The California Bearing Ratio and Pore Structure Characteristics of Weakly Expansive Soil in Frozen Areas

Tianguo Li,Bingheng Liu,Lingwei Kong

doi:10.3390/app10217576

Abstract

The California Bearing Ratio (CBR) of weakly expansive soil is specially relevant to its expansibility. The mechanisms affecting the bearing strength, in terms of the CBR, of weakly expansive soil that could be used as embankments filler are worth studying. In the present study, the effects of compaction energy on the compaction characteristics and CBR value were investigated. Additionally, the pore size distributions of soils with different compaction degrees were studied with nuclear magnetic resonance (NMR), and the effect of freeze–thaw cycles on the pore size distribution of soils with different compaction degrees was considered. Subsequently, the mechanisms influencing the CBR were analyzed at both the macroscale and microscale. A linear relationship between the CBR value and compaction degree was determined, characterizing the gradual variation of expansive soils with different moisture contents. With increasing freeze–thaw cycles, the volume of micropores decreased and mesopores increased, causing the CBR value to decrease. The expansion was a dominant factor for the CBR values. The CBR values rose with an increase in micropores and decreased with an increase in pore volume. It was considered that the tested weakly expansive soil could be used as an embankment filler in frozen areas.

Highlights

Compaction is considered as a technique for improving the engineering properties of soils, which reduces their permeability and increases their strength [1]
Nuclear magnetic resonance refers to a technology in which the nuclear spin in the low-energy state transitions to a high-energy state by absorbing the energy provided by a radio frequency (RF) field, and the energy change of the nucleus in the magnetic field provides information regarding the nucleus
The results revealed that the California Bearing Ratio (CBR) value decreased with an increasing number of freeze–thaw cycles, as shown in it is indicated that the freeze–thaw cycles could cause a loss of strength, while the CBR

Summary

Introduction

Compaction is considered as a technique for improving the engineering properties of soils, which reduces their permeability and increases their strength [1]. Under a given compaction energy, the relationship between the moisture content and dry density (the compaction curve) can be used to represent the compaction characteristics of the soils. The abscissa and ordinate of the peak point of the compaction curve represent the optimal moisture content and maximum dry density, respectively. NMR technology was used to investigate the pore characteristics of the compacted expansive soil instead of the more common mercury intrusion porosimetry (MIP). NMR can test large-sized samples of 60 mm × Φ60 mm and does not damage the soil It is capable of measuring the same sample multiple times, reflecting continuous changes in the sample’s microstructure. The peak area below the distribution curve represents the nuclear signal corresponding to the T2 range, i.e., moisture content [30,31]

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