Influence of Degree of Compaction on Unsaturated Hydraulic Properties of a Compacted Completely Decomposed Granite

Rui Chen,Runqiang Tan,Yang Ping,Zhongkui Chen,Zhen Mei

doi:10.1155/2020/7615361

Abstract

It is crucial to understand hydraulic properties, i.e., soil-water characteristic curve (SWCC) and unsaturated permeability function (UPF), of completely decomposed granite (CDG) for relevant engineering projects in southeastern China. Previous studies mainly focused on SWCCs of CDG, whereas UPFs of CDG have not yet been well understood. In this study, the effects of the degree of compaction (DOC) on SWCCs and UPFs of CDG were investigated based on experiments where suction range was from 0 to 500 kPa. The microstructure of soil specimens was then analyzed by mercury intrusion porosimetry (MIP). Furthermore, the UPFs of CDG under different values of DOC were calculated using four prediction models and compared with experimental data. Results showed that the pore volume of specimens at higher DOC was smaller than that at lower DOC, and there were more macropores observed in specimens at lower DOC. Meanwhile, it was found that increasing compaction effort produced negligible influence on the volume of micropores. When the suction was less than 100 kPa, the permeability was reduced with the increase in DOC, due to the decrease of macropore volume. However, the influence of DOC on SWCCs and UPFs became marginal when the suction exceeded 100 kPa. The Fredlund and Xing model provided the best prediction of UPF among the four models when suction was smaller than air entry value (AEV). It is suggested that these models could be improved to capture UPFs at higher suctions than AEV by considering suction-induced volume contraction.

Highlights

In the southeastern coastal area of China, completely decomposed granite (CDG) with thicknesses up to 50 m is widely distributed on the gentle hills and terraces
Four models proposed by Gardner, Brooks and Corey, van Genuchten, and Fredlund and Xing [9,10,11,12] were used to predict the unsaturated permeability function (UPF) of CDG at different values of degrees of compaction (DOC)
The following conclusions were drawn: (1) The influence of DOC on soil-water characteristic curve (SWCC) and UPFs of CDG was of great significance within the suction of 100 kPa, whereas the influence became marginal when the suction exceeded 100 kPa

Summary

Introduction

In the southeastern coastal area of China, completely decomposed granite (CDG) with thicknesses up to 50 m is widely distributed on the gentle hills and terraces. Evaporation causes the reduction of soil water content, resulting in the change of hydraulic properties, i.e., soil-water characteristic curve (SWCC) and unsaturated permeability function (UPF) [1, 2], of CDG in the tropical and subtropical areas such as southeastern China. Tang et al [3] used the osmotic method to obtain drying and wetting SWCCs of CDG They found that both desorption and absorption rates of SWCC were relatively small and the air entry value (AEV) was only about 10 kPa. Chen and Gong [4] studied the effect of initial dry density on SWCCs of CDG using the filter paper method and concluded that increasing initial dry density caused an increase in the AEV but a decrease in the desorption rate. Yin [5] measured the saturated permeability coefficients of CDG under different degrees of compaction (DOC) by fallinghead permeability tests and found that with the increase in DOC, the saturated permeability coefficient decreased linearly in a semilogarithmic coordinate system

Objectives

Methods

Results

Conclusion