Research on the Reuse of Discharged Soil from EBP Shield Tunnels in Synchronous Grouting Material

Great practical significance and engineering application value can be achieved when the large amount of discharged soil produced by EPB shield tunnels is recycled and comprehensively utilized. As one of the key processes of shield construction, synchronous grouting needs a large amount of bentonite, cement, fly ash, sand, and other materials. The research on the reuse of shield muck as synchronous grouting material is carried out based on Zhengzhou subway project. The physical properties and phase of the discharged soil from EPB shield tunnels are studied by using laboratory tests and XRD. The statistics show that the shield muck meets the performance requirements of bentonite and fine sand in synchronous grouting materials. The optimal grout ratio of the reused muck is obtained based on the optimization idea of multiobjective programming by MATLAB. Considering the combined effect of seepage field, stress field, and the timeliness of the grout, the influences of grouting pressure and the filling rate of synchronous grouting on surface settlement, plastic zone of strata, and segment deformation are analyzed by using finite difference method. The results prove that the surface settlement and segment deformation can be better controlled when the grouting pressure is at 0.18 MPa and the grouting rate is at 120%–150%.

Assessment of the Influence of the Type of Filler Materials on the Properties of Cement Grouts

Cement grouts have many purposes in various civil engineering applications such as precast construction, soil stabilization and structural rehabilitation. Using filler materials as a component in cement grouts has been increasingly implemented. The incorporation of such fillers not only does improve the fresh and hardened properties of grouts but also contributes to the decarbonization of grouts by reducing the amount of Portland cement, thereby lowering the carbon footprint of grouting materials. This study aims at assessing the influence of various filler materials on the properties of cement grouts. Three different fillers were used in this study: commercial limestone, commercial pure dolomite, dolomitic quarry dust. These fillers were assessed in terms of their effect on the spread, flowability, cohesion and compressive strength at 3, 7 and 28 days. The results show that fresh properties of the grout were dependent on the type of fillers. Dolomitic quarry dust improved the workability and flowability more than the commercial limestone and dolomite did. The compressive strengths of cement grouts did not change significantly with the incorporation of the fillers. However, cement grout samples including quarry dust exhibited slightly higher 28-d compressive strength than other samples although the same mix had lower 1-d compressive strength than other mixes. This study highlights the benefits of utilizing quarry dust in cement-based binders without compromising the performance.

Optimization of Grouting Material Mixture Ratio Based on Multi-Objective Optimization and Multi-Attribute Decision-Making

As a solid waste produced by coal combustion, fly ash will cause serious environmental pollution. However, it can be considered as a sustainable and renewable resource to replace partial cement in grouting materials. Fly ash grouting materials re-cement the broken rock mass and improve the mechanical properties of the original structure. It can reinforce the broken surrounding rock of mine roadway. The utilization of fly ash also reduces environmental pollution. Therefore, this paper establishes a new material mixture ratio optimization model to meet the requirement of material property through combining the methods of experimental design and numerical analysis. Based on the Box–Behnken design with 3 factors and 3 levels, a mathematical model is constructed to fit the nonlinear multiple regression functions between material properties and raw materials ratios. The influence of raw materials is analyzed on material properties (the material’s 7-day uniaxial compressive strength, initial setting time, and slurry viscosity). Then, 80 Pareto solutions are obtained through NASG-II algorithm which takes the regression functions as the objective functions for multi-objective optimization of the grouting material ratio. Finally, the best ratio solution of water-cement ratio—0.71, silica fume content—1.73%, and sodium silicate content—2.61% is obtained through the NNRP-TOPSIS method.

Mosul Dam, NW Iraq: Is a Safe Dam??

Mosul Dam is located in the northwestern part of Iraq impounding the Tigris River; about 60 km north of Mosul city. This project is multipurpose project; to provide water for irrigation, flood control and hydropower generation. The dam is 113 m high and 3650 m long including the spillway. The dam is earth fill type with a mud core. The dam was designed to impound 11.11 km3 because it is based and underlain by gypsum beds alternated with limestone and marl. Therefore, it is planned to use continuous grouting to fill the karst caverns. The used quantity exceeded 95000 tons of solid grouting materials since 1986 up to 2014. After all, is the dam safe? The details are given in the current article.

Tests Research on Grouting Materials of Waste-Concrete-Powder Cement for Goaf Ground Improvement

Waste concrete powder (WCP) is proposed to replace part of the cement to seek environmentally friendly grouting materials for ground improvement in mine goaf. The optimal mixing proportion was selected based on the performance indexes of the water-separation ratio, stone rate, viscosity, setting time, and compressive strength. X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were also conducted to analyze mineralogical phases and investigate the microscopic mechanism. Test results show that the slurry prepared by the substitution rate of 70% and adding 0.05% water-reducing agent meets well the requirements of ground grouting in mine goaf. The WCP produced by grinding mainly exerts microaggregate effect in the slurry due to low activity. A lot of pores on the surface of WCP were shown by SEM which can absorb the water in the slurry and increase the stone rate. The WCP application for ground grouting in mine goaf can not only recycle WC but also provide new grouting materials for goaf ground.

Study of Rheological Properties of Carbon Nanotube-Reinforced Ultrafine Cement Grouting Materials

In this study, three different diameters of multi-walled carbon nanotubes (MWCNTs) dispersed by polyvinyl pyrrolidone (PVP) were used to reinforce superfine cement grouting materials. The effect of MWCNTs and polyvinyl pyrrolidone (PVP) on the rheological properties of grouting material were accordingly studied. It was found that the yield stress (τ0) and plastic viscosity (η) were slightly decreased when PVP content was low and increased when the PVP content increased. The effect of MWCNT diameter on τ0 was not found to be clear but was more significant on η. The smaller MWCNT diameter was, the more quickly η increase. It was also found that the thixotropic ring area was increased as the MWCNTs content increased. The addition of PVP and MWCNTs caused an increase in the number of entanglement points in different scales, which was the main reason for the viscosity and thixotropy increase. Therefore, the rheological properties of superfine cement grouting material should be adjusted when MWCNTs were added as a reinforcing component. Due to the wrapping of PVP on cement particles which isolates the contacting part between the water and the cement particles, it slows down the cement's hydration rate thus slows down the fluidity loss of the slurry.

Grouting technology and construction schemes of a tunnel in aeolian stratum: a case study of Shenmu No. 1 tunnel

The naturally formed aeolian sand dunes in northern Shaanxi exhibit unique engineering characteristics. Several challenges, such as the poor self-stabilization ability of the surrounding rock, difficultly in injecting grout, and insufficient construction experience, restrict the construction of road tunnels under this stratum. Therefore, in this study, a case study of the Shenmu No. 1 tunnel was conducted to investigate the engineering characteristics of aeolian sand tunnels, compare the grouting effects of commonly used grouting materials, and discuss the reinforcement effects of different construction schemes in aeolian sand tunnels. Based on a field grouting test, it was determined that it is difficult to inject ordinary cement grout into an aeolian sand layer. Furthermore, it was determined that superfine cement grout and modified sodium silicate grout can be injected, but the former exhibits a poor reinforcement effect. Additionally, results of numerical analysis indicated that an approach based on a concept of “horizontal jet grouting pile + benching partial excavation method with a temporary invert” is suitable for the construction of tunnels in aeolian sand in China.