Journal of Geotechnical and Geoenvironmental Engineering

A database of some 300 case histories of wall and ground movements due to deep excavations worldwide is presented. Although recognizing the weakness in the approach, a large database is used to examine general trends and patterns. For still soil sites, movements are generally less than those suggested in the well-known relationships proposed by Clough and his coworkers. However, for walls that retain a significant thickness of soft material but have a high factor of safety against basal heave, movements are similar to those calculated using the Clough charts. In these cases, when soft ground is actually present at dredge level, the Clough charts will underpredict movement and need to be used with care. For the above cases there is no discernible difference in the performance of propped or anchored systems but there is some evidence to suggest top-down systems perform better. In cases where there is a low factor of safety against excavation base heave, large movements can occur, but the Clough charts will give reasonable preliminary estimates of the likely movement in such cases. Cantilever walls have shown displacements that are often independent of the system stiffness. There is evidence to suggest that, in the case of cantilever walls and for all walls in stiff soils worldwide, design practice is conservative. Finally, the inclusion of a cantilever stage at the beginning of a construction sequence seems to be the main cause of unusually large movements.

This paper presents the results of analyses on the behavior of in situ walls, using the measured data collected from various deep excavation sites with multilayered ground conditions of soils overlying rock in Korea. A variety of in situ wall systems from >60 excavation sites were considered, covering a wide range of wall types, including H-pile, soil cement, cast-in-place pile, and diaphragm. The measured data were thoroughly analyzed to investigate the effects of wall and support types on lateral wall movements as well as apparent earth pressures. A series of 2D finite-element analyses were also performed to provide insights regarding the in situ wall behavior. Based on the results, lateral wall movements and apparent earth pressures are related to primary influencing factors affecting the wall behavior and information is presented in forms to provide tools that can be used for design and analysis.

This paper presents the results of a laboratory investigation performed to study the effect of soil heterogeneity on the removal of benzene from six different homogeneous and heterogeneous soil profiles using in situ air sparging. Air injected in homogeneous coarse sand profiles traveled in channels within a parabolic zone. Within fine gravel, injected air traveled in bubbles and was confined to a smaller zone of influence than within the sand profiles. Heterogeneous soil profiles were subjected to airflow patterns that were combinations of patterns observed in homogeneous soil profiles. When hydraulic conductivity differences between adjacent soil layers or inclusions were less than a factor of 10, air freely entered into the lower permeability soil regions. However, when differences were greater than a factor of 10, the injected air followed a path of least resistance and avoided regions of lower permeability. Regions that were subjected to high airflow were remediated rapidly as a result of efficient vapor-phase partitioning due to volatilization. Regions that were not subjected to high airflow, whether the result of locations outside of the zone of influence or airflow diversion due to permeability differences between adjacent soil layers/lenses, did not experience rapid contaminant removal and required rate-limiting diffusion for contaminant removal. Overall, the importance of determining the degree of soil heterogeneity at a given site with a detailed site investigation prior to implementing air sparging is demonstrated.

The magnitude of the passive earth pressure that resists the movement of a structure is controlled by the amount the structure moves and the direction in which it moves, strength and stiffness of the soil that resists its movement, friction or adhesion on the interface between the structure and soil, and shape of the structure. The Log Spiral Theory, corrected for 3D effects, provides an accurate means of computing ultimate passive pressures. A hyperbolic expression, together with estimated values of soil modulus and ultimate resistance, provides a means of estimating the relationship between structural movement and passive resistance. It is essential that the soil strength and stiffness used in making these estimates should be appropriate for the soil and the drainage conditions involved. The results of an undrained passive pressure load test in stiff sandy silt and a drained passive pressure load test in well-graded gravel are compared with passive pressures computed using the methods discussed. Reasonable agreement between the calculated and measured values shows that the Log Spiral Theory, corrected for 3D effects, and the hyperbolic load-deflection relationship provide an adequate means of estimating passive resistance for a wide range of conditions.

The purpose of this investigation was to identify and quantify the effect of numerous variables on the performance of fiber-stabilized sand specimens. Laboratory unconfined compression tests were conducted on sand specimens reinforced with randomly oriented discrete fibers to isolate the effect of each variable on the performance of the fiber-reinforced material. Five primary conclusions were obtained from this investigation. First, the inclusion of randomly oriented discrete fibers significantly improved the unconfined compressive strength of sands. Second, an optimum fiber length of 51 mm (2 in.) was identified for the reinforcement of sand specimens. Third, a maximum performance was achieved at a fiber dosage rate between 0.6 and 1.0% dry weight. Fourth, specimen performance was enhanced in both wet and dry of optimum conditions. Finally, the inclusion of up to 8% of silt does not affect the performance of the fiber reinforcement.

The possibility of a correlation between dynamic pore pressure increase p and dissipated energy density D in soils subjected to earthquake shaking has been the subject of speculation for nearly 20 years. While cyclic loading tests have tended to confirm the D-p hypothesis in the laboratory, no field confirmation has been given. In this paper compelling evidence is presented to support the D-p model from two real earthquakes. Downhole acceleration records from two earthquakes are analyzed to obtain approximate histories of shear stress, shear strain, and dissipated energy over a range of depths. The measured data were obtained from the Lotung downhole array in Taiwan and from the Sunamachi downhole array near Tokyo. Both of these arrays also contain pore pressure measurement devices, and records of pore-pressure increase during the earthquakes are available. Time histories of measured pore pressure will be directly compared with calculated values based on the D-p hypothesis. The results of this study suggest dissipated energy density may be remarkably well correlated with pore pressure increase in field situations.

A simplified method for estimating the ultimate bearing capacity of surface footings on sand is described with special attention to the dependency of the angle of internal friction of sand on confining stress. An extended slip line method is developed, in which the dependency of the angle of internal friction on the confining stress is formulated from results of conventional triaxial compression tests for various sands. Based on results from a comprehensive series of calculations employing the extended slip line method, the writers reappraise size effects on bearing capacity and investigate the relationship between strength parameters of sand and size effects on bearing capacity. A modified formula and several diagrams that provide a simple estimation method are proposed to consider size effects on bearing capacity. A comparison between estimations using the formula and ultimate bearing capacities measured from several series of centrifuge tests demonstrates the practicability of the proposed method for both strip and circular footings.

The results are presented of drained triaxial tests on a weakly bonded artificial soil in which the stress path direction has been changed partway through the shearing process. The effects of the previous shearing path history on the yield and failure surfaces are examined. Yield of the bonds occurs under each stress path direction followed, even when yield has previously occurred along another path. This demonstrates that bond breakdown is an anisotropic process. The position of yield was found to be independent of the previous shearing path history of the soil and occurred at points that corresponded to a yield surface defined for the current shearing path direction. However, the previous shearing path history of the soil did significantly affect the failure envelope. It is suggested that the bond yield surface is kinematic, in the sense that it is an expandable/shrinkable surface, but that it is not a moveable surface. It is postulated that the yield surface expands when volumetric strains are compressive and shrinks when the volumetric strains are dilatent.