Soil Arching in Sandy Slopes.

Abstract

Soil arching, the transfer of soil pressure from a yielding support to an adjacent non-yielding support, is a phenomena commonly encountered in geotechnical engineering. Soil arching theory traditionally has been applied to soils resting on horizontal supports or resting against vertical retaining walls. Arching theory has also been used to predict and explain stresses exerted by cereal grains in bins and silos with openings, i.e., yielding supports, at their base. Recently soil arching theory has been extended to the study of forces and stresses exerted by a yielding soil mass against discrete piles embedded in a slope and extending into a firm, non-yielding base. Numerous uses of discrete pile retaining wall systems exist in current geotechnical practice. In each case, soil arching has been relied upon to some extent as a means of stabilization without concise information as to the required spacing of the stabilization piles. This lack of information requires a design engineer to err on the conservative side, i.e., to place the piles closer together than they need be. The research reported here attempts to elucidate the role of soil arching in discrete pile retaining walls and to provide an information base for rational design. An experimental investigation was undertaken to obtain stress-deformation data in a sloping s and bed which was constrained from sliding by a series of fixed gates of variable width and spacing which were embedded at the base of the slope. The experimental data were needed to assess the validity of the modified and existing theories describing soil arching and related phenomena in slopes. A scaled down model of a sand slope made it possible to study experimentally the effect of varying several important parameters on the deformation and stress transfer behavior in the slope. The parameters chosen for study were selected on the basis of theoretical models proposed by several authors. A parametric variation or sensitivity study of the modelling equations was done to find the parameters that most affected the pressure or load on the gates. The parameters selected for investigation were: (1)Relative Density of S and ; (2)Gate Spacing (or size of opening between fixed gates); (3)Gate Width (or diameter of fixed gates); (4)Basal Friction Angle; (5)Internal Angle of Friction of S and . A number of soil arching theories, directly relevant to the present study, are reviewed and analyzed. The results of the experimental and theoretical comparisons indicate that discrete piles embedded into a firm, non-yielding base in a slope can provide significant additional stability to a slope if conditions for soil arching are met. Discrete support piles can be installed without unduly affecting slope stability during construction. For retaining walls that rotate vertically about the base between "fixed" side supports, theoretical predictions from the modified Bransby and Smith numerical method closely approximates experimental results. The stress transfer ability of loose soil is greater than previously thought. A loose deposit does not preclude the possibility of mobilizing soil arching or side friction. In soldier pile and lagging systems, material costs, strengths, and sizes can be optimized to achieve maximum benefit from soil arching.