Ujwalkumar D. Patil

Characterization of Compacted Silty Sand Using a Double-Walled Triaxial Cell With Fully Automated Relative-Humidity Control

A fully automated relative-humidity (auto-RH) control unit has been adapted to a newly implemented double-walled triaxial cell to test unsaturated soils under higher total suction states via the vapor-pressure technique, allowing for direct measurement and control of the relative humidity inside the pores of the test soil. The triaxial system is also suitable for implementing the axis-translation technique. With the operational and fully integrated servo-controlled triaxial system, a series of conventional triaxial compression (CTC) tests were conducted on identically prepared specimens of compacted silty sand under constant total suction states of 20 MPa and 300 MPa, induced and controlled via the automated auto-RH control unit. The suitability and reliability of the integrated system was demonstrated by closely repeatable results obtained from the series of suction-controlled CTC tests. Suitable shearing rates for suction-controlled testing of compacted silty sand, via both axis-translation and relative-humidity-based techniques, were also empirically assessed through a series of strain-/suction-controlled tests. The latter were conducted at different axial loading rates (% axial strain per unit time) under either constant matric suction (0.5 MPa) or constant total suction (300 MPa). In both cases, the most suitable shearing rate was identified as the maximum rate for which the test soil continued to be subjected to a constant matric or total suction throughout the entire shearing stage.

Assessment of suitable loading rate for suction-controlled triaxial testing on compacted silty sand via axis-translation technique

State-of-the-art automated triaxial test systems have allowed for testing of saturated and unsaturated soil specimens along sophisticated stress paths. Selection of an appropriate shearing rate is crucial in the accurate determination of shear induced volume changes in the specimen, and making sure that there is no bifurcation of the target effective stress path from the measured stress path. However, in triaxial testing of unsaturated soils (UNSAT testing) at constant suction values, the axial shearing rate should also be slow enough to maintain equilibrium of matric suction as well as uniformity in water content throughout the shearing stage. In this case shearing rate is mostly controlled by the high-air-entry ceramic disk, regardless of how pervious the soil is. The maximum suction that is to be applied during the test program at highest confining pressure has to be chosen to quantify this rate. In medium to dense silty sands, with tendency to dilate upon shearing, it is essential to have shearing rates slow enough to permit upward flow of water into the specimen through the low-permeability ceramic disk. As part of an ongoing research on statically compacted unsaturated silty sands at UT Arlington, the suitable shearing rate is determined empirically through a series of strain-controlled UNSAT Triaxial CD tests at three axial shearing rates (0.014%/min, 0.0086%/min and 0.0029%/min), with highest suction applied via axis-translation technique. The most suitable shearing rate would be the maximum rate for which the specimen is subjected to constant matric suction throughout the test, with induced axial strains similar to those induced at lower shearing rates. Importance of assessment of suitable loading rate during shearing stage (henceforth called as shearing rate) has been long well recognized as it affects the strength, stiffness and volume change behavior of unsaturated soil specimens during triaxial testing. Effective strength parameters in geotechnical design are usually obtained via consolidated drained (CD) or consolidated undrained (CU) tests. Due to the growing evidence of increase in strength due to matric suction, there is a need to modify the conventional triaxial test apparatus to accommodate unsaturated testing along with saturated soil testing. In unsaturated soil triaxial testing, the pore air and pore water

Modeling Essential Elastoplastic Features of Compacted Silty Sand via Suction-Controlled Triaxial Testing

AbstractExperimental results from a comprehensive series of suction-controlled, consolidated drained (CD) triaxial tests, conducted on statically compacted specimens of unsaturated silty sand, are presented. The experimental program was accomplished in a newly implemented, fully automated double-walled triaxial test system via the axis-translation technique. Results were thoroughly analyzed to gain critical insight into some of the essential elastoplastic features of compacted intermediate geomaterials under controlled suction states, including the effect of suction on yield stress, apparent cohesion, tensile strength, and critical state line, as well as postpeak softening and strain-induced dilatancy under suction-controlled monotonic shearing. Constitutive parameters postulated by the Barcelona basic model (BBM) were then experimentally calibrated and used for prediction of compacted silty sand response at matric suction states that varied from 50 to 750 kPa. Predicted values of deviatoric stress at cri...

Resilient Modulus of Liquid Chemical-Treated Expansive Soils

Diluted acids are used as chemical stabilizers in Texas to treat expansive soils for residential projects via deep injection. Due to the proprietary nature of the chemical stabilizers, there are very limited studies on the resilient modulus (MR) of chemically-treated expansive soils. This paper evaluates the effect of a liquid chemical stabilizer on the treatment of expansive soils collected from Texas and Colorado. The chemical solution, called ionic soil stabilizer (ISS) which contain sulfuric acid, phosphoric acid, citric acid, and water was used as an additive and tests were carried out on untreated and treated bulk soil samples in accordance with AASHTO T-307. The treated soil specimens were prepared by hand mixing the dry soils with the chemical stabilizer at three application ratios and two curing periods (7 and 28 days). The experiment results show that the value of resilient modulus increases with the increase of chemical application ratio. The resilient modulus of the treated sample cured for 28 days is much higher that of the untreated sample. Also, MR test results were found to be highly dependent on the compaction, moisture content, chemical ratio and curing time. Finally, MR test results are compared with compressive strength obtained from UCS test to find out the optimum treatment chemical dosage for field application.