The Experimental And Theoretical Research And Its Application Of Geobelt Reinforced Gravel Cashion Foundation

This paper provides an experiment and theoretical research basis for further applying of geobelt reinforced gravel soil cushion to building foundation. According to the large-scale triaxial tests and in-situ load tests,the effects of different reinforcement parameters on the working properties of geobelt reinforced gravel cushion foundation are investigated and analysed in detail. By theoretical research and engineering application of geobelt reinforced gravel soil, a calculation formula of foundation bearing-capacity on geobelt reinforced cushion is drawn out.At first, The large-scale triaxial consolidated drained shearing tests have been carried out for geobelt reinforced crushed gravel soil and non-reinforced crushed gravel, in which is real geobelt used in engineering project was instead of thin net clothes. The results can fully reflect the relationship stress-strain of geobelt reinforcement gravel soil. Meanwhile large load tests in site have been carried out for belt geosynthetic reinforcement gravel layers which is the first maked use of to building foundation geobelt reinforcement cushion in China. The effects of reinforced parameters on the geobelt stress, average soil pressure distribution under layer and foundation bearing capacity was studied.Secondly, by the study analysis of test results and practical use ofproject, a calculation formula of foundation bearing-capacity on geobelt reinforced cushion is provided. It considers overall reaction of reinforced parameters including: geobelt material; N- numbers of reinforcement layers; U-distance from footing bottom to top reinforcement layer; H-the distance between the two layers of geobelt; LDR-the linear density ratio. This formula can be applied to strip and rectanglar foundations.Thirdly, the experimental results have discovered that (1) constitutive relation of geobelt gravel is accord with Duncan-Chang non-linear model. Mechanism of geobelt reinforced cushion gravel obeys the principle of "quasi-cohesion". It is seen that the strength envelopes for reinforced and non-reinforced gravel are almost parallel, so their friction angles are fairly same, and the cohesion of the reinforced soil is higher than that of non-reinforced soil; (2) the soil stress distribution of reinforced layers is obviously increased after reinforced, the bearing capacities of the reinforced composite foundation are improved and the settlement are reduced. Thus it is suggested that the angle of stress distribution of geobelt reinforcement layer may be free from the limit in "Chinese code for design of building foundation"(GB50007-2002), that is, when Z/B<0.25 the angle of stress distribution is 0; (3) reinforcement results is relation to reinforced parameters, geobelt material and confining pressures. Following reinforced parameters influence the reinforcement results, properties of geobelt material; reinforcement numbers (N); distance from footing bottom to top reinforcement layer(U); the distance between the two layers of geobelt(H); the linear density ratio(LDR). (4) For Taiyuan region, TG glass-plastic geobelt material the optimum reinforced parameters given follows: N=2;U=0.17Z;H=0.33Z;LDR=33.3% (Z is geobelt cushion thickness) .Finally, the nonlinear FEM analysis for reinforced composite soil is done by using composite modulus method. The geobelt reinforced cushion is regarded as an uniform soil and in good agreement with Duncan-Chang nonlinear model, when the surround soil trends to Drucker-Prager elastic-plastic model. By FEM analysis, this paper discusses the strength-deformation relation of geobelt reinforced cushion and the distribution of soil pressure under cushion, with different reinforced parameter. The FEM computational results and the observed results of in situ tests are in good agreement. It is proved that FEM calculation model is accuracy and the calculating parameters is reasonable. .