Wei-lie Zou

Electro-osmotic consolidation of marine hydraulically filled sludge ground using electrically conductive wick drain combined with automated power supply

ABSTRACT Electro-osmosis (EO) methods have not been widely used for the drainage consolidation of soft clay soils in practice because of two key problems; (i) metallic electrode corrosion, and (ii) high electric energy consumption. With recent advancements of conductive plastics, there has been interest in using conductive plastic electrodes instead of metallic electrodes to accelerate drainage of soft clay soils. This paper presents the details of a field EO test using a type of new patented electrically conductive wick drain (ECWD) and a specially designed automated power supply (APS) on a hydraulically filled sludge ground in Jiangsu Province, China. The in-situ investigations and laboratory tests were conducted to evaluate the improvement effectiveness after performing EO treatment for a period of 36 days (including a continuing intermittence of 16 days). The results suggest that the EO technique using the ECWD combined with the APS (i) decreased the average moisture content of the sludge from 62 to 39%; (ii) increased the vane shear strength from ∼0 to 25.5 kPa. In addition, the ground bearing capacity also increased from ∼0 to 74 kPa. The electric energy consumption for this EO treatment is 5.6 kWh/m3. Moreover, the prediction models for electric current I and cumulative drainage Q during EO are validated using data from the present field and laboratory tests. Investigations to date suggest that the new ECWD combined with APS presented in this paper is encouraging for consolidating the large area of soft clay soil with high water content to achieve favourable conditions with respect to increase in shear strength at an acceptable cost.

Mechanical Properties of QH-E Lunar Soil Simulant at Low Confining Stresses

AbstractThe low-moon gravity has a significant influence on the mechanical properties of lunar soils at low-stress levels. To better understand the shear strength and deformation behavior of lunar soils at low confining stress and to facilitate the modeling and simulation of lunar activities, a series of consolidated drained triaxial compression tests were performed on numerous samples of lunar-soil simulant developed by Tsinghua University, China (named as QH-E). Great care was taken to conduct the experimental studies at low confining stresses such that reliable results can be obtained. The measured data suggest that QH-E samples exhibited strain-softening behavior with typical residual shear strength behavior characteristics. It was also found the residual internal friction angle φcs approximately 40°, regardless of confining stress, σ3 and relative density, Dr, whereas the peak apparent cohesion intercept ca−p is not equal to zero owing to the nonlinear behavior of shear strength of QH-E. However, the...

Constitutive Model for Soaking-Induced Volume Change of Unsaturated Compacted Expansive Soil

Several researchers have proposed models extending the independent stress state variables approach to describe the nonlinear nature of the normal consolidation line (NCL) for unsaturated soils. However, there are few models that can describe both the nonlinear nature of the NCL and the non-monotonic variation of collapse potential for unsaturated compacted expansive soils (USCES). In this paper, a constitutive relationship is proposed for the USCES that can be used for interpreting and modeling both the nonlinear NCL and non-monotonic collapse potential by taking account of the influence of macro and microstructure in the term specific volume, υ. In this model, effective degree of saturation, Se is used as one of the state variables, and υ is assumed to linearly decrease with increasing net vertical stress, or mean net stress, when Se is at constant condition. A series of oedometer tests were conducted by soaking the USCES specimens to validate the proposed model. The results of the study suggest that there is a good comparison between the measured data and the prediction curves of NCL during compression using the proposed model. In addition, the model provides excellent predictions of the soaking-induced non-monotonic collapse potential.

Effect of montmorillonite content and sodium chloride solution on the residual swelling pressure of an expansive clay

Expansive clays may continue to swell even after obtaining fully saturated condition due to the continuing montmorillonite hydration process. Expansive clays in this case, if confined, will generate swelling pressure, which is termed as residual swelling pressure in this study. The residual swelling pressure poses significant impact on the long-term safety and stability of adjacent geotechnical infrastructure. Despite its significance, currently, there are very limited studies on the residual swelling pressure. In this paper, the influence of (1) the montmorillonite content and (2) sodium chloride (NaCl) concentration in the pore water on the residual swelling pressure of a compacted expansive clay was evaluated using constant-volume swelling tests. Scanning electron microscopy analyses were applied to investigate the influence of NaCl solution on the microstructure of the compacted expansive clay. Tests results showed that the residual swelling pressure increases with montmorillonite content and dry density of specimen and decreases with an increase in the NaCl concentration. The NaCl in the pore water used for compacting the clay influences the particle orientation and arrangement. High NaCl concentrated solution contributes to soil structures with higher integrity that exhibit lower residual swelling pressure. An equation is developed to interpret and predict the residual swelling pressure of expansive soils considering their montmorillonite content and dry density. The proposed equation is verified using experimental data determined in this study as well as data obtained from the literature.

Experimental Evaluation of Engineering Properties of GFRP Screw Anchors for Anchoring Applications

AbstractSteel screw anchors (SSAs) have been widely used in geotechnical engineering practice because they are simple in structure and easy to design and construct. The main disadvantage of SSAs is that they rust quickly and are not found to be suitable for permanent structures, unless adequate corrosion protection measures are provided. Anchors made of glass fiber–reinforced plastic (GFRP) are corrosion-resistant material that are light in weight with a higher tensile resistance in comparison with SSAs. For this reason, GFRP anchors have been found to be a good substitute for SSAs during the last two decades. In this paper, details of a newly developed GFRP screw anchor (GFRP-SA) with respect to the physicomechanical, tensile, and creep properties along with its performance both in the laboratory and in field conditions are provided. A specially developed machine that facilitates quick installation of the GFRP-SA is also briefly introduced. In addition, two full-scale field tests that were undertaken to ...