High Suction Range Research Articles

Testing the Hydromechanical Behavior of a Compacted Swelling Soil

Abstract The paper presents a study of the hydromechanical behavior of a compacted swelling soil in a range of suctions comprised between 0 and around 300 MPa. To perform this study, two kinds of suction controlled oedometers were used, one using the osmotic method and the other using the salt solution method. A detailed review of the conditions for using these two methods is given in the first part of the paper. The second section provides the results of several suction controlled oedometer tests performed in this range of suction. They show that the mechanical behavior of the tested swelling material is strongly affected by the applied suction, even in the high suction range. In addition, it appeared that the samples preparation technique significantly influenced the hydromechanical behavior of the tested soil.

Automated Humidity System for Measuring Total Suction Characteristics of Clay

Abstract A computer-automated experimental system for determining total suction characteristic curves using relative humidity control is described. The system is applicable in the relatively high suction range important for fine-grained materials (7000 to 700 000 kPa). The new system has several advantages over existing suction measurement techniques; most notably, it is fully automated, has a much broader measurement range, is capable of determining both wetting and drying characteristics in significantly less time, and requires only one undisturbed sample for testing. Tests are conducted to evaluate the system response and illustrate its use in practice. Total suction characteristic curves are determined for four types of clay, ranging from highly expansive smectite to non-expansive kaolinite. Concurrent characteristic curves are determined using the filter paper method for comparison. Practical applications are demonstrated in two ways. First, select results are analyzed to assess the swelling potential of the four clays using an existing methodology based on total suction testing. Second, aspects related to the adsorption kinetics of expansive soils are evaluated by analyzing the results with a first-order kinetic model.

Automated Measurement of Total Suction Characteristics in High-Suction Range: Application to Assessment of Swelling Potential

An automated experimental system to characterize moisture-content-totalsuction relationships for unsaturated clayey soils is described. Unlike traditional techniques requiring independent measurement of total suction and moisture content (e.g., thermocouple psychrometry and filter paper), suction is directly controlled and corresponding moisture contents are continuously monitored. The system is applicable for total-suction values ranging between approximately 620 000 and 14 000 kPa. Total suction is controlled during testing by computer-automated rationing of “dry” and “wet” nitrogen gas in a closed environmental chamber. To develop characteristic curves, the equilibrium moisture content of soils placed in the chamber is measured with an integrated electronic balance as water vapor is absorbed or desorbed. The system requires no user intervention and is capable of generating characteristic curves, including wetting and drying loops, in a time span on the order of one to two weeks. Concurrent measurements using the noncontact filter paper method (ASTM D5298) are shown to agree very closely with those obtained from the automated system. Total-suction characteristic curves are compared for a highly expansive smectite clay and nonexpansive kaolinite clay. Hysteresis between the wetting and drying cycles and stepwise dehydration phenomena, which have been noted by previous researchers, are reproduced in the results. Comparison of the smectite and kaolinite characteristic curves demonstrates the system’s potential to become a simple, non-labor-intensive, quick, and reliable platform to qualitatively assess the relative swelling potential of clayey soils.

Modified Soil Water Retention Functions for All Matric Suctions

The Brooks‐Corey and van Genuchten functions were modified to adequately represent retention at all matric suctions. The modification consisted of replacing the residual water content with an adsorption equation (Campbell and Shiozawa, 1992). The modified functions retain the form of the original functions in the wet range and the form of an adsorption equation in the dry range. The modified functions provided excellent fits to data from six soils with textures ranging from sand to silty clay. The modified van Genuchten function can use previously determined parameters to obtain a reasonable representation of the high matric suction range, thus allowing for the use of existing parameter sets. The modified functions, as well as the function proposed by Rossi and Nimmo (1994), were combined with the Mualem conductivity model to generate closed‐form analytical expressions for the calculation of hydraulic conductivity.

高サクション領域における水分特性曲線の物理的外挿

高サクション領域における水分特性曲線の物理的外挿