Optimization of Slab Bottom Grouting: A Case Study Utilizing an Underplate Grouting Model with Brinkman Equation and Level Set Method

In order to fully mechanized caving face bypass collapse column on safety and high efficiency, this paper do similarity simulation experiment, and obtained experimental result that main type of seepage flow includes finger seepage and surface seepage, the grout enter into around pore and occupy it’s space in grouting pressure. Moisture content of mud and sand medium is lower, grouting process can be regarded as single-phase permeability, analysis on the relation between grouting diffusion radius and other parameters. may know that grouting diffusion radius is increased with the increase of permeability coefficient and grouting pressure and grouting time, and is decreased with the increase of Porosity and grout viscosity.

ABSTRACTToday, grouting is used as an aid in ground improvement in most civil and mining engineering projects. Groutability and grout penetration depth are among the most important issues that are considered in grouting operation. Various parameters such as in-situ stress, pore water pressure, joint geometric and geomechanical characteristics, grout properties (viscosity and yield stress) and technical factors such as grouting pressure and flow rate affect the groutability and grout penetration depth in a jointed rock mass. Knowledge of the effect of these parameters has advantages in the prediction of grouting results. Typically, cement-based grout is used in jointed rock masses. Unlike water, stable cement-based grout usually acts as a Bingham fluid. In this study the effect of important parameters on grouting process in a jointed rock mass was investigated numerically using the DEM method. In the conducted study, the problem geometry represents a horizontal section in a regularly jointed rock mass with two joint sets. The analyses results show that the grout penetration depth and intake increase as joint aperture, normal stiffness and grouting pressure increase and in-situ stress and pore water pressure decrease. Increase in joint spacing does not have any effect on the grout penetration depth but decreases the grout intake. The effect of joint orientation on grouting process is strongly dependent on in-situ stress state. On the other hand, increase in grout yield stress decreases the grout penetration depth and intake, while grout viscosity does not have any effect on maximum grout penetration depth and intake. To further investigate the above mechanisms, the grouting process conducted in Gotvand dam-Iran was simulated numerically.

The influence of the grout properties on the grout pressure distribution around a tunnel lining is investigated. Initial yield stress of the grout and consolidation properties appear of importance. The consolidation properties are determined by means of element tests and appeared also to be influenced by the properties of the soil surrounding the tunnel. Field measurements have shown that grout pressures vary during the bore-cycle. This is attributed to consolidation of the grout. The vertical pressure gradient over the lining decreases with increasing distance from the TBM. It is shown that at some distance from the TBM the grout pressure is in most cases comparable to the pore pressure for a tunnel drilled in sand. The grout applied influences the vertical loading on the lining. For this loading it is of importance that the unsupported part of the lining (where buoyancy forces dominate) is as short as possible to reduce the momentum in the lining and high vertical forces at the TBM and there where the grout is hardened. This can be achieved in three different ways: The grout has a relatively high initial shear stress. In a situation with a high initial shear stress of the applied grout, the shear strength in the not yet hardened grout is already sufficient to prevent upward movement of the tunnel lining. Subsoil and grout allow for a rapid consolidation of the grout, resulting in an increase of allowable shear stress in the grout and as a result in only a limited unsupported length of the lining. The grout used hardens quickly. This also leads to a limited unsupported length of the lining. These three methods can be used for a tunnel made in sand. For a tunnel in clay the second option is not possible, because the low permeability of the clay prevents consolidation of the grout. Results of field measurements on grout pressure decay during standstill of the TBM have been analysed in combination with the results of element tests. Grouts normally consolidate after injection into the tail void. This leads to a reduction of grout volume and to a decrease in grain stress. It was found for several tunnel projects, where a tunnel was bored in sand, that the final pressure distribution around a tunnel was comparable to the pore water pressure and was more or less independent from the injection strategy. Only the initial pressure distribution directly behind the TBM can be influenced by the injection strategy. Grout properties in combination with the soil properties influence the loading on the lining directly behind the TBM. It is therefore necessary to select a grout taking in into consideration the soil properties at the location and desired grout properties (yield stress, bleeding and hardening parameters). (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Numerical and analytical analyses of the effects of different joint and grout properties on the rock mass groutability

The grout pressure in the shield tunnel tail void during synchronous grouting is the key to controlling ground settlement and restraining the segment. However, the circumferential, longitudinal, and radial distribution of grout pressure considering the temporal variation in grout viscosity has not been well explored yet. In this study, a theoretical model of grout pressure distribution and dissipation considering the temporal variation in Bingham grout viscosity was established. The simulation results of the pressure model were verified by field-measured data. The results showed that the radial and longitudinal distributions of grout pressure considering the temporal variation in grout viscosity were closer to the field-measured data. The impacts of the main parameters on the pressure distribution and dissipation were analyzed. Compared with the effect of the shield tail void thickness, tunnel radius and yield shear stress have greater effects on grout pressure during the circumferential filling phase. During the longitudinal and radial diffusion phases, the increase in soil porosity and permeability coefficient was conducive to grout diffusion. The increase in the grout viscosity reduces the pressure loss during the grout flow process. The results of this research can provide a theoretical basis for the grout design process in shield tunnels.

