity discontinuity surfaces. A symmetric 3D rotational progressive failure mechanism that considers the presence of rock layers partly induced by weathering is initially proposed and analyzed with the upper-bound theorem. In this approach, the range and shape of potential falling blocks are determined with use of the variational principle and the partition optimization method. The results obtained with the proposed approach showed good agreement and consistency with existing literature. Sensitivity analysis was also conducted to assess the effects of relevant parameters on the scope of impending blocks. Such analysis can also shed light on the collapse mechanism at failure and can be applied to projects under stratified or deteriorated rock masses, areas in which studies are limited at present.