Cement grouting is widely used in rock tunnelling to control groundwater inflow by sealing rock fractures. Accurately predicting grout propagation in rock fractures is crucial for the design, execution, and monitoring of rock grouting in engineering applications. Current methods rely on theoretical models, such as the real-time grouting control (RTGC) method, which is derived based on simplified fracture geometries like smooth parallel plates/disks. However, real rock fractures consist of rough surfaces with variable apertures. In this study, we present a computational model for theoretically predicting the propagation of non-Newtonian cement grout in variable fracture apertures. This model is validated with laboratory test data on grout propagation in a one-dimensional varying aperture long slot (VALS). We also analysed the impact of varying aperture on cement grout propagation processes. Our findings demonstrate that the presented computational model predicts the grout propagation process in this geometry with good accuracy. Moreover, we observed that varying aperture significantly affects the grout propagation process in fractures. The insights provided by our model and analysis results are potentially useful in rock tunnelling projects, specifically for the theoretical analysis of cement grout propagation in rock fractures. 

In cement-based grouting, insufficient spread of grout within the rock fractures is one of the major issues, which negatively impacts the sealing performance and service life of underground structures. On the other hand, an excess of the grout spread is neither economic nor environmentally friendly. Hence, optimization of the grout spread is of the greatest concern in rock grouting to provide the most reliable and economical solution for sealing in the construction and maintenance of underground facilities. Accordingly, the Real Time Grouting Control (RTGC) theory is a method that has been developed to analyse the spread of grout in rock fractures. It predicts the extent of the grout penetration over time based on grout properties and the applied pressure. Despite extensive work conducted to verify the RTGC method in both the lab and the field, it has not yet been sufficiently investigated in the lab under inhomogeneous geometry conditions like a more realistic rock fracture with variable, non-subsequent apertures.

This investigation therefore took a novel effort to examine the performance of RTGC theory at presence of variable aperture constrictions. The idea is to investigate how close are the results of predictions of grout propagation of RTGC theory (at different aperture orders) with the experimental results obtained using an artificial fracture with adjustable aperture order. A fair comparison is further provided between the predicted results and the results of numerical simulations under different aperture distributions. The predictions are obtained using both the hydraulic aperture, the way that the theory was previously used in the early stages of development, as well as the mean-physical aperture, the way that the theory is currently used in the field applications. 

An unique equipment, referred to as Variable Aperture Long Slot 2 (VALS II), was designed and produced to meet requirements of this investigation. It consists of multiple short aperture plates attached to a 4m long base plate. The aperture plates have different aperture sizes for representing variable apertures in rock fractures and can be mounted on the base plate in any sequence to form desired aperture size distribution with respect to VALS II inlet for grout inflow.

Test results reveal importance of correct evaluation of grout rheology when applying RTGC theory. Based on them it was concluded that if applying fresh grout rheological properties RTGC theory gave not as precise prediction for grout propagation in time as grout rheological properties at 30 minutes from mixing.

This article presents the experimental results from a unique laboratory test-setup used to comparative study of heat transfer conditions in borehole heat exchangers with different grouts under a controlled environment. The work was part of a larger, EU-funded project on advanced materials for borehole heat exchangers pipes and grout, GEOCOND. Four grout columns with different formulations were cast and tested under cyclic heating and cooling. One grout column was cast using high thermal conductivity grout; two columns were cast from high thermal conductivity grout with microencapsulated phase change material (MC-PCM) and one with shape-stabilised phase-change material (SS-PCM). The objective of the test was to comparatively evaluate performance of the borehole heat exchanger under a cyclic temperature regime and to investigate if the selected phase change materials (PCM) embedded in grout can be activated by cyclic heating and function steadily. Twenty-five heating-cooling cycles were performed, each lasted 24 h. The results showed clear cooling delay in grouts containing PCM associated with the crystallization heat release. The cooling delay was better expressed in grouts with SS-PCM. The PCM related cooling delay was stable throughout all the cycling in SS-PCM containing grouts, however, the effect vanished in grouts with MC-PCM. © 2023 The Authors

