Journal of Geotechnical and Geoenvironmental Engineering

Four centrifuge tests were performed to investigate the reinforcing mechanisms of soil-cement columns in liquefiable sand. Two unimproved baseline models and two models improved with soil-cement columns were subjected to sine sweep and earthquake base motions of varying intensities to observe acceleration, pore pressure, lateral displacement, and settlement responses. The dynamic records were processed to derive the effective natural frequency of the profiles and to obtain the dynamic stress-strain responses for unimproved and improved soil. It was found that the shear reinforcement mechanisms of columns was not effective in reducing cyclic stress ratios in the treated soil; liquefaction triggering occurred nearly at same time for both unimproved and improved soil cases and the magnitude of the resulting soil settlement was not significantly reduced. When the bases of the columns were free to rotate, the columns rocked within the soil and produced negligible shear stiffening of the soil profile. When the bases of the columns were fixed against rocking, the columns deformed primarily in shear and flexure but the observed increase in natural frequency of the improved profile was much smaller than predicted by assuming shear strain compatibility between the columns and soil. Design equations that account for shear strain incompatibility are shown to give reasonable estimates for the observed natural frequency of the improved soil profile, and these equations suggest that the associated reduction in cyclic shear stress in the improved soil is small. The soil-cement columns did, however, remain intact and would have provided a means for supporting overlying structures even after liquefaction was triggering in the soil.

Thermal conductivity is a fundamental physical property governing heat transfer in soil. It depends on soil types, pore structure, temperature, and moisture content, and can vary over an order of magnitude. Some theories have been established to address the effect of temperature on thermal conductivity. Other theoretical works focus on the effect of moisture content on thermal conductivity of different sandy and loamy soils. This work addresses the effect of all soil types and moisture content on thermal conductivity for ambient temperatures from 20 to 25°C. Thermal conductivity varies little within the hydration and capillary regimes, varies moderately within the funicular regime, and varies greatly within the pendular regime. A closed-form equation is proposed and validated by explicitly considering the soil-water retention regimes. Results taken from the literature for 25 soils and from the current study for two clay soils show that the closed-form equation can accurately predict thermal conductivity of all types of unsaturated soil.

Reinforced soil composites and mechanically stabilized earth (MSE) walls are frequently employed to carry large surcharge or footing loads. For the safety and serviceability of these reinforced soil structures, it is necessary to analyze the reinforcement load and compression of reinforced soil mass subjected to surcharge loading. In the research reported in this paper, an analytical method proposed by the writer was extended to meet these needs. The extended analytical method explicitly considers soil nonlinearity, soil dilatancy, soil-reinforcement interaction, and end restrictions of reinforced soil mass. Both plane-strain and triaxial stress states can be considered in the method. The applicability of the method for reinforcement load was validated against eight large-scale tests of reinforced soil mass or MSE walls, and the method for reinforced soil compression was validated against two large-scale tests. The compressions of four reinforced soil minipiers under surcharge loading were also predicted. The proposed method has the capacity to unify the analyses of reinforcement load and compression of a reinforced soil mass under low to medium surcharge loading. Some issues in the application of the proposed method are also discussed.

The frequency dispersion characteristics of pile barriers are receiving more attention due to their effectiveness and a better understanding of their behavior at attenuating middle and lower frequency ground vibrations. Based on a comprehensive study, this paper proposes a two-dimensional periodic pile barrier system, which can produce low-frequency or middle-frequency attenuation zones (AZs). Periodic pile barriers are composed of periodically arranged hollow piles filled with either soft or hard in-fill materials. Finite element method and plane wave expansion method are first used to study dispersion curves, AZs, and corresponding wave dispersion mechanisms. Influencing factors of the periodic pile barrier on the AZs are then identified based on a parametric study. To further illustrate the effectiveness of the vibration attenuation, a three-dimensional pile–soil finite element model with combined periodic pile barriers is analyzed, and the frequency ranges of vibration reduction are found to be consistent with the AZs of the corresponding dispersion curves. The present numerical results are in agreement with existing experimental and numerical results, which validate the existence of AZs in periodic pile barriers. This study provides a new insight into the analysis and design of pile barriers to block vibrations, especially in the low-frequency range.

Microbial induced calcite precipitation (MICP) is a novel biomediated ground improvement method that can be used to increase the shear strength and stiffness of soil. The evolution of the shear strength and stiffness of sand subjected to undrained and drained shearing is evaluated using triaxial tests. MICP treated sands with cementation levels ranging from young, uncemented sand to a highly cemented sandstonelike condition are subjected to undrained shear. A transition from strain hardening to strain softening behavior and a corresponding transition of global to localized failure as cementation is increased is observed. Moderately cemented specimens are subjected to various stress paths, which result in a change to the shear strength and volumetric behavior. Shear wave velocity is used to nondestructively monitor the change in small-strain stiffness during shearing, which provides an indication of cementation degradation as a function of strain level. Because shear wave velocity is influenced by both the level of cementation and the change in effective mean stress during shearing, the normalized shear modulus is used to evaluate the degradation of cementation during shearing.

