RAPID MEASUREMENT OF SWCC BASED ON DYNAMIC MULTISTEP FLOW PRINCIPLE AND MODIFICATION OF PRESSURE PLATE INSTRUMENT

In this paper, the testing system of pressure plate instrument is modified using the principle of shaft translation technology. On the basis of the original testing instrument, we add an automatic data acquisition system, a water storage flushing system and a bubble volume measurement system. Data acquisition system consists of data acquisition software on computer, precision balance, water container and several pipelines. Its function is to automatically record the change data of overflow water quantity of soil sample with time. The function of the data automatic acquisition system is to record the change data of soil sample overflow water quantity with time automatically. The water storage flushing system consists of a water storage container, a switch and some pipelines. Its function is to flush and saturate the whole testing system. The bubble volume measurement system consists of switches, pipelines and glass tubes with scales. Its function is to measure the volume of bubbles overflowing from the bottom of the clay. According to the existing saturation time evolution equation in non-equilibrium state, we established a nonlinear fitting model on Origin software. The dynamic multi-step flow method is further used to test silt. We apply the next suction before this suction reaches without equilibrium. The measured data of overflow water volume changing with time is measured by the data automatic acquisition system. Then we turn on the bubble measuring system to measure the volume of bubbles at the bottom of the clay plate. After the bubble volume is measured, we convert the bubble volume into the weight of water. We use the weight of water got by bubble measuring device correct the data of water weight with time change, and then a more accurate change value of overflow quality with time can be obtained. According to the actual measured water weight change data with time, we obtain the saturation change curve with time. After non-linear fitting of saturation change curve data with the model previously established in Origin software, we can obtain the unknown parameter water holding rate C and characteristic time τ. Through the above steps, the soil-water characteristic curve under the equilibrium state is measured. We compare the soil-water characteristic curve measured by this method with the soil-water characteristic curve measured when the instrument is not modified. We find that the two curves can overlap to a large extent. It takes about 5 days to determine a SWCC curve under the dynamic multi-step flow method. However, the time for measuring a soil-water characteristic curve is generally three months to six months according to the different soil samples when the instrument is not modified. Compared with the two methods, the test method in this paper can save time to a great extent. Moreover, the test method is simple to operate, saving a lot of manpower and material resources, and is efficient and convenient.