A New Method For Measuring The Suction Of Unsaturated Soil

Suction is one of the important stress state variables that affect the strength and volume of unsaturated soil.Therefore,the measurement of soil suction is a prerequisite for understanding the behavior of unsaturated soils.Suction is a function of soil structure and soil water content.The relationship between soil suction(total suction,matric suction or osmotic suction)and water content(saturation or volumetric water content)is called soil-water characteristic curve.Soil suction can be determined by direct or indirect measurement techniques,although there are many techniques available to measure and control matric and total soil suction in the laboratory.However,almost all suction measurement methods have shortcomings in reliability,cost,scope of application,practicality and other aspects.Therefore,these soil suction measurement techniques need to be improved.This paper mainly through the dew point potentiameter,centrifuge and filter paper method of suction of unsaturated clay and sand soil mixture test research,this paper proposes a new measuring method of the soil suction of unsaturated soil,and the new method in this article involves the three traditional method compare,through theoretical analysis,review and summarize the data induce innovation penetration technology measure of the correctness and reliability of the unsaturated soil suction and limitations.The main research contents and results are as follows:(1)The dew point water potentiameter was used to measure the suction of soil mixtures with different ratios of clay(kaolin,bentonite)and sand in the process of dehydration and moisture absorption.The mathematical model in the form of two-parameter power function was used to simulate the soil-water characteristic curve,and the correlation coefficient was above 0.9.The experimental results show that there is hysteresis between the dehydration path and the hygroscopic path,the soil-water characteristic curve is unstable,and the suction value is related to the dehydration and hygroscopic path.In addition,the water holding capacity of bentonite was stronger than that of kaolin,and sand had almost no water holding capacity.In addition,the experiment found that the increase or decrease of suction was not only related to the particle size of soil,but also related to the water holding capacity and property of soil particles.(2)The soil-water characteristic curves of the soil mixture(100%K;90%K-10%S;80%K-20%S)were measured in 1,2 hours and 1,2,3 and 4 days by centrifugation.Experiments show that the experimental results obtained by the centrifuge are in good agreement with those obtained by the cold mirror dew-point water potentiometer.Centrifugal technology stabilized the soil sample to the suction equilibrium state in about 1 day.In addition,it was found that under the condition of high initial moisture content,sand and soil separation would occur under centrifugal action,leading to the deviation of the suction value.In the comparison of the difference between the suction of soil samples measured by WP4 C and that measured by centrifuge experiment,the data obtained by centrifuge experiment basically agree with the data measured by WP4 C,achieving the expected effect,which also indicates that WP4 C is reliable as a tool for analyzing soil suction.(3)In the filter paper experiment,the soil mixture of kaolin and sand was used as the research object.Whatman NO.42 quantitative filter paper was used,sealed and stored at 25? for at least 7 days.Compared with WP4 C,it was found that the suction measured by WP4 C was larger than that measured by WP4 C,with a deviation of 10%?16%.In the experiment using the filter paper method to test WP4 C as a method to measure the unsaturated soil suction,it was found that the WP4 C deviation was not large enough to meet the requirements of the suction measurement.(4)In the experiment of innovative osmosis technology,poly potassium salt and filter paper were used instead of polyethylene glycol solution and semi-permeable membrane in sealed containers to measure soil suction.Innovative penetration techniques require 3-5 days to measure suction,and this new technique overcomes the limitations of large suction measurements.Compared with the data obtained by WP4 C,the results show that the difference is small and the agreement is good.On the other hand,the innovative suction measurement technology is a better method to measure the high suction section in the laboratory,but the low suction section takes a long time,so it needs another design to apply the technology to the field measurement.