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Column-supported embankments (CSEs) with or without basal geosynthetic reinforcement can be used in soft ground conditions to reduce settlement by transferring the embankment load to the columns through stress redistribution above and below the foundation subgrade level. CSEs are typically used to accelerate construction and protect adjacent facilities from settlement induced by the new embankment load. Mobilization of load-transfer mechanisms to the columns in a CSE requires differential settlement at the base of the embankment. When the embankment height is low relative to the clear spacing between columns, poor ride quality can occur because of unsatisfactory differential settlement at the surface of the embankment that result from differential settlements at the base of the embankment. Currently, there is no widespread consensus on the minimum embankment height required to avoid this type of distress. This paper describes a bench-scale test apparatus, materials, test procedures, and instrumentation that were used to improve understanding of how factors such as the spacing between columns, column diameter, presence and tensile stiffness of geosynthetic reinforcement, and loading on the embankment surface affect settlement at the surface of the embankment in response to differential settlement at the base of the embankment. The results of one test performed using a single column, and one test performed using a 5 by 5 square array of columns are presented to illustrate the type of information that can be obtained using the apparatus. Future publications will synthesize the results obtained from the testing program and provide recommendations for CSE design.

The large displacement shear box (LDSB) allows testing of interfaces as large as 711 by 406 mm (28 by 16 in.) with maximum interface displacements of 305 mm (12 in.). This device has been used to investigate the response of a variety of interfaces, including clay-geomembrane interfaces for which large displacements are important. The most recent application of the LDSB was to study the response of several sand-to-concrete interfaces under complex loading paths. In this application, the relevant characteristics of the LDSB are its geometry, which reduces the significance of end effects, its ability to apply monotonic and cyclic loading, and its ability to apply simultaneous changes in shear and normal stresses so that complex loading paths can be followed. This paper describes the main features of the LDSB, as well as the testing procedures and results of the sand-to-concrete interface tests that were performed. A procedure for normalizing the interface shear test data is also presented. This procedure facilitates comparative evaluations of interface response to different types of loading. The test results formed the basis for development of an extended hyperbolic model for interfaces that has been implemented in finite element analyses of soil-structure interaction problems.

Since World War II, the military has sought methods for rapid stabilization of weak soils for support of its missions worldwide. Over the past 60 years, cement and lime have been the most effective stabilizers for road and airfield applications, although many nontraditional stabilizers also have been developed and used. The most effective stabilizer to increase the strength of two soft clay soils within 72 h for contingency airfields to support C-17 and C-130 aircraft traffic needed to be determined. The treatment of one clay with cement resulted in relatively high unconfined compressive strengths (UCS), whereas treating the same clay with quicklime and calcium carbide resulted in lower UCS. The treatment of another clay with higher plasticity resulted in similar UCS for cement, quicklime, and calcium carbide. Secondary stabilizers, including sodium silicate, superabsorbent polymers, a superplasticizer, and an accelerator, were ineffective in increasing the UCS of a soil treated with cement, quicklime, or calcium carbide.

Since World War II, the military has sought methods for rapid stabilization of weak soils for support of its missions worldwide. Over the past 60 years, cement and lime have been the most effective stabilizers for road and airfield applications, although recent developments show promise from nontraditional stabilizers, such as reinforcing fibers. The benefits derived from fibers may depend on whether they are used alone or in combination with chemical stabilizers. The ability of stabilizers to increase the strength of two soft clay soils within 72 h to support C-17 and C-130 aircraft traffic on contingency airfields was investigated. Laboratory test results showed that longer fibers increased the strength and toughness the most for a clay treated only with fibers. For a clay treated with fibers in addition to a chemical stabilizer, shorter fibers increased toughness the most, but the fibers had little effect on strength. Higher dosage rates of fibers had increasing effectiveness, but mixing became difficult for fiber contents above 1%. Poly(vinyl) alcohol fibers were anticipated to perform better than other inert fibers because of hydrogen bonding between the fibers and clay minerals, but these fibers performed similarly to other fibers.

Compaction of backfill adjacent to stiff and unyielding structures induces earth pressures in the compacted fill that exceed normal at-rest earth pressures. A numerical method that can be used to calculate compaction-induced lateral earth pressures has been proposed by Duncan and Seed. The purpose of the study described in this paper is to evaluate the theory by comparing calculated and measured compaction-induced lateral earth pressures. The data for the comparisons is from values measured in backfills behind three stiff, unyielding walls: the instrumented retaining wall in the Transport and Road Research Laboratory in Crawthorne, England; the instrumented retaining wall in the Virginia Tech Geotechnical Laboratory in Blacksburg, Virginia; and the lock walls at Eisenhower and Snell Locks in New York state. The lock walls were found to be cracked, apparently by high earth pressures induced by compaction, and an extensive rehabilitation program was required. The measurements from all three walls confirm the existence of compaction-induced lateral earth pressures. For clean sand backfill, pressures calculated using the theory of Duncan and Seed are shown to be in reasonable agreement with measured values. Laboratory test data indicate that for moisture-sensitive silty sand backfill the applicability of the Duncan and Seed theory, which does not include considerations of pore water pressure development during backfill placement and compaction, depends on the degree of saturation of the backfill.