Grout Layer Research Articles

Interface debonding detection of grouted connection based on Lamb wave energy leakage

Grouted connections (GCs) are transitional elements that have been extensively employed in offshore wind turbine support structure to transfer loads from superstructure to foundation. However, interface debonding defects between steel tube and grout layer have an adverse effect on the durability and fatigue resistance of the GC. An effective interface debonding defects detection approach for GC is necessary. In this study, interface debonding defects detection approach based on Lamb wave energy leakage was proposed and validated numerically and experimentally. Numerical studies on Lamb wave energy leakage models and the GC models were performed to study mechanism of detection approach. Lamb wave is excited on the surface, and stress wave fields and time-history response of models were extracted and compared. Experimental investigations were carried out to verify the applicability of the proposed approach in practice. A scaled GC specimen was constructed and Lamb wave was excited by the PZT patches mounted on the surface of GC specimen. The output voltage of surface-mounted PZT sensors under different axial loads were compared. Both numerical and experimental results show that the proposed approach is effective to the detection of interface debonding defects. The damage evolution index (DEI) based on wavelet packet energy is defined and it can be adopted to qualitatively determine the initiation and evolution of the damage.

A fully coupled hydraulic-mechanical model of deep tunnel considering permeability variation

When the buried depth of underground engineering exceeds 1000 m, the deep surrounding rock will show typical nonlinear deformation characteristics due to the coupling effect of high in-situ stress, and high seepage pressure. The stress field of surrounding rock will change the distribution characteristics of seepage field, and in turn, the change of seepage field will affect the distribution of surrounding rock stress field, which is a process of mutual influence and interaction. Considering the variation of permeability coefficient of deep surrounding rock and non-Darcy flow movement of fluid, a fully coupled hydraulic-mechanical analytical model of deep tunnel was proposed based on Hoek-Brown criterion and effective stress principle, and the detailed application method of the model was also given. Through the triaxial compression test under hydro-mechanical coupling, the nonlinear softening model considering seepage pressure and permeability variation equation were established, which solved two key problems of the model. The corresponding numerical calculation program was compiled based on ABAQUS finite element platform, and the reliability of the calculation program was verified by comparing with the model test results. The influence of the thickness of the grouting layer, the permeability coefficient of the grouting layer, the number of drainage holes and the depth of drainage holes on tunnel surrounding rock seepage pressure and lining seepage pressure were calculated and analyzed, and the anti-seepage optimization design of Xianglushan tunnel was carried out.

A solution of radial subgrade modulus by displacement fitting method considering the grout layer for shield tunnels

Subgrade modulus is a critical parameter when analyzing the segmental lining of shield tunnels. However, prevailing analytical solutions of radial subgrade modulus (kr) are based on predefined ideal deformation modes, either circular or oval, which are not consistent with the actual ground deformation, and the influence of the grout layer is commonly neglected. In view of this, this study presents a solution of kr considering the actual deformation of the ground and the grout layer between linings and surrounding ground. A displacement fitting method is proposed to relate kr to the arbitrary distribution shape of ground deformation. With this method, kr for actual deformation consists of a series of radial subgrade moduli (krm) for single deformation modes described by sine and cosine functions. Theoretical solutions of krm considering the influence of the grout layer for single deformation modes are then derived based on the composed ground which is made up of the ground and the grout layer. The influence of the grout layer on krm is then discussed by a parameter study. Moreover, the applicability of the proposed method is illustrated through a design case, where the calculated internal forces agree well with the data from field measurement. The influence of actual ground deformation and grout layer on kr, internal forces, and displacement of shield tunnel is then discussed. Results show that an accurate prediction of kr requires the consideration of the actual deformation of the lining and the influence of the grout layer.

Influence of internal defects of semi grouted sleeve connections on the seismic performance of precast monolithic concrete columns

To investigate the influence of internal defects of semi-grouted sleeve connections on the seismic performance of precast monolithic columns, four specimens of precast monolithic concrete columns with semi-grouted sleeves connecting reinforcement bars were fabricated, including one specimen (PC-D0) with no internal defect and three specimens (PC-D10, PC-D20, PC-D30) with 10%, 20%, 30% of internal defects respectively by controlling the length of anchor bars inside the semi grouting sleeve. The behavior of the columns as well as the failure modes, hysteresis loops, skeleton curves, degradation of rigidity, ductility and energy dissipation capacity were studied based on the data obtained by a low cycle reciprocating test. The results indicate that (1) the precast columns are all damaged by bending and the grouting layer of the assembled columns can be pulled apart easily; (2) the seismic energy dissipation capacity of the column without defects is higher than that of the columns with defects; (3) the existence of internal defects reduces the horizontal bearing capacity, rigidity, ductility and energy dissipation capacity of the assembled columns. However, the peak load for PC-D10, PC-D20 and PC-D30 reaches values respectively equal to 94%, 90% and 84% of that exhibited by PC-D0; (4) the energy dissipation capacity of the defective column with 30% of internal defects is significantly lower than those reached by other columns with defects, a feature that indicates that the influence of internal defects on the energy dissipation capacity of assembled columns is not linear. In conclusion, the results provide an insight into the influence of internal defects of semi grouted sleeve connections on the seismic performance of precast monolithic columns.

