Backfill Grouting Research Articles

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

In this study, based on unsaturated soil theory, the diffusion behavior of shield tunnel back-fill grouting in unsaturated strata was considered, and Van Genuchten equation was introduced for deriving calculation formula for grouting diffusion radius. Then, an analysis flow for the influence of back-fill grouting parameters on seismic performance of shield tunnel was proposed, and the analysis was carried out with an actual project example. The results show that, compared to the saturated state, owing to the existence of matrix suction in the unsaturated soil, the permeability of the stratum is reduced, resulting in a slower increase in the grouting diffusion radius and smaller ultimate grouting distance. In this project, after using asphalt-cement grouting material, increasing the grouting time and grouting pressure, as well as reducing the elastic modulus of the material can decrease the seismic response of the tunnel. When the grouting time t = 60 min, grouting pressure P0 = 0.5 MPa, elastic modulus E = 49.1 MPa, the seismic-reduction rate of the structure can reach 25.65%. Finally, the fitted equations for the grouting time, pressure, and elastic modulus of the grouting material with the relative displacement and seismic-reduction rate of the tunnel were obtained.

Backfill grouting diffusion law of shield tunnel considering porous media with nonuniform porosity

Current studies usually do not consider the effect of spatially inhomogeneous distribution of formation parameters on grout diffusion caused by shield tail voids. To solve the above problem, this study proposes a nonuniform pore model for porous media formation and establishes a one-dimensional penetration grouting diffusion model considering the spatial nonuniformity of formation pores under the condition of constant grouting pressure. This model was used to analyze the penetration diffusion behavior of grout in the strata and the influence of parameters such as grouting pressure, water-cement ratio, and formation displacement. The numerical solution was provided by the finite element software COMSOL. According to the degree of cement particle blockage, it is pointed out that there is an injectability control zone in the grouting process. A one-dimensional visualized penetration grouting diffusion simulation system considering the shield tail gap was designed, and a grouting diffusion test was carried out with cement slurry. The results show that grouting pressure, water-cement ratio, and soil displacement have a significant influence on the grout deposition process. The higher the grouting pressure, the lower the water-cement ratio, the faster the formation turns into the non-injectable state. The grouting pressure has little influence on the injectable control zone, while the larger the water-cement ratio, the greater the displacement of the formation, and the farther the injectability control zone is from the grouting hole. By comparing the nonuniform pore model with grouting test, the rationality of the nonuniform pore model is verified, which provides guidance and a basis for backfill grouting.

RETRACTED:vertical ground battery borehole heat exchanger filled with the phase change material

This paper investigates the transient thermal performance of a single u-tube vertical ground heat exchanger in which n-octadecane PCM material is considered as a backfill grout material. The analysis is performed based on the Crank-Nicolson finite difference numerical method which is a very stable numerical technique. Transient thermal characteristics of the battery borehole heat exchanger such as temperature variation of the PCM, soil, and the working fluid with respect to time and depth is presented in the analysis. Furthermore change in liquid fraction of the melting PCM with respect to time is expressed with the analysis. Finally it is concluded that the implicit numerical technique is suitable for long simulation time as the simulation is carried out for 3600 h of simulation.

Analytical modeling of complex contact behavior between rock mass and lining structure

Based on the nondestructive test data of operating railway tunnels in China, this paper summarizes the basic characteristics of the complex contact behavior between the rock mass and lining structure. The contact modes are classified into dense contact, local non-contact, and loose contact. Subsequently, the corresponding mechanical model for each contact mode is developed according to its mechanical characteristics using the complex variable method. In the proposed mechanical model, a special algorithm is introduced to detect whether the local non-contact zone is re-contacted. Besides, a novel conformal mapping method is also proposed to accurately calculate the mechanical response of the concrete lining. Finally, the accuracy of the proposed method is verified by comparing it with the finite element method (FEM). Several parameter investigations are conducted to analyze the effects of different contact modes on the rock–lining interaction. The results show that: (i) the height of the local non-contact area does not have a significant effect on the contact stress distribution if no re-contact occurs; (ii) backfill grouting can reduce the local stress concentration caused by poor contact modes; and (iii) reducing the friction coefficient of the interface can lead to a more uniform distribution of internal forces in the concrete lining.

