tailieunhanh - DEVELOPMENTS IN HYDRAULIC CONDUCTIVITY RESEARCH Phần 5

Cơ học chất lưu, hay còn được gọi là cơ học thủy khí, nghiên cứu sự cân bằng và chuyển động của các phần tử vật chất vô cùng nhỏ có thể dễ dàng di chuyển và va chạm với nhau trong không gian. Với cơ học chất lưu, một cách tương đối có thể chia thành hai nhóm. | Hydraulic Conductivity and Water Retention Curve of Highly Compressible Materials - From a Mechanistic Approach through Phenomenological Models 105 larger than the air-entry value AEV . As a result materials like DBP shrink over a large range of suction values beyond the AEV. Model to determine the water retention curve of a highly compressible material A model was proposed to describe the WRC of highly compressible materials HCMs . The input parameters needed for the model were obtained directly from water retention tests. The experimental procedure used allowed to determine WRCs of materials undergoing significant volume changes during application of suction . HCM. Volume change in specimen was monitored during suction application so that volumetric water contents can be continuously calculated. The proposed WRC model was validated using published experimental data from tests performed with a compressible silty sand from Saskatchewan Canada. Hydraulic conductivity functions fc-functions based on the proposed WRC model fitted hydraulic conductivity values obtained from unsaturated permeability testing with this silty sand only for the data set that underwent no significant volume change verifying the model bias of Fredlund et al. 1994 s model Equation 16 for HCM explained in section As a result there is a need for an accurate model able to predict the fc-function of a HCM. The proposed WRC model was applied to experimental data from representative tests on DBP. The proposed model fits experimental data with good accuracy R2 . Volumetric water contents were significantly underestimated if volume change was eluded in the data reduction process. Void ratio of DBP specimens tended to converge to the same value as suction increase. Consequently their fc-functions should also superimpose. Based on their respective WRC curve parameters the fc-functions for several tests were predicted using the Fredlund et al. 1994 model coupled with function that .