Study on the Influence of Back-fill Grouting Parameters in Unsaturated Strata on the Seismic Performance of Shield Tunnels

Clarifying the mechanism of grouting to block karst water outbursts is essential for ensuring effective sealing. This article studies the grouting blocking problem related to the prevention and control of water surge disasters in karst tunnels, focusing on the grouting blocking mechanism of efficiently plugs expanding material (EPEM) under dynamic water conditions. We propose a grouting diffusion formula and blocking criterion that take into account the self-expanding properties of the slurry. First, based on the equilibrium relationship between the friction force and anti-splitting force between the blocking body and the rock wall, we establish an effective blocking condition. Second, by combining capillary theory with Newton’s fluid constitutive equation, we derive the diffusion distance formula for self-expanding slurry under dynamic water conditions. We then construct a mechanical model that uses the length of the critical blocking body as a criterion, revealing the coupling influences of groundwater pressure, grouting pressure, and grouting time. The results indicate that groundwater pressure is positively correlated with grouting pressure and grouting time, while grouting pressure is negatively correlated with grouting time. Finally, we verify the practicality of the proposed criterion through the project at Quanmutang Reservoir in Hunan Province, successfully implementing a parameter combination of 0.5 MPa grouting pressure and 20 min of grouting time to block surge water. This research provides a theoretical basis and engineering guidance for designing water surge grouting in karst tunnels.

The influencing factors of grouting diffusion in broken rock mass were divided into four classifications: grouting pressure, grouting time, permeability coefficient and grout viscosity. Relations among similar factors were expressed to each other using an equation. Empirical formulas of relations among grout water-cement ratio, viscosity and time between the joint density of broken rock mass and permeability coefficient, and between water absorption and permeability coefficient were established. The differences among the four diffusion radius formulas grouting in porous continuous media were compared. A new empirical formula of diffusion radius was obtained using multivariate nonlinear fitting analysis based on the mean value of the four empirical formulas. The tests of grouting diffusion in broken rock mass were done in the field. The mean empirical formula is consistent with the measured value of the field tests on grouting diffusion radius, which provide a reference for the design of grouting into broken rock mass.

To investigate the anchoring performance of self-drilling anchors in gravel-cobble strata, this study conducted indoor orthogonal tests based on soil grouting experiments to simulate actual construction conditions. The influence of fine particle content, grouting pressure, and water-cement ratio on anchoring parameters was analyzed. Additionally, a grouting simulation model was developed using PFC2D 5.0 numerical software to examine the effects of grouting pressure, drilling speed, and grout viscosity on the grout diffusion radius through orthogonal and single-factor experimental schemes. The results demonstrate that: fine particle content exerts the most significant impact on anchoring performance, with higher content reducing peak pullout resistance; the grout diffusion radius exhibits a positive correlation with grouting pressure but a negative correlation with drilling speed and grout viscosity, with viscosity having the strongest influence, followed by pressure and speed; the diffusion pattern follows a gradually decreasing trend along the drilling direction, while the radius increases at a diminishing rate with elevated pressure; when viscosity ranges from 83.3 to 833.3 mPa·s, the diffusion radius decreases by 72%; and multivariate regression analysis indicates a power function relationship between the diffusion radius and these three parameters.

The “expansion–injection” anchoring technology of anchor cables in the bottom plate of soft rock roadways can not only give full play to the advantages of expansion anchoring to improve the anchoring effect of anchor cables in soft rock roadways, but also enhance the bearing capacity of the injected rock mass through grouting, thereby optimizing the stress distribution of the bottom plate and reducing the damage of the surrounding rock caused by tensile stress. Since the selection of grouting process parameters will directly affect the diffusion range and penetration effect of the grout, and the selection of grouting process parameters is often determined by experience and lacks scientific basis, this study uses numerical simulation to explore the influence of common grouting parameters such as grouting pressure, grouting time and the spacing of grouting anchor cables on the diffusion range of the grout. In order to provide a scientific basis for optimizing the design of roadway support. The numerical analysis results show that the grout diffusion radius increases nonlinearly with the increase of grouting pressure, while the expansion efficiency of the grout diffusion range gradually decreases and tends to be stable with the increase of grouting time. Meanwhile, a larger spacing of grouting anchor cables is not conducive to the formation of the grouting reinforcement area of the base plate. Finally, the reasonable parameter range was determined as the grouting pressure of 3-4 MPa, the grouting time of 8-10 minutes, and the anchor cable spacing of 2.5-3 m.

