| Unsaturated soil is widely distributed in nature,and most of the sedimentary soil above the surface belongs to unsaturated soil.The research content of unsaturated soil mainly lies in its hydraulic parameters,namely soil-water characteristic curve and permeability function.In many practical projects,such as slope stability evaluation,dam leakage,underground migration of pollutants and other aspects,the relevant theory of soil-water characteristic curve is needed.Generally,it takes about one month to half a year to measure the soil-water characteristic curve.A dewetting curve takes a long time depending on the soil sample.Therefore,how to shorten the testing time of soil-water characteristic curve and maintain its testing accuracy has become a key issue in the field of unsaturated soil research.The main contents of this paper are as follows:(1)In this paper,the testing system of the pressure plate instrument based on the principle of axial translation technology is improved,and a bubble volume measuring system and a water storage-flushing system are added to enhance the sealing performance of the water container.The bubble volume measurement system consists of a switch,a pipeline and a glass tube with scales,which solves the measurement problem of bubble volume accumulated at the bottom of the clay plate.The water storage flushing system consists of large water storage containers,switches and some pipelines,which solves the flushing and saturation problems of the whole system and plays an indispensable role in bubble volume operation.The problem of water volatilization from the overflow water container in the original pressure plate meter system is improved,and the measurement error caused by water volatilization is reduced.(2)Based on the exploration of the principle equation of dynamic multi-step flow method by Yi Panpan and others,this paper introduces the establishment process of saturation time evolution equation in detail.The specific operation steps of establishing nonlinear fitting equations for Origin software are described.According to the established model,the unsaturated soil-water characteristic curve is obtained by solving the saturation time evolution equation.(3)The unsaturated soil-water characteristic curve test is carried out under the balance state when the original pressure plate instrument tests the silt sample,and the soil-water characteristic curve of the actually measured silt sample under the balance state is obtained according to the test.The time for measuring a dehumidification curve by using the method is about 90 days,which can be used as a standard curve for checking the correctness of the dynamic multi-step flow method for testing the soil-water characteristic curve.(4)A dynamic multi-step flow test is carried out on the silt sample on the improved pressure plate tester test system.The data automatic acquisition system records the change data of overflow water volume with time.The bubble measurement device measures the bubble volume accumulated at the bottom of the clay plate under each suction.The nonlinear fitting model is established in Origin,and the characteristic time and water holding rate C of unknown parameters are obtained by nonlinear fitting the measured data.After the SWCC of the excavated sample is measured,it is compared with the SWCC in the equilibrium state.The results show that the improved pressure plate meter system can be well applied to the dynamic multi-step flow test.The measured SWCC almost coincides with the curve measured in the equilibrium state,and the test time is only 5.2 days,thus shortening the test time and improving the test efficiency. |
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