Shear Strength Deterioration of Compacted Residual Soils under a Wind Turbine due to Drying‐Wetting Cycles and Vibrations

Abstract

The soil beneath a wind turbine withstands not only environmental impacts but also continuous vibrations transmitted from the superstructure. This paper presents an experimental study of the deterioration characteristics of shear strengths of residual soils affected by drying-wetting cycles and continuous vibrations. A series of triaxial tests were performed on compacted residual soil specimens after various drying-wetting cycles and vibrations. The influences of drying-wetting cycles and vibrations on the shear strengths of residual soils with different compaction degrees were analyzed. The results demonstrate that the shear strength and cohesion of compacted residual soils decreased as the number of drying-wetting cycles increased, and they tended to be stable after three drying-wetting cycles. The angle of internal friction decreased linearly with the reduction of compaction degree but was generally not affected by drying-wetting cycles. The shear strength of compacted residual soils also decreased because of continuous vibrations. After 10000 vibrations, the strength was stabilized gradually. Both the cohesion and angle of internal friction showed dynamic attenuation phenomenon. Finally, a modified Mohr–Coulomb strength equation considering the effects of drying-wetting cycles and vibrations was established. This equation could be used to predict the shear strength of compacted residual soils and further estimate the embedded depth of wind turbine foundations.

Evolution of Soil Pore Structure and Shear Strength Deterioration of Compacted Soil under Controlled Wetting and Drying Cycles

“…The significant shrinkage of macro-pores primarily causes this, while the micro-pores remain unchanged or slightly increase [35]. Repeated wetting and drying cycles result in cumulative deterioration within the soil, leading to the broadening enlargement of localised weak zones, characterised by developing cracks at the mesoscopic scale [36]. This is confirmed by X-ray CT analysis of soil samples subjected to increasing wetting and drying cycles in this study.…”

“…Fewer studies have been reported on the drained/effective shear strength of soil influenced by wetting and drying cycles, and contradictory findings are present in the literature. For instance, Zhou et al [36] found that the internal friction angle fluctuates within a narrow range, while the reduction in cohesion is the primary cause of shear strength degradation during wd cycles. Zhu et al [39] and Khan et al [9] reported a decrease in both cohesion and angle of internal friction of soil with wd cycles for expansive soils.…”

Effect of Drying–Wetting Cycle and Vibration on Strength Properties of Granite Residual Soil

“…Since a vibration test can quantitatively control parameters such as vibration time, this method is more used for disturbance research. Commonly used vibration methods include the shaking table [23,24], the GDS dynamic triaxial instrument [25,26] and the vibrating sieve machine [27,28]. These methods destroy the original structure between soil particles through vibration and obtain disturbed samples.…”