Since the cushion generally exists on the top and a substratum below the bottom of sand-drained ground,impeded boundaries were used to describe its effect on consolidation process of sand-drained ground.Assuming that ground deformation satisfies the condition of equal vertical strain and considering the radial variation of horizontal permeability coefficient,consolidation theory was established for sand-drained ground with top and bottom impeded boundaries under vacuum preloading.The series analytical solutions of consolidation degree and settlement were achieved by the separated variable method.The effect of the pervious coefficient of top boundary,the pervious coefficient of bottom boundary,the well resistance and the radial distribution feature of permeability coefficient on the consolidation degree and settlement of sand-drained ground were analyzed.The researches show that the final negative pore pressure and the effective stress exhibit a decrease with increasing depth of ground.When the other conditions are same,the ground with big bottom pervious coefficient has big consolidation degree,while it has small final settlement and the consolidation settlement at same radial consolidation time factor.When the bottom boundary of ground is impervious,the final settlement of ground hardlychange with the top pervious coefficient,but when the bottom boundary of ground is impeded or completely permeable,the final settlement increases with top pervious coefficient.The ground with big top pervious coefficient has big consolidation degree and consolidation settlement at the same radial consolidation time factor.Resistance of sand drain neither affect the final vertical distribution features of negative pressure,nor change the magnitude of the final settlement,while the resistance of sand drain can significantly decreases the consolidation degree of sand-drained ground and extends the finish time of consolidation.The radial distribution mode of permeability coefficient affects the consolidation degree of sand-drained ground.The consolidation degree of mode 1 is the biggest,mode 2 is the smallest,and mode 3 falls between mode 1 and mode 2.The effect laws of impeded boundary on the consolidation process of sand-drained ground under vacuum preloading are obviously different from those under surcharged preloading.