Driven piles are used widely both offshore and onshore. However, accurate axial capacity and load-displacement prediction is difficult at sand-dominated sites, and offshore practice is moving towards cone penetration test (CPT) based design methods developed from instrumented pile research and database studies. However, onshore use of these methods remains limited; there is a paucity of high quality case histories to assess their potential benefits clearly, and application in layered profiles may be uncertain. This paper presents new tests on prestressed concrete (PHC) pipe piles driven in sands for a major new Yangtze River bridge project in China, assessing the performance of the ‘new CPT’ and conventional capacity approaches, considering the influence of weak sublayers on base resistance and noting the marked changes in shaft capacity that apply over time.

Any new tunnel excavation may damage adjacent existing tunnels in congested cities. To evaluate the impact of new tunnel construction on nearby existing tunnels, a series of three-dimensional centrifuge model tests were conducted with numerical backanalyses using an advanced hypoplasticity constitutive model. The influences of the pillar depth-to-diameter ratio (P/D) on two-tunnel interaction and the effects of shielding on three-tunnel interaction were investigated. The maximum measured settlement of an existing tunnel caused by a new tunnel excavation at P/D of 0.5 underneath was approximately 50% larger than that when P/D was 2.0. This is attributed to a smaller mobilized shear modulus, resulting from a larger reduction in confining stress of soil acting on the invert of the existing tunnel in the former than in the latter. When the new tunnel was excavated underneath two perpendicularly crossing tunnels, the lower existing tunnel “shielded” the upper one from the influence of tunnel excavation. As a result, the settlement of the upper existing tunnel was 25% smaller than in the case without the shielding tunnel.

Conventional bearing capacity analyses for shallow foundations placed on slopes use a modified set of bearing capacity factors based on soil properties, footing geometry, and slope configuration, but are restricted to purely cohesionless or purely cohesive soils. This approach is adequate for establishing bearing capacity on engineered fills with controlled foundation properties, yet does not adequately address design for bearing capacity on soils that have both cohesion and internal frictional resistance—a common scenario for native soils. This role becomes increasingly important in design for mechanically stabilized earth walls, which are often placed on slopes of native $c^{\prime }\text{-}{\varphi }^{\prime }$ soils in which the bearing capacity can often be the critical design constraint. Prior approaches to bearing capacity on horizontal ground for $c^{\prime }\text{-}{\varphi }^{\prime }$ soils utilize principles of limited state plasticity in their formulation, yet the most commonly applied bearing capacity approaches on slopes use semiempirical formulations that employ mutually exclusive soil strength parameters. In this work, results are attained using upper-bound limit state plasticity failure discretization scheme, known as discontinuity layout optimization (DLO), which uses nonassumptive failure geometry (under translational kinematics) in its formulation. The values presented demonstrate important components in consideration of bearing capacity for strip footings placed adjacent to slopes of $c^{\prime }\text{-}{\varphi }^{\prime }$ soils, in particular, the relationship between soil strength properties, slope height to footing width ratio, slope angle, and critical collapse mechanism. A set of reduction coefficients that can be directly applied to the classical bearing capacity formulation is presented for ease of application.

The San Jacinto Monument was built in 1936 to celebrate the 100 year anniversary of the battlefield victory that gave Texas its freedom. Ray Dawson was in charge of the foundation design and decided to instrument the foundation to monitor the settlement of the Monument. The settlement has been recorded since 1936 and provides a very valuable long-term record. This settlement and other geotechnical data were studied and reported by Briaud and his co-authors in 2007. That study was based on data available at the time, which was primarily from a 61-m-deep boring in 1953. In 2007, Fugro and Texas A&M University drilled a new boring with sampling to a depth of 78 m, conducted in situ tests to 36 m, and laboratory tests on the samples recovered. Updated settlement calculations are provided using this new data; they show reasonably good agreement with modern settlement techniques. One of the issues possibly affecting the settlement readings is the subsidence of the ground surface, which can reach 3 m in that area of Houston. A second part of this article presents calculations and numerical simulations to evaluate the influence of subsidence on the recorded settlement of the Monument. It is shown that the true settlement of the SJM is 295 mm while the measured settlement is 328 mm. The reduction is due to the different influence of the subsidence on the settlement of the shallow benchmark and of the Monument.

Construction of new highway embankments in urban areas often requires building over existing underground utilities and lifelines. Embankments constructed over such utilities often induce substantial additional earth pressures causing overstressing and/or unacceptable deformations of the buried pipes, resulting in interruption of service for both the utility and highway. There are several techniques that can be used to mitigate this problem. Geogrid-reinforced bridge platforms are one of the newer techniques to deal with this problem. In order to gain a better understanding of the earth pressure reduction that may be achieved by geogrid bridging, the Ontario Ministry of Transportation (MTO) constructed an instrumented full-scale test embankment over a geogrid-reinforced bridged trench. In this paper, the results of this full-scale test along with a numerical study to evaluate the stress reductions achieved by the use of geogrid bridging platform installation are reported. In addition, results of a parametric study to investigate the soil structure interaction of the proposed stress reduction system and its effectiveness on the reduction of the deformations, moments, and normal forces of a buried culvert are presented.

A series of laterally loaded pile tests carried out both in natural ground and in cemented treated soil is presented in this paper. The length to diameter ratio $L/D$ of the piles was selected as 5, representing the behavior of a free-headed, short pile that will move as a rigid body in the direction of the applied load without structural damage. The extent of the treated soil layer around the pile ranged from 2–4 times the pile diameter and 0.1–0.3 times the pile length. The treated layer was a mixture of Osorio sand and early strength portland cement. Experimental results show a significant increase in lateral load resistance of short piles when the soil is treated with cement.