Journal of Geotechnical and Geoenvironmental Engineering

The nonlinear response of shallow foundations when subjected to combined loading has attracted the attention of the research engineering community over the last few decades, providing promising evidence for incorporation of such response in design provisions. Failure in the form of soil yielding or foundation uplifting may accommodate high ductility demand and increase the safety margins of the whole structure. However, increased permanent displacement and rotation may occur. This paper explores the concept of shallow soil improvement as a means to locally increase soil strength and thus limit rocking-induced settlement. Bearing in mind that the rocking mechanism is relatively shallow, failure may be contained in a soil layer of known properties that extends to a shallow depth beneath the foundation. The performance of a system in poor soil conditions, on an ideal soil profile, and on improved soil profiles was explored through a series of centrifuge tests at the Center for Earthquake Engineering Simulation at Rensselaer Polytechnic Institute. The shallow soil improvement, evaluated in terms of moment-rotation and settlement-rotation response, proved quite effective even when its thickness was limited to 25% of the footing width. Some interesting similarities between poor, improved and ideal systems were observed in terms of cyclic moment capacity, contact pressure at the soil-foundation interface, and soil-foundation effective contact area. It is shown that even when uplifting is substantial and only 25% of the footing surface remains in contact with the soil, behavior in all four examined cases is quite stable—an important finding in seismic design of rocking foundations.

Currently, the suitability of centrifuge testing for capturing the thermal-induced mechanical behavior of full-scale energy piles has not been established, yet, despite their increasing worldwide development. Looking at this challenge, this paper investigates through thermomechanical numerical analyses the capability of centrifuge tests to reproduce fundamental aspects of the response of full-scale energy piles in dry sand when subjected to thermal and mechanical loads. The analysis proves the appropriateness of centrifuge tests for the considered goal and comments on crucial points that have to be considered when modeling energy pile-related problems.

Conventional stability analyses use various limit equilibrium (LE) methods to determine the minimum, critical factor of safety and its associated failure mechanism. These methods generally assume that collapse will follow predefined geometric constraints that are dependent on certain input criteria—an effective approach for simple geotechnical problems, but challenging in consideration of complex problems. An effective solution lies in the use of upper bound limit analysis (LA) in conjunction with a discretization procedure known as discontinuity layout optimization (DLO). Use of DLO-LA can be an effective tool for establishing a critical failure mechanism and its stability without the constraints or assumptions required in LE analyses. This study compares the use of LE (Spencer method with dynamic programming optimization, Morgenstern-Price, Spencer) and LA for several examples that focus on complex geotechnical scenarios to illustrate agreement and differences between the analyses, as well as situations where use of DLO-LA may be more appropriate. It is shown that LA can provide results that are comparable, and sometimes more critical, than rigorous LE while managing to handle complexities without the same assumptions regarding failure surface geometry or entrance/exit points of the slip surface. With the advance of accessible computer processing, engineers are at the point where more computationally intensive analyses like DLO-LA present a viable alternative to analyses that are dependent on potentially nonintuitive assumptions, especially for complex, yet realistic geotechnical problems.

The installation of underground trunk sewer lines in the Tuang formation of Kuching City, Malaysia, used trenchless technology in the form of the pipe-jacking method. The evaluation of pipe-jacking forces mainly involves empirical models developed for soils, with rather limited considerations for drives through weathered rock. Therefore, a novel approach is proposed to evaluate strength parameters by reconstituting and subsequently shearing scalped tunneling rock spoils in the direct shear apparatus. The direct shear results are then applied to a well-established pipe-jacking force model, which considers arching theory. The outcomes indicate that the backanalyzed frictional coefficients ${\mu }_{\mathrm{avg}}$ are not only reliable but also related to their surrounding geologies because of soil-structure interaction. This study also highlights the significance of lubrication and effect of rock arching in assessing jacking forces. The successful characterization of reconstituted tunneling rock spoils in this paper has shown potential use in assessing jacking forces during microtunneling works.

Internal instability occurs when the finer fraction from a well-graded granular soil escapes with the infiltrates, rendering a filter ineffective. Thus far, numerous particle size as well as constriction size distribution–based geometrical methods have been proposed to assess potential internal instability. This paper reports the results from hydraulic tests performed on six granular soils (five well-graded sand-gravel mixtures and medium sand) at different uniformity coefficients and compacted at varying relative density. The study facilitated an objective evaluation of some of the well known published methods, leading to a more realistic interpretation of filtration data based on a revised technique, which accurately demarcates the boundary between internally stable and unstable granular soils. A large body of published data and the current laboratory results were used to validate the proposed criterion for the assessment of internal instability, which is also sensitive to the relative density of the filter that has been ignored in most previous methods.

Bearing capacity factors because of the components of cohesion, surcharge, and unit weight, respectively, have been computed for smooth and rough ring footings for different combinations of $r_i/r_o$ and $\varphi$ by using lower and upper bound theorems of the limit analysis in conjunction with finite elements and linear optimization, where $r_i$ and $r_o$ refer to the inner and outer radii of the ring, respectively. It is observed that for a smooth footing with a given value of $r_o$, the magnitude of the collapse load decreases continuously with an increase in $r_i$. Conversely, for a rough base, for a given value of $r_o$, hardly any reduction occurs in the magnitude of the collapse load up to $r_i/r_o\approx 0.2$, whereas for $r_i/r_o>0.2$, the magnitude of the collapse load, similar to that of a smooth footing, decreases continuously with an increase in $r_i/r_o$. The results from the analysis compare reasonably well with available theoretical and experimental data from the literature.