When it comes to underground structures, water ingress from the surrounding formations leads to several environmental, economic and sustainability issues. To obtain the sealing, the grouting of rock fractures is done. Today, in the grouting operations, which are commonly conducted in almost all the tunnel and subsurface infrastructure projects, the pressure applied is static. This type of applied pressure might be suitable for the large fracture apertures > 100 μm, but it has been acknowledged that it is difficult to obtain sufficient penetration through smaller apertures, where filtration of cement particles starts to occur. Research is already done to overcome this issue by applying dynamic grouting pressure instead of static. It was proved that this approach erodes the formed filter cakes and improves grout penetrability in fractures below 100 μm. This research focuses on low-frequency rectangular pressure impulse as an alternative to other methods. The goal is to improve grout spread in micro-fractures (especially in apertures < 70 μm). During the investigation, a prototype dynamic injection equipment was built and tested under laboratory conditions. The 4 m variable aperture long slot (VALS) was used in the experiments to simulate rock fractures. The test showed better grout penetrability using dynamic pressure approach. At the current time of writing this article, preparation works are done for field test of prototype equipment at SKB Hard Rock Laboratory (HRL) at Äspö, Sweden. 

In this study, a laboratory-scale prototype of a borehole field has been designed and built to assess various innovative grouting products in a fully controlled environment. Three novel grout formulations are developed and evaluated: enhanced grout, a mixture of enhanced grout and microencapsulated phase change material, and a mixture of enhanced grout and shape stabilized phase change material. The objective is to evaluate the enhancement in their thermal properties (i.e., thermal conductivity and thermal energy storage capacity) compared to those using a commercial reference grout. Besides, three-dimensional numerical modeling is performed to provide a better understanding of the heat transfer and phase transition inside and outside the grout columns and to study the capability of the developed grouts to be used in a borehole heat exchanger or as borehole thermal energy storage system. To the best of the authors' knowledge, there have been just a few numerical studies on using phase change materials inside borehole heat exchangers to assess thermal energy storage applications. The experimental and numerical results showed much higher efficiency of the grout developed with a high thermal conductivity than the reference grout in terms of heat transfer in both the grout column and the surrounding sand. Furthermore, the results indicated the noticeable influence of the microencapsulated phase change material's presence in the grout formulation in terms of heat absorption/storage during the phase transition (from solid to liquid). However, it is concluded that reengineering shape stabilized phase change material should be conducted to make it more appropriate for thermal energy storage applications.

In Swedish tunnel construction, a critical issue that has been repeatedly acknowledged is corrosion and, consequently, failure of the rock bolts in rock support systems. The defective installation of rock bolts results in the formation of cavities in the cement mortar that is regularly used to fill the area under the dome plates. These voids allow for water-ingress to the rock bolt assembly, which results in corrosion of rock bolt components and eventually failure. In addition, the current installation technique consists of several manual steps with intense labor works that are usually done in uncomfortable and exhausting conditions, e.g., under the roof of the tunnels. Such intense tasks also lead to a considerable waste of materials and execution errors. Moreover, adequate quality control of the execution is hardly possible with the current technique. To overcome these issues, a nonshrinking/ expansive cement-based mortar filled in the paper packaging has been developed in this study which properly fills the area under the dome plates without or with the least remaining cavities, ultimately that diminishes the potential of corrosion. This article summarizes the development process and the experimental evaluation of this technique for the installation of rock bolts. In the development process, the cementitious mortar was first developed using specific cement and shrinkage reducing/expansive additives. The mechanical and flow properties of the mortar were then evaluated using compressive strength, density, and slump flow measurement methods. In addition, isothermal calorimetry and shrinkage/expansion measurements were used to elucidate the hydration and durability attributes of the mortar. After obtaining the desired properties in both fresh and hardened conditions, the developed dry mortar was filled in specific permeable paper packaging and then submerged in water bath for specific intervals before the installation. The tests were enhanced progressively by optimizing different parameters such as shape and size of the packaging, characteristics of the paper used, immersion time in water and even some minor characteristics of the mortar. Finally, the developed prototype was tested in a lab-scale rock bolt assembly with various angles to analyze the efficiency of the method in real life scenario. The results showed that the new technique improves the performance of the rock bolts by reducing the material wastage, improving environmental performance, facilitating and accelerating the labor works, and finally enhancing the durability of the whole system. Accordingly, this approach provides an efficient alternative for the traditional way of tunnel bolt installation with considerable advantages for the Swedish tunneling industry.