38 research outputs found
Effect of particle size on the measurement of the apparent contact angle in sand of varying wettability under air-dried conditions
Session: Advances in Experimental Methods: Mechanical PropertiesChanges in the wettability of soil are known to affect several processes such as infiltration and the shear strength of soil. In this study, the wettability of a medium to fine sand was chemically modified by using different concentrations of dimethyldichlorosilane (DMDCS). The sessile drop method (SDM) was used for the assessment of wettability of hydrophobised Leighton Buzzard Sand (LBS). The results demonstrate that beyond a concentration of 2 g per kg of LBS, the finer fraction had its apparent contact angle (ACA) increased up to 115° while the maximum ACA attained by the coarser fractions was 100°. At such high concentration of DMDCS, the effect of trapped air, which is known to increase the ACA, was found to be either small or insignificant. The standard deviations of the ACAs agreed well with past studies. The most important factors contributing to the water-repellent behaviour of chemically synthesised sand were attributed to the characteristics of the particles; these include surface area and particle shape.published_or_final_versio
Testing surfactants as additives for clay improvement: compaction and suction effects
Environmental Geotechnics (Joint TC106-TC215 Session)This paper presents an exploratory study on surfactants as additives to improve soil properties. It is hypothesized that surfactant molecules populate the air-water interfaces reducing surface tension and suction thus allowing a control of the mechanical response of the soil. Suction measurements by means of a high suction tensiometer, compaction tests and Atterberg limits were conducted in mixtures of sand and kaolin, with and without a surfactant solution. The results revealed a prominent effect on suction, but to a lesser extent on the Atterberg limits and compaction behavior (the maximum dry density). This targeted effect of the surfactants suggests its molecules populate, not only the air-water interfaces decreasing surface tension, but may be adsorbing to the clay particles and forming micelles in the pore water as well. Therefore the interplay between the three may influence the soil behavior.published_or_final_versio
Challenges in monitoring and managing engineered slopes in a changing climate
Geotechnical asset owners need to know which parts of their asset network are vulnerable to climate
change induced failure in order to optimise future investment. Protecting these vulnerable slopes requires monitoring
systems capable of identifying and alerting to asset operators changes in the internal conditions that precede failure.
Current monitoring systems are heavily reliant on point sensors which can be difficult to interpret across slope scale.
This paper presents challenges to producing such a system and research being carried out to address some of these
using electrical resistance tomography (ERT). Experimental results show that whilst it is possible to measure soil
water content indirectly via resistivity the relationship between resistivity and water content will change over time for
a given slope. If geotechnical parameters such as pore water pressure are to be estimated using this method then ERT
systems will require integrating with more conventional geotechnical instrumentation to ensure correct representative
information is provided. The paper also presents examples of how such data can be processed and communicated to
asset owners for the purposes of asset management
Stress dependent thermal pressurization of a fluid-saturated rock
Temperature increase in saturated porous materials under undrained conditions
leads to thermal pressurization of the pore fluid due to the discrepancy
between the thermal expansion coefficients of the pore fluid and of the solid
matrix. This increase in the pore fluid pressure induces a reduction of the
effective mean stress and can lead to shear failure or hydraulic fracturing.
The equations governing the phenomenon of thermal pressurization are presented
and this phenomenon is studied experimentally for a saturated granular rock in
an undrained heating test under constant isotropic stress. Careful analysis of
the effect of mechanical and thermal deformation of the drainage and pressure
measurement system is performed and a correction of the measured pore pressure
is introduced. The test results are modelled using a non-linear
thermo-poro-elastic constitutive model of the granular rock with emphasis on
the stress-dependent character of the rock compressibility. The effects of
stress and temperature on thermal pressurization observed in the tests are
correctly reproduced by the model
Influence of effective stress on swelling pressure of expansive soils
The volume change and shear strength behaviour of soils are controlled by the effective stress. Recent advances in unsaturated soil mechanics have shown that the effective stress as applicable to unsaturated soils is equal to the difference between the externally applied stress and the suction stress. The latter can be established based on the soil-water characteristic curve (SWCC) of the soil. In the present study, the evolution of swelling pressure in compacted bentonite-sand mixtures was investigated. Comparisons were made between magnitudes of applied suction, suction stress, and swelling pressure