Layered Grouting Technology Based on a Comprehensive Water‐to‐Cement Ratio for the Overlying Loess Stratum of Urban Shallow Tunnels

Abstract

Different from sand and clay, loess has special engineering properties; hence, existing soil grouting theories are not suitable for the disaster treatment of shallow loess tunnels. In this study, a fine grouting reinforcement test system was developed, and the Yuhan Road tunnel overlying loess was used as the injection medium. An orthogonal test based on slurry dry density, moisture content, water-to-cement ratio, and grouting pressure was conducted. Results revealed that the loess samples have high integrity after grouting, and the cohesion and compressive strength improved significantly. The stress-strain curve showed that the strengthened samples have greater ultimate and residual strengths than samples before grouting. Through a range analysis, it was determined that water-to-cement ratio and moisture content are the main factors affecting loess cohesion and compressive strength. Therefore, a comprehensive test of the water-to-cement ratio and moisture content as a single variable was conducted. It was found that their influence on loess cohesion and compressive strength is not a single linear relationship but a combined balance. To characterize the joint effect of water in loess and in slurry on reinforcement, the concept of a comprehensive water-to-cement ratio is proposed, and the cohesion and compressive strength curves with respect to this ratio were drawn. An optimal comprehensive water-to-cement ratio, which corresponds to the maximum cohesion or compressive strength, was found. Based on this ratio, we further propose a method to calculate the water-to-cement ratio of slurry and suitable grouting amount for the Yuhan Road tunnel reinforcement project, in which all solution parameters can be measured via field tests. In the project, a surface layered grouting scheme, based on the optimal comprehensive water-to-cement ratio, was designed. After grouting, loess strength was improved significantly, permeability was reduced greatly, and the overall reinforcement effect was suitable; these results provide a reference for similar projects.

Study on Mechanical Properties of Permeable Polymer Treated Loess

“…The analysis of the effect of grouting under different working conditions shows that the factors influencing the compressive strength of the solidified soil in order are: service environment > water content > dry density. Yang [ 45 ] studied the effects of dry density of loess, water content, water–cement ratio, and grouting pressure on the reinforcement effect, and concluded that water–cement ratio and water content were the main controlling factors. The service environment was introduced in our study.…”

Research on the Experimental System of Reinforcing the Base of Shallow Buried and Wet Collapsible Loess Tunnels

“…Figure 1 shows the longitudinal profile of the tunnel. 2020) established a precise grouting reinforcement test system, using the Yuhang Road tunnel with overlying loess as the injection medium, and conducted an orthogonal test based on slurry dry density, moisture content, water-cement ratio, and grouting pressure [19].…”

“…Fan, H. et al (2023) analyzed the settlement of tunnel bedrock and the structural mechanical response characteristics under the influence of jet grouting piles with different lengths and diameters in weak loess areas using centrifugal model tests, effectively reducing tunnel bottom settlement and significantly shortening the stress adjustment time of surrounding rocks [18]. Yang, T. et al (2020) established a precise grouting reinforcement test system, using the Yuhang Road tunnel with overlying loess as the injection medium, and conducted an orthogonal test based on slurry dry density, moisture content, water-cement ratio, and grouting pressure [19].…”