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abstractThis paper presents the effect of a new type of geogrid inclusion on the bearing capacity of a rigid stripfooting constructed on a sand slope. A broad series of conditions, including unreinforced cases, wastested by varying parameters such as geogrid type, number of geogrid layers, vertical spacing and depthto topmost layer of geogrid. The results were then analyzed to find both qualitative and quantitativerelationships between the bearing capacity and the geogrid parameters. A series of finite elementanalyses was additionally carried out on a prototype slope and the results were compared with thefindings from the laboratory model tests and to complete the results of the model tests. The results showthat the bearing capacity of rigid strip footings on sloping ground can be intensively increased by theinclusion of grid-anchor layers in the ground, and that the magnitude of bearing capacity increasedepends greatly on the geogrid distribution. It is also shown that the load-settlement behavior andbearing capacity of the rigid footing can be considerably improved by the inclusion of a reinforcing layerat the appropriate location in the fill slope. The agreement between observed and computed results isfound to be reasonably good in terms of load-settlement behavior and optimum parameters.52365
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1. IntroductionThe use of geosynthetics to improve the bearing capacity andsettlement performance of shallow foundations has proven to bea cost-effective foundation system (Basudhar et al., 2007; El Saw-waf, 2007; Ghazavi and Lavasan, 2008). In marginal groundconditions, geosynthetics enhance the ability to use shallowfoundations in lieu of the most expensive deep foundations. Areinforced soil foundation (RSF) consists of one or more layers ofa geosynthetic reinforcement and controlled fill placed belowa conventional spread footing to create a composite material withimproved performance. A composite reinforced soil foundation(CRSF) is an RSF that also includes a geosynthetic fabric separatingnative soil from the fill used to construct the RSF.RSFs may be used to construct shallow foundations on loosegranular soils, soft fine-grained soils, or soft organic soils. MostRSF’s are constructed with the reinforcement placed horizontally;however, there are cases in which vertical reinforcement may beused. The reinforcement may consist of geogrids, geofabrics, geo-cells or other geosynthetics. The fill placed between layers of reinforcement is usually a clean coarse road base material that iscompacted to a minimum relative density of about 75%, but mayalso consist of compacted sand. There are a number of factors thatmay influence the performance of an RSF, including: (1) type ofreinforcement; (2) number of reinforcing layers; (3) depth belowthe footing to the first layer of reinforcement; (4) spacing betweenreinforcing layers; (5) dimensions of the reinforcement beyond thedimensions of the footing; and (6) type and placement of the fill.Over the past 20 years, considerable advances have been madeinto the understanding of the behavior of RSFs and on the appli-cations and limitation of using geosynthetics to improve theperformance of shallow foundations. Detailed investigations havebeen performed using small scale and large scale model footings toevaluate the performance of RSF’s and to develop rational methodsfor design.The subject of reinforcing soil underneath footings has acquiredconsiderable attention in the past few years (e.g. Dash et al., 2003;Boushehrian and Hataf, 2003; Ghosh et al., 2005; Bera et al., 2005;Patra et al., 2005, 2006). Through the possible applications, the useof foundation reinforcement to excellence load bearing capacityhas attracted a great deal of attention, and there have beennumerous studies on this subject (e.g. Binquet and Lee, 1975a, b;Akinmusuru and Akinbolade,1981; Fragaszy and Lawton, 1984; Daset al., 1994, etc.). These investigations have demonstrated that both 2. Laboratory model test2.1. Test configurationA series of laboratory model tests was executed in a test boxmade of a steel frame, having inside dimensions of 1.3 0.5 min plan and 0.6 m in height. The two sidewalls of the test boxwere constructed using transparent glasses for ease of moni-toring the failure mechanism during testing. In addition,a rough base condition of a 100 mm-broad model footing madeof steel was prepared at the bottom of the footing. The box wassufficiently rigid to remain plane strain conditions in thereinforced slope models. Since the walls of the test tank werefirmly held in position by steel melting and the wall frictionwas kept to the minimum, plane strain conditions wereconsidered for all model tests. Fig. 1 shows different parts oftesting apparatus.All tests were conducted with an artificially made slope of1(H):0.67(V). During testing, the model footing was loaded usinga lever mechanism with an arm ratio equal to 6 and using 10 kgweights. The footing load was applied by putting weights on thelever and displacements were measured by two dial gauges placedat two points on the footing. A schematic view of the testconfiguration with the symbols used in this study is illustrated inFig. 2.A model strip footingmade of steel with a series of ball bearings(see Fig. 3). The footing was 499 mm in length, 100 mm in width, B,and 10 mm in thickness. The footing was located on the crest ofsand slope in distance of 0.5B to the edge, with the length of thefooting equal to the full width of the tank.