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Estimating excavation-induced ground surface displacements in urban areas is needed to assess potential structure damage. Empirical settlement distribution models have been widely used to estimate the zone of influence and ground response behind braced excavation walls. Three underground station excavations, part of the Los Angeles Metro’s K Line Crenshaw/LAX Transit Project, offer a unique opportunity to collect field instrumentation data to improve estimates of ground deformations. One excavation employed cross-lot braces and soldier piles and wood lagging while the other two were supported by cross-lot braces and stiffer Cutter-Soil-Mixing (CSM) walls. For the excavations with stiff support systems and relatively small wall movements, upward surface displacement or heave governed the ground surface response, while surface settlement was measured at the excavation with the more flexible wall system. This heave behavior is often masked by settlement caused by relatively large wall movements, and is thus commonly disregarded. By idealizing the excavation unloading as an upward strip load at the ground surface, the Boussinesq solution for elastic upward movement can be used in combination with a settlement component resulting from lateral wall movements to estimate the magnitude and distribution of excavation-induced surface displacements. 

Soil piping is the gradual and progressive erosion of soil grains, causing a void (open pipe) to form as water flows through the soil. In dam engineering, this type of internal erosion is often referred to as concentrated leak erosion and has been a cause of failure at multiple dams. Soil piping has also been observed in many landslides and contributes significantly to soil degradation in hillslopes and agricultural areas. Despite these many important impacts, there is still limited understanding of how soil pipes develop and progress and what factors control pipe stability. One of the significant challenges with analyzing soil piping, or concentrated leak erosion, is that it typically occurs in the vadose zone, where unsaturated conditions are present. However, most studies examining internal erosion have focused on saturated conditions, and few studies have examined the role unsaturated hydraulic properties (i.e., air entry value, matric suction, etc.) may play in the likelihood of internal erosion. Consequently, this study aims to explore the mechanisms controlling the erosion rate within soil pipes from the perspective of unsaturated soil mechanics. Bench-scale experiments were performed to examine the formation and progression of an eroded pipe in a small slope constructed at different water contents. Soil samples were also tested to measure its unsaturated hydraulic properties. The results show that the likelihood of pipe formation varies with the moisture content and, therefore, suction in the soil, as does the potential for pipe collapse. This demonstrates that unsaturated soil properties are key to understanding the formation and progression of piping in slopes. 

This paper presents an experimental investigation related to the effect of Freezing-Thawing (F-T) cycles on the volumetric behavior of soils, with particular focus on the impact of the range of freezing temperatures on soils response impact. A reconstituted specimen made up from a commercial silt was subjected to F-T cycles in an 1D cell manufactured in a 3D-printer. The soil specimen was fully saturated, and the test was conducted under open system conditions inside an environmental chamber. Volume changes were recorded using a Linear Variable Differential Transformer (LVDT) during cyclic F-T. The test results show that the impact of the range of the freezing temperature is only relevant in the higher range of freezing temperatures (i.e. near the freezing point), and it tends to reduce significantly as the minimum temperature reduces. The study also shows that stress-history of the soil has a significant influence on the volumetric behavior soils subjected to F-T cycles