Geosynthetic encasement of individual stone columns can provide additional confinement to the columns thus increasing their load capacities and reducing lateral and vertical deformations. Most of past studies have been focused on the load capacities and settlements (i.e. vertical deformations) of the encased stone columns. However, the load transfer mechanism and the lateral bulging deformation pattern of the encased stone columns are not thoroughly understood. In the present study, four series of laboratory model tests in a large-scale testing tank were performed to investigate the effect of geogrid encasement on the lateral and vertical deformations of stone columns installed in a clay bed. For comparison purposes, ordinary stone columns were also tested and evaluated. The main objective of this research is to investigate the lateral and vertical deformation patterns of the encased stone columns and the reinforcement mechanisms of the geogrid encasement with different encasement lengths. In addition, the stress–strain characteristics of the encasement were measured and analysed. The test results show that the ultimate load capacity of the soft soil was greatly increased by the geogrid-encased stone columns. The effective length of the encasement was three to four times of the diameter of stone columns based on the consideration of performance and economy. In comparison with the analytical solution based on the unit cell concept with full encasement of columns, the experimental tests on composite foundations with partially encased columns, which allowed lateral deformations of columns and soils and slippage along the column-soil interfaces (geogrid–soil, stone column–geogrid, and stone column–soil if the column is not encased), resulted in larger settlements, especially at higher vertical pressures.

Finite element limit analysis (FELA) was used to investigate the bearing capacity of strip footing on a rock mass with single or multiple continuous voids. The underlying rock mass was assumed to have perfect plasticity and obey the modified Hoek–Brown criterion. A sensitivity study relevant to the material constants, such as intact rock strength, unit weight, and geological strength index, was also conducted; in addition, some other geometric parameters, including the location, size, width, height, and quantity of voids, were addressed. The results include presentations of a series of design charts and descriptions of the failure mechanisms.

Piles have been widely used to resist lateral loads in geotechnical engineering. In reality, piles are always embedded in layered soils; however, theoretical solutions for laterally loaded piles in multilayered soil system are limited in the literature. Based on the basic concept of the subgrade reaction theory, semianalytical solutions using the power series method were proposed to assess the behavior of a vertical pile with variable cross sections and embedded in a multilayered soil system to support lateral loads at its head. For the present method, the moduli of the lateral subgrade reaction were assumed to be of constant depth for clay soil and of linearly increasing depth for sandy soil. By considering the deflection and force continuum conditions along the pile length, a matrix form of pile response at any depth was expressed through the deflections and lateral forces at the pile head. The validity of the presented solution was verified by back-predicting behaviors of laterally loaded piles...

The discrete-element method (DEM) has been successfully used to simulate the behavior of granular material and was used in this study to analyze the stresses and deformations of a single geogrid-encased stone column under unconfined compression. The aggregate was simulated using graded particles of diameters ranging from 30 to 50 mm, and a biaxial geogrid as an encasement material was simulated using parallel-bonded particles. The micromechanical properties of the aggregate were determined using numerical triaxial tests at various confining stresses. The tensile properties of the geogrid were determined by a multirib tensile test, and the flexural rigidity of the geogrid was calibrated by a flexural bending test. This study investigated the changes in vertical and radial stresses and porosities, the contact-force distribution and particle movements within the aggregate, and the deformation and tensile force in the geogrid encasement. The load-displacement response of the DEM model of the geogrid-encased aggregate sample closely agreed with the experimental results. The coefficient of radial stress, defined as the ratio of vertical stress to radial stress within the aggregate, varied from 0.6 to 2.7 during loading where the tensile strength of the geogrid encasement was not fully mobilized. The aggregate showed volumetric contraction at small deformation and then dilation with an increase of deformation. The interlocking effects between the aggregate and the geogrid were observed at the initial state. The particles within the middle portion of the column were more likely to slip than those at other locations.

An axial compression was generated in a stone column under vertical loads on its top, and was often accompanied by a radial expansion against the surrounding soil near the top portion of the column. Considering this deformation characteristic of the stone column, an analytical solution for the settlement of the composite foundations reinforced with stone columns was presented. The load sharing between the column and the soil and the distribution of column-soil interfacial shear stresses was also incorporated into the solution. From the present solution, the vertical settlement and lateral bulging of the column under any applied loads can be evaluated at any depth. The validity of the solution was verified through the comparison with the measurement data and other existing analytical solutions. The influences of stress-concentration ratio, internal friction angle and cohesion of the surrounding soil, and the elastic modulus of the column on the deformations of the stone column were discussed. The l...

The properties of red sandstone, such as structures and compositions and disintegration characteristics, were investigated through a series of tests including laboratory tests, a large-scale simulated experimental test, and tests in a section of a highway in China. With the disintegration tests, red sandstone was classified according to its engineering properties. With the understanding of the properties of red sandstone, the filling methods, and the construction techniques of roadbeds and embankments, including quality control and quality examination with associated criteria, were developed. This paper confirmed that these techniques can be successfully applied to solve a series of difficult problems in highway construction in red sandstone regions with considerable potential economical benefits and significant technological and engineering values.