Ennio M. Palmeira

Backanalyses of geosynthetic reinforced embankments on soft soils

Abstract Geosynthetic reinforcement can be effectively used to increase the factor of safety of embankments on soft soils, particularly for shallow soft foundations layers. Several design approaches can be found in the literature dealing with the design of reinforced embankments on weak subgrades. Unfortunately, only a few well-documented case histories of reinforced embankments which led to failure have been reported. This paper presents backanalyses of some reinforced embankments that can be found in the literature using stability analysis methods commonly employed in routine works. Predicted values of safety factors at failure heights were close to one, and in spite of the limited amount of data available the results obtained suggest that these rather simple methods are useful tools for predicting factors of safety of reinforced embankments when the required input data are available and accurate. Nevertheless, even in these cases the backanalyses of the reinforced embankments suggest the use of factors of safety greater than 1.2 in routine works.

Effectiveness of geogrids as inclusions in cover soils of slopes of waste disposal areas

Abstract This paper presents an experimental investigation on the use of geogrids buried in cover soils of slopes of waste disposal areas using a large-scale ramp test. The tests involved the use of geogrids with varying values of tensile stiffness and bearing capacity (number of bearing members) installed at different elevations above the geomembrane resting on the ramp surface. The influence of the use of a geotextile layer on the geomembrane on the behaviour of the system was also assessed. The results show that the presence of a geogrid in the cover soil, and particularly of a geogrid with a geotextile on the geomembrane, can significantly reduce the deformability of the cover soil and the tensile forces mobilised in the geomembrane, as well as increase the inclination of the slope at failure.

A STUDY OF THE MECHANICS OF UNPAVED ROADS WITH REFERENCE TO THE EFFECTS OF SURFACE MAINTENANCE

Abstract This paper presents the results of laboratory model tests on reinforced and unreinforced unpaved roads on soft soil. Some aspects such as the influence of fill material, friction between the vehicle wheel and the road surface and reinforcement anchorage length have been investigated. Special regard was given to the influence of reinforcement on the performance of this type of road when subjected to periodical surface maintenance. A theoretical procedure to evaluate unpaved road performance under these conditions is also presented as a framework. The results obtained that the presence of the reinforcement greatly enhances the performance of the road after maintenance. This enhancement was observed to have been due to the wider deformed shape of the foundation surface when the reinforcement was present in comparison to the unreinforced case and to the type of reinforcemennt used which increased the drainage conditions at the top of the foundation layer.

STRESSES AND DEFORMATIONS IN GEOTEXTILE REINFORCED MODEL WALLS

Abstract This paper presents a study of geotextile reinforced model walls subjected to vertical surchange. Different reinforcemnt layouts were tested. Vertical stress distributions were measured at the base of the walls as well as internal displacements and horizontal displacements at the face of the wall. Comparisons between predictions and measurements were also made. The results showed that the reinforcement arrangement used in the wall can significantly affect its face displacements and the stresses at its base. Theoretical predictions of stresses and displacements in geosynthetic reinforced walls are sensitive to some soil or reinforcement parameters usually unavailable in routine works.

A modified gradient ratio test device

The gradient ratio test is used to assess soil-geotextile compatibility in filtration applications. Experience gained in performing the test is summarized for ten soils and four non-woven geotextiles, and the potential for application of the test method is demonstrated. Details of a new, modified test device are then presented which address a perceived limitation of the existing configuration of the test device. Results of a preliminary series of tests, performed to commission the modified gradient ratio test device, suggest the filtration behaviour of the geotextile is essentially independent of normal stress.

The Use of Alternative and Improved Construction Materials and Geosynthetics for Pavements

Traditional construction materials can be scarce or very expensive for several civil engineering works. Nowadays, significant increases in the cost of construction materials can also be a consequence of environmental restriction to their exploitation. Thus, there is an increasing interest on the use of low grade construction materials in pavements and other earthworks. This chapter deals with the use of alternative materials for the construction of pavements in association with low cost geosynthetics. Field test sections on a highway were constructed and monitored to evaluate the performance of the following pavement solutions: fine-grained soil stabilized with lime; quarry waste; poor quality fill material enveloped by a nonwoven geotextile impregnated with asphalt; and geotextiles as separation between the pavement base and the subgrade and between the base and the asphalt cap. A control test section where the pavement was constructed using good-quality gravel was also monitored. Several laboratory and field tests were performed throughout the research, such as laboratory tests under unsaturated conditions, field plate-load tests, field California bearing ratio (CBR), and pressuremeter tests. The results obtained show the potentials of the use of low-grade construction materials when appropriate construction procedures and geosynthetics are employed.

THE PERFORMANCE OF ALTERNATIVE GEOCOMPOSITES FOR DRAINAGE UNDER LABORATORY AND FIELD CONDITIONS

This paper presents a study on the use of geotextile filter in combination with alternative drainage materials in geotechnical and geoenvironmental works. Laboratory and field tests were performed using water and leachate as fluids, respectively. The alternative drainage materials consisted of PET bottle caps, tire strips and whole tires. Laboratory tests consisted of transmissivity tests under stress and the field experiments consisted of monitoring the performance of instrumented domestic waste cells with granular and alternative drainage systems. The results obtained show the potentials of the use of alternative drainage materials in combination with geotextile filters.

Chapter 26 The use of alternative and improved construction materials and geosynthetics in pavements

Abstract Traditional construction materials can be scarce or very expensive for several civil engineering works. Nowadays, significant increases in the cost of construction materials can also be a consequence of environmental restriction to their exploitation. Thus, there is an increasing interest on the use of low grade construction materials in pavements and other earth works. This work deals with the use of alternative materials for the construction of pavements in association with low cost geosynthetics. Field test sections in a highway were constructed and monitored to evaluate the performance of the following pavement solutions: fine-grained soil stabilised with lime, quarry waste, poor quality fill material enveloped by a nonwoven geotextile impregnated with asphalt, geotextiles as separation between the pavement base and the subgrade and between the base and the asphalt cap. A control test section where the pavement was constructed using good quality gravel was also monitored. Several laboratory and field tests were performed throughout the research, such as laboratory tests under unsaturated conditions, field plate load tests, field CBR and pressuremeter tests. The results obtained show the potentials of the use of low grade construction materials when appropriate construction procedures and geosynthetics are employed.

Geosynthetic Reinforced Walls and Slopes

Geosynthetics are synthetic materials used in geotechnical and geoenvironmental works. They are manufactured from different polymers and have a wide range of mechanical and physical properties serving different applications. Geosynthetics use polymers such as polypropylene, polyester and polyethylene. Table 1 and Fig. 1 summarise geosynthetic types, characteristics and applications.

BEHAVIOUR OF GEOGRID REINFORCED ABUTMENTS ON SOFT SOIL IN THE BR 101-SC HIGHWAY, BRAZIL

This work presents the behaviour of geogrid reinforced bridge abutments in the BR-101 highway, in the state of Santa Catarina, Brazil. Unidirectional geogrid layers were used as reinforcement for the embankments. A coarse sand was employed as fill material and the foundation layer consisted of an organic soft clay. Because of the nature of the foundation soil and the proximity of existing structures, geotechnical instrumentation was installed to assess the reinforced structure displacements. The results showed that the presence of the reinforcement layers reduced the soft soil lateral displacements and the damages to the existing structures. A preliminary stability analysis of one of the abutments is also presented and discussed.