Deterioration characteristics of cement-improved loess under dry-wet and freeze-thaw cycles.

Ying-Jun Jiang,Hong-Wei Sha,Zong-Hua Li,Chen-Yang Ni,Lu-Yao Cai,Ahmed Mancy Mosa

doi:10.1371/journal.pone.0253199

Abstract

The effects of cement dosage, compaction coefficient, molding method (vertical vibration method and static pressure method), and dry-wet and freeze-thaw cycles on the mechanical strength of cement-improved loess (CIL) were studied to reveal its strength degradation law under dry-wet and freeze-thaw cycles. Results show that when using the vertical vibration molding method, the strength degradation effect of CIL can be improved by increasing the cement dosage and compaction coefficient; however, it is not obvious. Under the action of dry-wet cycle, damages, such as voids and cracks of CIL, develop continuously. Further, the strength deteriorates continuously and does not decrease after more than 15 dry-wet cycles. Therefore, the dry-wet cycle degradation system is selected by considering the most unfavorable conditions. In the process of freeze-thaw alternation, the pores and fissures of CIL develop and evolve continuously and the strength deteriorates continuously under the joint influence of water and low temperature. The strength tends to become stable after more than 12 freeze-thaw cycles. According to the safety principle, the deterioration coefficient of the freeze-thaw cycles is 0.3.

Highlights

The main engineering problems of loess foundation are large pores, poor cementation, weak shear strength and large deformation under the action of external force
The influence of cement dosage on the strength deterioration of improved loess was studied under the action of the dry–wet and freeze–thaw cycles
The influence of compaction coefficient on the strength deterioration of improved loess was studied under the action of the dry–wet and freeze–thaw cycles

Summary

Introduction

The main engineering problems of loess foundation are large pores, poor cementation, weak shear strength and large deformation under the action of external force. The stress field of the subgrade soil changes and redistributes because of the joint action of temperature, water, and load, resulting in frost heaving, thawing settlement, frost boiling, and other frost damage phenomena These phenomena cause many difficulties in railway engineering [2,3]. Studies to understand the change law of the mechanical properties of loess under the action of dry–wet and freeze–thaw cycles. The above studies mainly focus on the influence of chemical improvement methods and cement content on the resistance of improved loess to dry–wet and freeze–thaw cycles. The strength degradation characteristics of CIL under different cement dosages, compaction coefficients, and dry–wet and freeze–thaw cycles are studied to provide reference for engineering practice. The CIL is pressed to the specified height according to the static pressure method in the code for geotechnical test of railway engineering (TB10102-2010) (hereinafter referred to as the “code”) [22]

Test plan and methods

Dry–wet cycle test

Freeze–thaw cycle test

Conclusion