Influence of drying–wetting cycles on soil-water characteristic curve of undisturbed granite residual soils and microstructure mechanism by nuclear magnetic resonance (NMR) spin-spin relaxation time (T₂) relaxometry

Abstract

Due to the formational environment and climatic variability, granite residual soils with grain-size distribution ranging from gravel to clay undergo multiple drying–wetting cycles. The influences of multiple drying–wetting cycles on the soil-water characteristic curve (SWCC) and pore-size distribution (POSD) of undisturbed granite residual soils are investigated using the pressure plate test and nuclear magnetic resonance (NMR) spin-spin relaxation time (T2) distribution measurement, respectively. Results show that the water-retention capacity and air-entry value decrease and pores become more uniform with increasing drying–wetting cycles. After four drying–wetting cycles, the soil reaches a nearly constant state. The POSD change of multiple drying–wetting cycle samples is consistent with the SWCC of the soils. Furthermore, a modified van Genuchten model in terms of cumulative pore volume is used to obtain the best-fit POSD of the drying–wetting cycle samples. The shape and changing tendency of both curves of SWCC and POSD are quite similar and achieved a better correlation. It can be concluded that the SWCC is strongly dependent on the POSD of the soil and NMR T2 relaxometry can be used as an alternative to the assessment of microstructural variation of residual soils subjected to the periodic drying and wetting process.

Effect of Wetting‐Drying Cycles on Mechanical Behaviour and Electrical Resistivity of Unsaturated Subgrade Soil

“…e EMC was set as 17% in the test, and the cyclic amplitude of wetting-drying was considered as EMC ± 1%, EMC ± 3%, and EMC ± 5%. Since 2 Advances in Civil Engineering many studies [10,15,29,30] have reported that the in uence of wetting-drying cycles on the properties of soil is limited after 4 to 6 cycles, the maximum number of wetting-dryings was selected as ve cycles in this study. After each wettingdrying cycle, the dimensions of the specimen should be measured to calculate volumetric strain of specimens.…”

“…Wetting-drying cycles can be treated as an alternative loading on the soil in form of suction along with the change of moisture content. So, the soil-water characteristic or hydromechanical behaviour is also studied [1,9,10]. e initial condition and suction path can affect the properties of soil subjected to cyclic wetting-dryings.…”

Permeability Evaluation of Clay-quartz Mixtures Based on Low-Field NMR and Fractal Analysis

“…The time τ was equal to half of echo time. The CPMG pulse sequence used in this study was same as that in previously studies [43,[53][54][55]. It was testified the CPMG pulse sequence could be used to determine the value of T 2 of soil samples.…”

A New Soil-Water Characteristic Curve Model for Unsaturated Loess Based on Wetting-Induced Pore Deformation

“…Much research has been conducted on the theoretical model of the SWCC. According to some studies, the SWCC is influenced by multiple factors, including temperature [37], drying and watering cycles [38][39][40], stress history [41,42], and initial density [43][44][45], in which the pore structure of the soil has a decisive influence on the SWCC [46][47][48][49]. Early SWCC models used the pore distribution coefficient to reflect the influence of the pore structure.…”