Influences of Drying and Wetting Cycles and Compaction Degree on Strength of Yudong Silt for Subgrade and Its Prediction

Hindawi Advances in Civil Engineering Volume 2018, Article ID 1364186, 10 pages https://doi.org/10.1155/2018/1364186 Research Article Influences of Drying and Wetting Cycles and Compaction Degree on Strength of Yudong Silt for Subgrade and Its Prediction Junran Zhang ,1 Tong Jiang ,1 Xingcui Wang,1 Chong Liu,2 and Zhiquan Huang1 1 Henan Province Key Laboratory of Geomechanics and Structural Engineering, North China University of Water Resources and Electric Power, Zhengzhou, Henan 450045, China 2 College of Civil Engineering and Architecture, Guangxi University, No. 100 of University East Road, Nanning, Guangxi 530004, China Correspondence should be addressed to Tong Jiang; Received 5 February 2018; Revised 7 April 2018; Accepted 6 May 2018; Published 22 July 2018 Academic Editor: Yonggui Chen Copyright © 2018 Junran Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In order to investigate the influences of drying and wetting cycles, initial degree of compaction, and water content on shear strength of the Yudong subgrade silt, a series of direct shear tests were performed at saturated and unsaturated states. The test results show that effects of the drying and wetting cycles, water content, and compaction degree on cohesion are more evident than those on the internal friction angle. According to the test data, a formula for the cohesion was proposed, which accounts for the drying and wetting cycles, water content, and degree of compaction. Because Bishop’s strength formula for unsaturated soils could not be applied to Yudong silt, a formula is given based on Fredlund’s formula for predicting the shear strength of unsaturated Yudong silt from the soil-water characteristic curve. 1. Introduction The silt distributes widely on the Yellow River alluvial plain in the eastern Henan province (referred to as Yudong) and thus is often used as a road subgrade or fill material. Yudong silt has a high content of silt-size particles, and the silt-size particles do not bond very well in drying state and are easily crushed. However, it is sensitive to water and easily becomes liquefaction alike, which means that it has poor engineering stability as a road building material. The soils in nature are subjected to climate change and undergo periodical drying and wetting cycles. The drying and wetting cycles can significantly alter the hydromechanical behavior of soil and damage earth structures [1]. In the natural environment, there are changes in groundwater level and seasonal drying and wetting by evaporation and infiltration of precipitation, respectively, and thus, subgrade soils are subjected to multiple drying and wetting cycles, resulting in deformation and uneven settlement of the subgrade layer, surface crack, and other failures. Because of their importance in engineering applications, the effect of drying and wetting cycles and water content on the shear strength of silt needs to be considered. In recent years, there have been many studies on the effect of drying and wetting cycles on soil strength. A literature review on hydraulic cycles shows that several dryingwetting cycles [2–4] produce an equilibrium state after which the soil exhibits elastic behavior. Moreover, the irreversible volumetric deformation during the drying and wetting cycles was found to be the function of compaction conditions and the subsequent variation of stress/hydration paths [5, 6]. Goh et al. [7] showed that the shear strength characteristics of soils under the drying and wetting cycles are different. Zhang et al. [8] and Sun et al. [9] showed that even if the same path of net stress and suction was followed during triaxial shearing, the stress-strain and strength behavior are different between specimens experiencing different suction histories. After experiencing a larger suction, the void ratio decreases significantly, and thus, the specimen exhibits the deformation characteristics similar to the overconsolidated clay during shearing [10]. The effect of 2 Advances in Civil Engineering Table 1: Basic physical properties of Yudong silt. Specific gravity (Gs) 2.72 Liquid limit, wL (%) Plastic limit, wp (%) Plasticity index, Ip Maximum dry density, ρd (g/cm3) Optimum water content, wopt (%) 24.5 17.3 7.2 1.72 12.7 1.74 1.72 80 1.70 60 ρd (g/cm3) Percentage passing (%) 100 40 1.68 1.66 1.64 20 1.62 0 100 10–1 10–2 Particle size (mm) 10–3 1.60 8 10 12 14 16 18 w (%) Figure 1: Grading curve of Yudong silt. Figure 2: Compaction curve of Yudong silt. hydraulic hysteresis on shear strength of unsaturated clay was studied by Chiu et al. [11]. Nowamooz et al. [12] developed an effective stress parameter to assess the cyclic behavior of swelling soils in drying and wetting cycles. Several studies have been conducted to assess the effect of drying and wetting cycles on hydraulic conductivity, and the swelling capacity of clay barriers by using different methods [13–18]. In summary, the influence of drying and wetting cycles on mechanical properties of soils is obvious, and the study on silty soil is less compared with expansive soils. The soil-water characteristic curve (SWCC) plays a key role in unsaturated soil mechanics. Measurement of the SWCC is expensive and time consuming and requires special technique or equipment in laboratory. Sun et al. [19–22] studied the affecting factors of the SWCC by results of the pressure plate tests and concluded that the direct affecting factor is the void ratio rather than the stress or stress history. Gallage and Uchimura [23] studied the effects of dry density and grain size distribution on the SWCC of sandy soils. Gao and Sun [24] studied the soil-water retention behavior of compacted soil with different densities over a wide suction range. Zhou and Sheng [25] proposed an advanced hydromechanical constitutive model for unsaturated soils with different initial densities considering the changes of the SWCC. Ho et al. and Kong et al. [26, 27] studied the SWCCs of granite residual soils experiencing multiple drying and wetting cycles. Zhou [28] proposed a contact angle-dependent model in incremental form to reproduce the soil-water hysteresis behavior. From the above discussion, it can be seen that the effects of the void ratio and drying and wetting cycles on the SWCC are significant, and the quantitative relationship between them can help us to predict the strength of unsaturated soils with the SWCC. The effects of drying and wetting cycles and water content on the soil strength have been well documented, but to date, few scholars have reported how drying and wetting cycles affect the strength of Yudong silt, which are not fully understood. Besides, the silt is formed by alluvial deposits of the Yellow River, and it has a special geological condition and mainly contains silt-size p (...truncated)