Multiphysics modelling of backfill grouting in sandy soils during TBM tunnelling

Multiphysics modelling of backfill grouting in sandy soils during TBM tunnelling

Bed Separation Characteristics of an LTCC Panel and Subsidence Controlling Grouting: Case Study of Longquan Coal Mine, China

The bed separation backfill grouting (BSBG) is commonly used to mitigate the surface subsidence caused by coal mining. The distribution characteristics of bed separation and its dynamic evolving process are crucial for BSBG design. This paper utilizes the continuum-discontinuum element method (CDEM) to study the distribution characteristics of bed separation for a longwall top coal caving (LTCC) panel of Longquan coal mine. Numerical results indicate that in addition to the bed separation below the primary key stratum, several small bed separations may also occurred in the strata between the primary key stratum and the subordinate key stratum. The bed separations in the overburden could be classified into three classes: the upper bed separation, the middle bed separation, and the lower bed separation. The upper bed separation has the longest duration time, and the middle bed separation has the shortest duration time. And the BSBG should be started before the closure of the middle bed separation. Based on the actual geological information, the BSBG scheme for 4203 LTCC panel is proposed to mitigate the surface subsidence by taken the results of numerical simulation into consideration. In addition, the case study of the BSBG is introduced in detail. By using gangue power slurry, BSBG could not only effectively mitigate the surface subsidence but also solve the problems of environmental pollution and land occupation caused by traditional gangue stacking. The present study could provide technical support for surface subsidence mitigation and coal gangue disposal for LTCC mining with similar conditions.

Selection of backfill grout for shallow geothermal systems: Materials investigation and thermo-physical analysis

A main aspect of the geothermal well design is the selection of grouts backfilling the space between a geothermal probe and the surrounding ground, taking into consideration the mineralogical, thermo–physical, mechanical and flowability properties. The EU GEO4CIVHIC project aimed at developing efficient and cost-effective geothermal systems suitable for the air-conditioning refurbishment of urban buildings. A selection of different grouts was performed to ensure the whole efficiency of shallow geothermal heat exchangers designed within the project. Experimental tests were executed to identify flowable grouts with the best possible combination of different material properties, while also fulfilling a competitive cost target set forth in the preliminary project cost analysis. Grout acceptance criteria were defined: a working time of at least 4 h, a water bleeding target of 2% and a volumetric shrinkage upper bound of 4%, a thermal conductivity in water saturated conditions of at least 1.4 to 1.5 Wm−1K−1, a compressive strength range of 1 to 2.1 MPa, a flow time range of 60 ± 15 s. Two out of six commercial grouts were selected for installations onsite.

Research of asphalt–cement materials used for shield tunnel backfill grouting and effect on anti-seismic performance of tunnels

Backfill grouting is a key technology in shield tunnelling, and in this study, the process of backfill grouting in stable strata and soft soil strata was analyzed. Through a series of laboratory tests, asphalt–cement (A-C) materials suitable for backfill grouting of shield tunnels were investigated. Regression fitting equations were established between the proportioning of raw materials and the grouting performance indexes of A-C materials by multiple regression analysis. Then, based on a practical engineering, the adaptability of A-C materials under different formation conditions was studied from the perspective of anti-seismic performance, and a comparative analysis with conventional backfill grouting materials was conducted. The results show that the relative displacement peaks of the tunnel lining under seismic action did not change significantly after backfill grouting with different materials. Backfill grouting with A-C materials can reduce the maximum principal stress peaks of the tunnel lining by up to 54%, and A-C grouting materials are recommended for backfill grouting in the stable stratum section. The use of this material can improve the anti-seismic performance of shield tunnels compared to conventional backfill grouting materials.

