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A circular arc test is described for determining the residual, or constant volume, interface strength parameters between soil and geosynthetics. The model is based on the variation of tension in a circular arc of fabric placed over a soil specimen and dead-loaded on two ends. The test method is simple and boundary conditions are well defined. The apparatus, theoretical formulation, and testing procedures are presented. The interface friction angle between dry Muskegon sand and three different materials: a cotton fabric, a fiber-glass mesh, and a nonwoven Geolon N35 filter, as determined by the circular arc test, are presented. Results of a staged circular arc test are also presented for the cotton fabric, and comparison to direct shear test results is made.

A laboratory testing apparatus is described for examining slopes subjected to seepage and stabilized by anchored geosynthetics (AGS). The AGS technique can increase the stability of cohesionless slopes such as coastal dunes against surficial erosion and shallow mass failure caused by wave action and seepage forces. In the AGS, a geosynthetic fabric is placed on the face of the slope and tensioned via anchorage to the ground. The required tension is achieved through frictional or pullout resistance of earth anchors that are fastened to the fabric and driven into the underlying soil mass. In the laboratory testing apparatus, however, AGS tensioning is provided by thin wires connected to rigid steel tubes that exert line loads on the fabric. The wires in turn are connected to dead weights “beneath” the slope that simulate anchor loads. The prototype slopes are failed by uniformly decreasing anchor loads while maintaining the seepage gradient and orientation constant. Very good agreement was observed between experimental results and theoretical predictions of the failure mode and the average AGS loads at failure.

This paper describes the measurement of the influence of capillary effects on the dynamic shear modulus of partially saturated sands. A Hall-type resonant column apparatus was used to perform the experiments. The materials tested included natural angular and subrounded sands, angular and subrounded sands with specified artificial gradations, and uniform angular and subrounded sands with various minus No. 400 sieve size fractions.Capillary stresses can significantly increase the shear modulus of unsaturated sands. Void ratio, confining pressure, degree of saturation, grain shape, and grain-size distribution are the primary factors affecting the shear modulus of partially saturated sands.