Volume replacement method for partitioning contents of rocks, soil particles and water mixture

Abstract: The effective measurement of the components in soil and rock mixture composition is of great importance in such studies and applications as agricultural production, civil and hydraulic engineering. This paper presents a volume replacement method for accurate measurement of soil, water and rock mixture components, including a series soil physical parameters measurement such as rock content and density, water content, soil bulk density, volume of soil air, porosity and void ratio. The measurement principle is based on the physic model of gas-liquid-solid composition in soils. Typically, soil consists of soil particles, rock fragments, water and air. A clay loam from Yangling of Shaanxi Province and a black soil from Jilin Province were used for the demonstrational measurements. The cleaned and dried rock fragments with the particle sizes of 5-10 mm were used for the experiments. Soil samples were prepared at 3 volumetric moisture contents as 10%, 15%, and 20%. The percentage volumes of rock mass were about 10%, 15%, and 20%. And the volumes of soil particles were designed as 40%, 45%, and 50%. Soil samples prepared were packed into the sampling rings of 100 cm3 in volume. The samples were placed into a constant volume container (CVC) with a known volume before it was weighted. Then the CVC was filled full of distilled water to replace air-filled space in the soil sample and the container, before it was weighted to determine the replaced air-filled space, and the total volume of rock, soil particles and soil water. The rock fragments were cleaned and dried before were weighted and put into the CVC to be filled full of water, so as to determine their volumes. The volumes and mass of soil particles and soil water were calculated after the volume and mass of rocks were determined. The volume of air was computed by the difference between the volume of sampling ring and the total volume of rocks, soil particles and soil water. After the soil samples were measured by volume replacement method, they were put into an oven to dry under 105℃ for 72 h to determine the mass of soil particles and soil water, to determine the soil moisture content and bulk density by using conventional oven-dry method. The air-filled volume in soil, as well as soil porosity and void ratio could be determined after measuring the volume of rocks, soil particles and soil water. The results measured by these two methods were compared. The results showed that the soil water contents measured by the volume replacement method with a CVC were higher than those obtained by the oven-dry method, with the relative errors about 5%. The measurement errors in soil bulk densities between the two methods were about 1%. The air-filled volumes of the soil measured by the 2 methods produced errors of about 2%. Compared with conventional oven-dry method, the relative errors in the measured soil porosities by applying volume replacement method were about 1%, and the measurement errors of void ratios were 1%-1.5%. The results indicate the feasibilities of accurate and effective measurement of soil particle and rock mixture components using the volume replacement method, which is the expansion and improvement for the previous measurement method by using fine-grained soils. Generally, for the measurement of soil particle and rock mixture composition, the proposed volume replacement method by using a CVC for a group measurement of soil physical parameters (soil water content, bulk density, soil air-filled volume, porosity and void ratio) in this study has such advantages as simple operation procedure, time efficient and low energy consumption. Besides, this volume replacement method with a CVC also can provide a helpful tool for the related experiments and measuring methods.