Preparation and engineering properties of alkali-activated filling grouts for shield tunnel

Alkali-activated materials (AAM) have attracted extension attention as a promising alternative to ordinary Portland cement (OPC) in many applications. Back-fill grouting is a key procedure in shield tunnel construction. In view of the deficiency of traditional OPC-based grout in consuming natural resources and polluting the environment, it is of great significance to develop low carbon and environmentally friendly alkali-activated grouts (AAG). In this study, AAG used for back-fill grouting in shield tunnels were prepared with fly ash, ground granulated blast-furnace slag and steel slag as the main cementitious materials, supplemented by fine sand and additive. Through laboratory tests, the effects of factors including the concentration of the alkaline activator solution and liquid-to-solid ratio on the performance of AAG were studied systematically. Moreover, the performance of AAG was analyzed and evaluated in terms of basic physical properties, working properties, hardening properties and pore structure properties, and two representative groups of AAG (AAG-Ⅰ and AAG-Ⅱ) were recommended by comparing with a typical OPC-based grout. The results show that the setting time, fluidity and its loss rate over time of AAG can be adjusted in a wide range, and AAG can be flexibly selected for use according to the requirements of grout performance for specific construction cases. By adjusting the ratio parameters of AAG, the 28-day underwater/in-air strength ratio and impermeability pressure of AAG can reach over 0.80 and 0.8 MPa, respectively, showing excellent water dispersion resistance and impermeable performance, while AAG have excellent working properties. Compared with the typical OPC-based grout, AAG-Ⅰ shows better engineering performance.

Selection of backfill grouting materials and ratios for shield tunnel considering stratum suitability

In shield tunnel engineering, there is no uniform standard for the selection of backfill grouting materials and ratios. In this study, to facilitate the selection of a grout, the applications of grout types, materials, and ratios were summarized based on a statistical analysis of engineering cases. Through laboratory tests and range analysis, the relationships among the basic grout performance and ratios were examined. The reference values of the grout ratios and performance requirements in different strata were obtained using statistical methods and by regression analysis. The results showed that the grout type used in engineering is mainly a single-component grout; in strata with groundwater, the usage rate of modified grouts is significantly high. The single-component grout ratio for clay is the most affected by groundwater; for all strata, the change in the B/S ratio is the most significant. The W/B ratio is the most important factor affecting the basic grout performance, and the demand for compressive strength varies the most in all strata.

Study of the shear strength evolution over time of two-component backfilling grout in shield tunnelling

The two-component backfilling system is the most commonly used method to fill the annular void created during the advancement of shield machines. This unavoidable void, strictly linked to the technology of shield machines, must be filled continuously in order to avoid mostly surface displacements and lining movements. Today, this technology is the most frequently used due to operative and technical advantages, which lead to economic savings. However, despite intensive use of this backfilling technology, very little information is currently available concerning the evolution of the material in function of the curing time. Historically, the uniaxial compressive strength has been used as the main parameter for testing the compliance of a certain grout with the site-specific technical requirements, but nowadays shear strength is also starting to be considered by designers even if this topic has never been investigated.In this work, a laboratory test campaign focused on shear strength and its evolution in function of curing was performed. These tests put alight the fast mechanical growing of the two-component grout from the shear strength point of view and it should be remarked that at the current state of research there are no investigations concerning the shear strength in the context of a drainage approach.Both short and long curing times were investigated according to the direct shear test, performed under drained conditions. The Mohr-Coulomb failure envelope model was selected for the study and its widening in time highlights the peculiarity of this technology. Starting from a liquid phase at t0, values of cohesion (c’) and friction angle (φ’) grow in function of curing, reaching 126 kPa and 22° at 3 h and exceeding 270 kPa and 40° at 28 days.

Earth Pressure and Internal Forces of Tunnel Lining in Jet Grouting Reinforced Mud Stratum

In this study, field measurements of the earth pressures and the main reinforcement strains were carried out at three shield tunnel linings in mud stratum reinforced by vertical jet-grouted piles during tunnel construction and post-construction. The measured strains were used to back-calculate the linings’ internal forces. The measured earth pressures and the back-calculated internal forces were compared to corresponding design values. The results indicate that the earth pressure and the internal forces increased rapidly, before exhibiting a fluctuating decrease and finally a long-term slow change, after lining assembly. The vertical jet-grouted piles were beneficial to mobilise the soil arching effect and led to the real earth pressure on the lining significantly smaller than the full overburden pressure, even with a relatively shallow buried depth. The vertical jet-grouted piles intensified the influence of backfill grouting on the earth pressure and caused the lining segments near the backfill grouting holes to continuously bear more radial pressure in the long-term. The resultant internal forces during lining assembly were large, and the Conventional Model failed to consider this element of the internal forces. The findings can provide a reference for the design and the construction of similar projects.