Because of the limitation of mining techniques and economic conditions, large amounts of residual coal resources have been left in underground coal mines around the world. Currently, with mining technology gradually developing, residual coal can possibly be remined. However, when residual coal is remined, caving areas might form, which can seriously affect the safety of coal mining. Hence, grouting technology is put forward as one of the most effective technologies to solve this problem. To study the grouting diffusion in fractured rock mass, this paper developed a visualization platform of grouting diffusion and a three-dimensional grouting experimental system that can monitor the grout diffusion range, diffusion time and grout pressure; then, a grouting experiment is conducted based on this system. After that, the pattern of the grouting pressure variation, grout flow and grout diffusion surface are analyzed. The relationship among some factors, such as the grouting diffusion radius, compressive strength of the grouted gravel, porosity, water-cement ratio, grouting pressure, grouting time, permeability coefficient and level of grout, is quantitatively analyzed by using MATLAB. The study results show that the flow pattern of the grout in fractured porous rock mass has a parabolic shape from the grouting hole to the bottom. The lower the level is, the larger the diffusion range of the grout is. The grouting pressure has the greatest influence on the grouting diffusion radius, followed by the grouting horizon and water-cement ratio. The grouting permeability coefficient has the least influence on the grouting diffusion radius. The grout water-cement ratio has the greatest influence on the strength of the grouted gravel, followed by the grouting permeability. The grouting pressure coefficient has the least amount of influence on the grouting diffusion radius. According to the results, the grouting parameters are designed, and a layered progressive grouting method is proposed. Finally, borehole observation and a core mechanical property test are conducted to verify the application effect. This grouting technology can contribute to the redevelopment and efficient utilization of wasted underground coal resources.

6579 Background: Collecting electronic patient reported outcomes (ePROs) reduces the burden of cancer and prevents acute care hospitalizations. However, broad implementation in the routine care setting remains challenging, partly because the optimal implementation strategies – actions that are most likely to encourage adoption and use – are not known. Since 2019, the SIMPRO Consortium has deployed an ePRO-based symptom management program (eSyM) across 6 community-based cancer centers. Methods: We used statistical process control (SPC) charts to identify variation due to special versus common causes (random variation) for one key performance indicator (KPI) – the weekly ePROs response rate. All 6 SIMPRO sites contributed data for this analysis: 3 for chemotherapy patients and 3 for surgery patients. Sites had to have at least 18 months of KPI data; information from the first 4 months after eSyM rollout were excluded to account for program ramp-up. The KPI was calculated as the number of patients who submitted an ePRO questionnaire divided by the number eligible to submit a questionnaire each week. The upper and lower confidence limits were set at +/- 2 sigma to allow for 95% of observations to fall within the limits. Three rules were applied to identify special cause variation: 1) astronomical points (outside sigma limits), 2) shifts (8 or more points above or below a center line), and 3) trends (6 or more points consecutively ascending or descending). Implementation strategies that mapped to special cause variations were selected as those most likely to impact the KPI. Results: Across the 6 sites that deployed eSyM, the mean KPI performance ranged from 19.7%-35.7%. SPC charts detected multiple special cause variations in the KPI at all 6 sites, though the patterns varied by site. All sites demonstrated positive and negative astronomical variations as well as positive and negative shifts. Three sites demonstrated negative trends; no sites demonstrated positive trends. Direct patient outreach was the implementation strategy most frequently associated with special cause variation, followed by changes in promoting the ePRO program to clinical staff. Positive changes were associated with strategy initiation; negative changes were associated with strategy discontinuation. Conclusions: Applying SPC charts to a KPI from the eSyM deployment highlighted the effect of personal communication with patients and providers, suggesting that these implementation strategies could offer value to other sites deploying eSyM. The absence of positive trends early in eSyM program deployment underscores the need to identify better implementation strategies and allocate more resources to foster program adoption and sustainability. Applying SPCs to other KPIs, such as symptom severity and healthcare utilization, could improve eSyM deployment and impact.

Rheological characteristics of cement-sodium silicate grout in its fluid–solid phase transition process

Cement grouting is an operation often carried out to consolidate and seal the rock mass in dam sites and tunnels. The quality and efficiency of a grouting operation depends on various factors such as water take, grout properties and grouting pressure. One of the parameters which have the highest effect is pressure since the application of excessive pressure causes the hydraulic fracture phenomenon to occur in the rock mass and too little pressure leads to incomplete grouting and failure to seal the site in a perfect manner. Mathematical modeling is used for the first time in this study to predict and determine the optimum pressure. Thus, the joints that exist in the rock mass are simulated using cylindrical shell model. The joint surroundings are also modeled through Pasternak environment. To obtain equations governing the joints and the surroundings, energy method is used accompanied by Hamilton principle. In the end, an analytical solution method is used to obtain the maximum grouting pressure. In order to validate the modeling, the grouting pressure values obtained by the model were used in the sites of Seymareh and Aghbolagh dams and the relative error rates were measured considering the differences between calculated and actual pressures. Modeling in the examined sections of Seymareh dam showed 29.61, 5.57, 21.98, 32.50 and 9.09 percent error rates and in the sections of Aghbolagh dam it rendered the values of 4.32, 5.40 and 2.96 percent. The results indicate that this modeling can be used to estimate the amount of pressure for hydraulic fracture in grouting, to predict it and to prevent it.

Evaluation of the Traffic Speed Deflectometer Data Using Simplified Deflection Model