Cone Penetration Test in Unsaturated Soil with Matric Suction Measurement
Wong, Jonathan 1991-
This research consists of two main studies. In the first half of this dissertation, the research findings regarding the use of 3D scanner for shrinkage limit testing of soils are presented; the second half of this dissertation presents the findings related to the chamber tests conducted which measures the matric suction of the unsaturated soil during cone penetration tests. Part I: Shrinkage curve Evaluation using a 3D scanner A procedure is proposed for conducting shrinkage limit tests using a 3D scanner. Shrinkage limit tests were conducted on 13 different soils of various plasticity. Shrinkage curves for each material were obtained by curve fitting a shrinkage model to the measured dataset. Using linear regression analysis, an empirical correlation was developed to reasonably relate parameter csh from the shrinkage model to the ratio of the plastic and liquid limits. The shrinkage curves produced based on the model have an average difference of ~1.2% in terms of measured void ratio and predicted void ratio. The method was demonstrated to be robust for materials of low, medium, and high plasticity. The proposed methodology also presents a means of estimating a shrinkage curve in its entirety based solely on the volume of an air-dried sample, the specific gravity and Atterberg limits of the specimen. This effectively reduces the amount of work needed to derive the shrinkage curve and could potentially reduce the time for a shrinkage limit test by half or more. Part II: Cone Penetration Testing in Unsaturated Silt with Matric Suction measurements Most empirical correlations used to interpret cone penetration test (CPT) results have been developed from and for saturated soils, so the applicability of CPTs to unsaturated soils remains in question. This paper presents experimental results for CPTs conducted in a chamber instrumented with four rapid-response tensiometers and filled with an unsaturated silt: one test with silt at one water content and three tests with two layers of silt at different water contents (drier layer overlying the wetter layer). Two pore pressure dissipation (PPD) tests were conducted after 400 to 500 mm penetration in each layer. Negative pore-water pressures (matric suction) were monitored during advancement of the cone and the PPD tests; cone resistance, sleeve friction, and pore-water pressure were also recorded. CPT results indicate the built-in pore-water pressure transducer cannot provide useful information regarding pore pressure and hydraulic properties of the unsaturated soil. Hence, tensiometers ought to be used to obtain pore pressure measurements during and after penetration. Tensiometer readings can also be used to characterize the unsaturated soil in terms of the in situ soil water characteristic curve (SWCC), unsaturated hydraulic conductivity, in situ pore-water pressure profile, and in situ effective stress. Existing empirical correlations used to interpret the results of PPD tests and soil behaviour type (SBT) are reviewed. Using a spherical cavity expansion solution, a method is proposed to estimate the frictional parameters of the unsaturated silt.
DegreeMaster of Science (M.Sc.)
DepartmentCivil and Geological Engineering
CommitteeHawkes, Chris; Ferguson, Grant; Si, Bing
Copyright DateAugust 2018
In-situ testing, unsaturated soil, cone penetration testing