Simplified Analytical Method for Predicting the Lateral Ground Displacements due to Shield Tunnelling

Earth pressure balance or slurry shield tunnelling will squeeze the subsoils and lead to lateral outward ground displacement. However, current methods to estimate the shield tunnelling-induced ground displacements generally use the methods based on the face unsupported tunnelling (e.g., New Austrian tunnelling and open shield excavation), which cannot predict the lateral ground movement due to shield tunnelling. In this paper, a novel simplified analytical method is proposed to predict the ground lateral displacement during the shield advancing process. The key shield tunnelling operation factors, including the additional pressure of cutter head, the friction forces around shield body, the back-fill grouting pressure, and the soil volume loss are all considered. The lateral ground displacements induced by the four former factors are calculated by using Mindlin’s solutions. The soil volume loss-induced lateral ground displacement is calculated by employing the expression introduced by Pinto and Whittle. Combining with the displacement obtained from all the factors, the analytical method for lateral ground displacement induced by shield tunnelling is obtained. The applicability of the proposed analytical approach is verified with three well-documented case histories involving slurry shield and EPB shield machines.

Non-linear spring model for backfill grout-consolidation behind shield tunnel lining

This study presents a non-linear spring model for modelling the backfill grout consolidation behind shield tunnel lining. Two important parameters, i.e. the time-dependent grout pressure decay induced by consolidation and the grout-cake thickness, were derived through a non-linear spring model and continuity equation. The proposed non-linear spring model for backfill grout consolidation was validated based on vertical pressure and strain relationships determined from an oedometer test. The derived equations were applied to the Groene Hart Tunnel (GHT) project. The results show that the calculated grout pressures agree well with the measured values. The calculated grout-cake thicknesses are in good agreement with the measured values. Two key factors influencing the grout consolidation are discussed: grout diffusion into the soil, and the initial distribution of the grout injection pressure. It is found that grout diffusion into the soil can dissipate the grout pressure quicker than grout consolidation. The distribution of the initial grout injection pressure dominates the final distributions of the grout pressure/grout cake around the tunnel lining.

Model study on backfill grouting in shield tunnels based on fractal theory

Fractal theory demonstrates significant merit in the feature expression of forms of matter in nature. This study uses fractal theory to study the backfill grouting of a shield tunnel. The seepage path was considered as a seepage mesh inserted into the rock-soil mass. For the fractal features of the seepage mesh, the formulas for the diffusion distance and the pressure contribution of grout were derived. The results showed that the diffusion equations of different grout patterns (Newtonian fluid and Bingham fluid) were of a uniform form after calculation, and the equations for the pressure distribution of grout with a change in radius were identical. The diffusion distance of grout increased with increasing grouting time, and there was no indication that the development of diffusion distance tended to be gradual; the downward tendency of the grout diffusion velocity was not moderated. The segment pressure increased with an increase in the diffusion distance. With a constant diffusion distance, a greater grouting pressure produced a greater segment pressure. The favorable performance of grout was attributed to an appropriate mixture ratio. An improper mixture ratio resulted in a smaller reinforcement area in the stratum, which impaired the stability of the shield tunnel.

Review of Shield Tunnel Backfill Grouting Tests and Its Diffusion Mechanism

Review of Shield Tunnel Backfill Grouting Tests and Its Diffusion Mechanism

A diffusion model for backfill grout behind shield tunnel lining

AbstractThis paper presents an analytical model to investigate backfill grout diffusion behind tunnel segmental lining, in which the backfill grout is taken as a Bingham fluid. The analytical model of grout diffusion is derived based on force–equilibrium principle, Darcy's law, and the law of momentum conservation of the grout. Time‐dependent grout diffusion pressure and distance are highlighted in the model. The proposed grout diffusion model is applied in two field cases: Metro Lines No. 9 and No. 4 in Shanghai City. The results show that the proposed model agrees well with the measured grout diffusion distance in the field. Parametric studies are then conducted, implying that grout diffusion distance along the radial direction of tunnel lining is proportional to either hydraulic conductivity or initial grout pressure, whereas it is in inverse proportion to the yield stress of backfill grout. The distributions of initial grout pressure exert key influences on the grout diffusion distance and grout diffusion pressure behind tunnel segment lining.

