(1. School of Civil Engineering，Hebei University of Technology，Tianjin 300401，China；2. Technology and Research
Center of Civil Engineering，Hebei Province，Tianjin 300401，China)
Abstract：A series of tests on mechanical performance of buried pipes protected by geogrids have been carried out under static load. The effects of relative density of soil surrounding buried pipes，Dr，embedment depth of buried pipes，H，length of reinforcement，L，layers of reinforcement，n，and embedment depth of the first layer of geogrid，u，on protection performance of buried pipes are investigated. The tests results show that the acceptable optimum values of u，length and layers of geogrids are 0.4B(B，width of loading plate)，4D(D，external diameter of pipe) and 3～4，respectively. While keeping the remained parameters identical，bearing capacity of buried pipes increases and settlement of loading plate decreases with the increase of relative density，but the rate of change for both decreases remarkably. This indicates that the function of reinforcement at lower relative densities is more effective than higher ones. Horizontal and vertical deformation along diameter direction increase with the increase of load，and vertical deformation is slightly greater than horizontal deformation. Furthermore，greater stiffness for soil surrounding pipes induced by increase of layers of reinforcement can disperse stresses effectively；it provides well effects of load-reduction for buried pipes. Additionally，measured hoop strains around buried pipes range from －1.5% to 1%. Through the measured strain values of buried pipes，it is obtained that compress strains appeared at the crown of pipes，and transition zone for strains changing from compress to tension falls in angle of 45 offside from crown of pipes，but tensile strains occur at the horizontal direction along diameter. When increasing relative density，hoop strains，which appear more obvious symmetrical，decrease. This demonstrates that increasing stiffness of soil itself due to higher relative density can inhibit movement and deformation of pipes.
2015, Vol. 34 
