ICE - Institution of Civil Engineers - Virtual Library

This paper presents the results of gradient ratio tests on different soil–geotextile systems under normal stresses up to 2000 kPa. Different types of soil and geotextiles were tested, and the soil particles that passed through the geotextile and those retained in it were collected for particle size analyses. The results obtained show that the use of definitions of gradient ratio based on the measurement of water heads close to the geotextile layer can be useful for a better identification of geotextile-clogging mechanisms. The entrapment of soil particles in the geotextile increases its retaining capacity and alters the conditions for further clogging. The dimensions of the entrapped soil particles can be greater than the geotextile pore dimensions under unconfined conditions and are controlled by soil and geotextile characteristics and by the soil sample preparation technique employed. The results suggest that current retention and permeability criteria for geotextile filters can be excessively conservative. Discussions on geotextile performance in the test and under field conditions are also presented as well as limitations and new proposals for the interpretation of the gradient ratio test.

This paper presents a pseudo-static-based approach for evaluating the mechanical effects of facing components on the seismic displacement of reinforced soil walls backfilled with cohesionless soils. The proposed method is used to examine some factors that may influence the seismic stability and/or displacement of a 5 m high idealized wall, such as the connection strength at the facing–soil interface, the shear strength of the facing, the shear strength of the backfill soils, and the length of the reinforcement. Seismic displacement charts are established for a 5 m high idealized reinforced wall with various types of facing subjected to four different ground excitations. These charts are then verified using wall displacements measured after a major earthquake, and can be used to facilitate preliminary performance-based seismic designs of reinforced soil walls. Analytical results show that a conventional ‘two-wedge’ analysis greatly underestimates the seismic stability of a wall with a structural facing component because the interaction between the facing and the retained soils is ignored. The connection strength between the facing and the reinforcement may significantly increase the seismic stability and/or reduce the seismic displacement of the investigated wall provided that a specially designed facing–geogrid connection is used, which enables very high connection strength to be developed. The interblock shear strength of discrete-type facing affects the seismic stability of the wall only in a secondary way, because higher interblock shear strength may cause a failure mechanism that passes through the bottom of the wall. The unit weight of the facing plays a moderate role in the increase of the seismic stability of the 5 m high wall with vertical facing. It is also shown that the advantage of using a structural facing may vary according to changes in the internal friction angle of the backfill and the length of reinforcing material.

This paper presents equations for calculating the rate of liquid flow through defects in the geomembrane component of a composite liner. The considered defects have a uniform width and have a length that is finite or infinite. Two types of defects are considered: narrow defects such as tears, cuts and defective seams, and wide defects, such as damaged wrinkles. As a first step, the paper presents a new expression for a previously published equation for the rate of liquid flow through an infinitely long defect in the geomembrane component of a composite liner. This new expression is significantly simpler than the original equation. The new expression is then combined with empirical equations for the rate of liquid flow through a circular defect in the geomembrane component of a composite liner to obtain equations for the rate of liquid flow through a defect of finite length in the geomembrane component of a composite liner. The rate of flow through defects of finite length comprises two components: flow that takes place over the length of the defect and flow that takes place at the two ends of the defect. A parametric study shows that, in most cases, a large fraction of the flow takes place at the ends of defects of finite length. Therefore, it is generally not recommended to do a two-dimensional calculation, thereby neglecting flow at the ends of the defect. Examples of use of the proposed equations are presented.

This technical note presents empirical equations for the evaluation of the rate of advective flow through composite liners, i.e. liners comprising a geomembrane and a low-permeability soil layer. The advective flow considered is due to large circular defects in the geomembrane. The flow rate depends on contact conditions between the geomembrane and the soil layer. Three types of contact conditions (excellent, good, and poor) are considered. The methodology for developing the empirical equations is identical to the one proposed by Touze-Foltz and Giroud for small circular defects. The methodology consists in determining values for the unknowns of the empirical equations such that flow rates calculated using the empirical equations are as close as possible to flow rates rigorously calculated using existing analytical solutions. This was achieved by conducting numerical calculations for more than 38,000 cases defined by a wide range of values of the parameters (contact conditions, soil layer thickness and hydraulic conductivity, and hydraulic head).

This paper presents graphical solutions for estimating geosynthetic loads in geosynthetic–soil layered systems on slopes. The graphical solutions are based on a simple analytical approach that maintains strain compatibility and force equilibrium. The solutions are presented graphically using dimensionless terms that incorporate the loading conditions and material properties. An illustrative example is provided to demonstrate how the graphical solutions are used.