The life-cycle development and cause analysis of large diameter shield tunnel convergence in soft soil area

The tunnel convergence is an important index of the construction quality and operation safety. In the past, most of researches were focused on the shield tunnel lateral convergence and its effect on the safety at operation period. In this paper, by employing the 3D laser scanning test method and convergence ellipse fitting identification technology, the shield tunnel full space convergence can be tested and divided into three typical modes: transverse ellipse, oblique ellipse and vertical ellipse. Based on series of field tests in three large-diameter tunnels under construction and operation, the spatial distribution and life-cycle development laws of above three typical convergence modes were firstly seriously studied, the changes of the long axis, short axis and deflection angle of above convergence modes are given. Meanwhile, the generation mechanism and main cause is studied by analysis of machine-structure interaction, soil pressure and back-fill grouting action during shield construction. It is found, in the soft soil areas, the formation of different convergence modes mainly depends on the initial load condition at the stage of segments leaving the shield tail, and the following action of back-fill grouting will have little effect on the structure convergence, but most on the surrounding soil deformation. Subsequently, the convergence will continue growth with the short axis deformation greater than the long axis, and gradually develop towards symmetry with soil consolidation. Besides that, the obvious coupling relationship between the convergence and the longitudinal settlement can also be found after long-term operation from the tests. The above findings are very helpful to fully understanding the stress and deformation interaction during the large diameter shield tunnel construction and operation.

Lattice Boltzmann simulation for grout filling process during simultaneous backfill grouting of shield in tunnel construction

Over the years, it has become obvious that simultaneous backfill grouting is of great significance to the design of the tunnel lining and process control of shield construction. It is essential to know the grout pressure distribution around the tunnel lining. The purpose of this study is to seek an alternative method to simulate the grout diffusion process and obtain pressure distribution of different time during simultaneous backfill grouting of tunnel construction. A lattice Boltzmann method (LBM) based free surface flow model is introduced and modified, and a Smagorinsky large-eddy simulation model serves to deal with the small-scale turbulent problem, which is a challenge for LBM to simulate the large-scale real-world engineering. The simulation results obtain the grout filling state with time and pressure distribution around the tunnel lining. Additionally, the grout pressures on site are measured at a ring in line 8 of Chengdu Rail tunnel, and the measurement results are also compared with ones taken from numerical simulation, it is showed that the numerical results are consistent with that of measurement on the whole. Through simulating different grouting strategies, it is concluded that for four-holes grouting schemes, the grouting pressures of upper holes are significant for the grout pressure distribution and should be paid most attention in construction.

Influence of Loose Contact between Tunnel Lining and Surrounding Rock on the Safety of the Tunnel Structure

The improvement of the contact state between the surrounding rock and tunnel lining, such as the effect of back-fill grouting behind lining, was important for maintaining the stability of the lining structure. To explore the influence of loose contact states behind lining on the safety of tunnel lining, a case of field investigation in a railway tunnel with a symmetrical lining structure was presented in this paper. A model test was conducted to prove the accuracy of the numerical simulation in the condition of dense contact state between the lining and surrounding rocks. Based on this, the three-dimensional (3-D) impact of loose contact states on the mechanic behavior of the lining structure under different compactness and different loose contact areas behind lining was investigated and summarized. Furthermore, the influence of the percentage of the insufficient strength behind lining was explored. Finally, the grade of the influence of the loose contact state on the safety of the lining structure was classified. The results revealed that: (1) in order to maintain the stability of lining structure, the compactness of the back-fill grouting behind lining was recommended to be above 80%, and the range of the loose contact area should be no more than 60 degree; (2) the strength of the back-fill grouting behind lining should be above 50% strength of the surrounding rock, the loose contact state behind lining should be improved in time to avoid expansion of the loose contact area; and (3) the classification of the influence grade on the safety of the lining structure provides a basic reference for controlling the quality of the back-fill grouting. This research gives a new point of view for the evaluation of the contact state between lining and surrounding rock.