## 1 Introduction  
Since the turn of the 21 st century, subway construction has undergone rapid expansion, with the global operating mileage exceeding 21,745.16 km by 2023 [1]. Amidst this growth, the shield method has emerged as the preferred construction technique for subways, attributed to its efficiency, safety, and high mechanization levels. During shield tunneling, modifying shield muck is crucial to maintain the tunnel face pressure stability and enhance tunneling efficiency [2; 3; 4], resulting in substantial amounts of shield tunnel muck. In practical projects, the accumulation and transportation of this regulated muck pose significant environmental hazards and economic burdens [5; 6; 7; 8], potentially triggering disasters like landslides [9]. Hence, proper disposal is imperative. Effective recycling of shield muck can mitigate these issues and promote sustainable resource development [6; 10]. However, current utilization rates remain unsatisfactory. For instance, China annually produces approximately 119 million tons of shield muck, yet the actual effective utilization rate falls below 1% [11]. Consequently, exploring efficient utilization strategies for shield muck holds great significance. The much generated from shield construction, upon undergoing secondary treatment, can be versatilely applied in various fields, encompassing road base filling [12], structural concrete [13], controlled low-strength material (CLSM) [14; 15; 16; 17], construction materials [18], concrete aggregates [19], unfired bricks [20; 21], gardening soil amendment [22], and ceramsite production [23], among others. Although these treatments elevate much utilization, they necessitate transporting the much to designated facilities, thereby augmenting transportation expenses and environmental risks. The application potential for the direct utilization of silt in shield construction is extremely broad [8]. During shield tunneling, substantial synchronous grouting is necessary to manage stratum settlement, ensure tunnel structural stability, and improve waterproofing [24; 25; 26; 27]. Notably, the muck discharged can undergo minimal treatment and be directly utilized as the base material for synchronous grouting, particularly in the form of single-phase slurries (typically comprising cement, bentonite, fly flash, sand, water, and additives). This approach streamlines the treatment process, significantly curtailing transportation and treatment costs. Moreover, implementing this scheme onsite negates the need for external muck transportation, offering operational convenience and economic benefits. The focus of research on slurry performance enhancement through muck primarily revolves around sandy and clay muck. In sandy stratum, the shield excavation generates sandy muck, which often substitutes sand in synchronous grouting processes [28; 29; 30]. Conversely, when tunneling through clay stratum, clay muck typically replaces bentonite in the grouting mixture [31; 32; 33; 34; 35; 36]. Several studies have examined the effects of slurry parameters like the ratio, content, injection quality, and diffusion time on slurry characteristics in clay stratum [34; 37]. However, most of these studies isolate individual factors, neglecting that the performance of synchronous grouting slurry is a holistic outcome of intricate chemical interactions among mixed raw materials [38]. As a result, a comprehensive evaluation of slurry performance under multiple-factor interactions remains inadequate. Moreover, few practical project instances exist where clay stratum shield tunnel muck is reused in lieu of bentonite. Thus, to bolster the practicality and reliability of this substitution, further investigation is vital. In this paper, based on a practical project, the project concerning the substitution of bentonite with silty clay and muck generated during shield tunneling as the raw material for simultaneous grouting slurry is investigated.