This study aims to address the challenge of backfill compaction in the confined spaces of municipal utility tunnel trenches and to develop an environmentally friendly, zero-cement-based backfill material. The research focuses on the excavation slag soil from a utility tunnel project in Handan. An alkali-activated industrial-solid-waste-excavated slag-soil-based controllable low-strength material (CLSM) was developed, using NaOH as the activator, a slag-fly ash composite system as the binder, and steel slag-excavated slag as the fine aggregate. The effects of the water-to-solid ratio (0.40-0.45) and the binder-to-sand ratio (0.20-0.40) on CLSM fluidity were studied to determine optimal values for these parameters. Additionally, the influence of excavated soil content (45-65%), slag content (30-70%), and NaOH content (1-5%) on fluidity (flowability and bleeding rate) and mechanical properties (3-day, 7-day, and 28-day unconfined compressive strength (UCS)) was investigated. The results showed that when the water-to-solid ratio is 0.445 and the binder-to-sand ratio is 0.30, the material meets both experimental and practical requirements. CLSM fluidity was mainly influenced by the excavated soil and slag contents, while NaOH content had minimal effect. The unconfined compressive strength at different curing ages was negatively correlated with the excavated soil content, while it was positively correlated with slag and NaOH content. Based on these findings, the preparation of zero-cement CLSM using industrial solid waste and excavation slag is feasible. For trench backfill projects, a mix of 50-60% excavated soil, 40-60% slag, and 3-5% NaOH is recommended for optimal engineering performance. CLSM is a new type of green backfill material that uses excavated soil and industrial solid waste to prepare alkali-activated materials. It can effectively increase the amount of excavated soil and alleviate energy consumption. This is conducive to the reuse of resources, environmental protection, and sustainable development.

This study evaluated the performance of cement-based grouts in compaction grouting. In the experimental study carried out, the simultaneous effects of fly ash (FA) and nano-silica (NS) on rheological and fresh-state as well as strength performances were investigated. In this context, 16 samples were prepared using 0%, 10%, 20%, and 30% FA replacement levels and 0%, 1%, 2%, and 3% NS content ratios at w/b = 0.75. Rheological characteristics and behavioral performance were defined with shear stress, apparent viscosity, yield stress, and plastic viscosity. Fresh-state performances, flow time with mini-slump, stability capacity with bleeding, and hardening periods with setting time were determined. In terms of mechanical performance, 28-day unconfined compressive strength (UCS) tests were carried out on grout samples. After the tests, the correlation relationship between them was examined using experimental data. The experimental results were performed with statistical analysis, and then, the contribution and impact levels of important parameters were evaluated. Test results showed that the simultaneous FA and NS influence resulted in reasonable outcomes in both the rheological and fluidity properties and caused a visible enhancement in the strength features., Statistically, NS content was dominant in rheological and fresh-state performance, while FA replacement was effective in strength features.