Research on Seepage of Jointed Rock Mass of Tunnel and Limited Discharge of Grouting

In underground engineering such as tunnel engineering, the condition of surrounding rock such as water-containing jointed rock mass is a common engineering geology. For broken, water-containing surrounding rock, the reasonable measures to prevent and drain water has always been a key issue. Based on the statistical information of the structural surface of the surrounding rock of the Hongtuzhang tunnel, DIPS software was used to classify the structural plane of the tunnel. Based on the statistical analysis of the occurrence, size, and density of the structural plane, the two-dimensional structural plane network model of the rock mass was established, and the permeability tensor (K1 = 1.61 × 10−6 m/s, K2 = 5.78 × 10−7 m/s) was calculated. Consider the worst orientation, the permeability tensor (K1 = 1.61 × 10−6 m/s) was selected to calculate the grouting design. Based on the theory of limited discharge, the influence of parameters of permeability coefficient ratio n and thickness of grouting layer Tg on the tunnel water inflow and lining external water pressure was analyzed. The recommended value of tunnel drainage was 3.0 m3/m∙d, then the corresponding grouting circle parameters were put forward (permeability coefficient ratio n = 100, thickness of grouting layer Tg = 8 m).

Experimental study of the shear behaviour of concrete-grout-concrete joints

Grouted sleeve connections are currently widely adopted in precast concrete structures. For this kind of connection, there exists a kind of multilayer concrete-grout-concrete joint whose the mechanical behaviour is quite different from that of the new and old concrete interface. Simply following the current bonding theories and conclusions of new and old concrete interfaces will cause uncertainties in the structural analysis and design. In this study, monotonic and cyclic loading tests were both employed to examine the influence of the grouting thickness and the interfacial shear reinforcement ratio on the shear behaviour of this new type of joint. The shear behaviour was also compared with that of the new and old concrete interface. The results showed that the shear capacity of the concrete-grout-concrete joint was lower than that of the new and old concrete interface. Specimens with a thinner grouting layer or with a larger ratio of shear reinforcement have a higher shear capacity. According to the experimental results, the shear transfer mechanism of the concrete-grout-concrete joint was proposed based on the extended friction shear model, and the modified shear capacity calculation model was then established. • Monotonic and cyclic loading tests were both employed to examine the shear capacity of concrete-grout-concrete joint. • The shear capacity of the concrete-grout-concrete joint was lower than that of the old and new concrete interface. • Shear transfer mechanism of the concrete-grout-concrete joint was proposed.

The effect of contact grouting on support load

Introduction. The paper analyzes contemporary methods of frame support design in permanent workings and reveals that contact grouting has received little attention. Contact grouting makes the tight contact between the hardened cement grout and the surrounding rock possible, whereas it is impossible when applying concrete lagging. The paper employs analytical method of arch support, grouting layer, and the surrounding rock calculation considering their softening. Analytical formulae determining support load has been obtained. The formulae take into account strain and strength characteristics of the surrounding rock, hardened cement grout, and support. Support load was calculated under various values of the grouting layer thickness and linear strain modulus and the depth of mining. The dependencies between the support load and the indicated parameters have been obtained, which makes it possible to select the cement grout composition for various mining and geological conditions. Research objective is to determine the effect produced by grouting layer thickness and strain characteristics on arch support load value in order to check its strength in various mining and geological conditions. Methods of research are built upon the physically based analytical methods of geomechanics to solve the problem of interaction between the support, grouting layer, and surrounding rock mass. Results. The results of arched support load calculation are presented for various values of grouting layer thickness, its strain characteristics, and depth of mining. Conclusions. The presence of the grouting layer in the void behind the support has a significant effect on the methods of arch support design. The developed methods take account of the fact that a layer of soft rock develops in the rock mass between the grouting layer and undisturbed rock. When the rock is being broken, its volume in this layer increases, which, in its turn, results in support load transfer growth through the grouting layer. It has been determined that the increase in the hardened cement grout strain and grouting layer thickness reduces support load.

Effectiveness of concrete grouting method for deep-sea pipeline repairs

This study aims to assess the effect of a concrete grouted layer on the collapse pressure of pipes under external pressure. The system consists of a concrete grouting layer and a high-strength plastic jacket. Six specimens with varying degrees of defects are tested to obtain their collapse pressures under external pressure, and four specimens are then repaired. The results show that the repair method restores the collapse pressure of the pipe to 39.15%–100% that of the undamaged pipeline. In addition, a numerical model is established and validated, and systematic parametric studies are conducted to supplement the test results. The experimental and numerical results show that the ultimate collapse pressure of the pipe is significantly influenced by the repair measures of the concrete grouted layer. Based on the parametric study, the main parameters that affect the collapse pressure of the repaired pipes are identified. The relationship between the collapse pressure and the geometry of the concrete grouted layer is analysed, and optimal parameters for the concrete grouted layer are obtained. The results show that installing concrete reinforcement is an effective technology for the rapid repair of defective pipes.

Experimental and numerical investigation of steel-grout-steel sandwich shells for wind turbine towers

Aiming at enhancing a wind turbine tower's performance while keeping its external diameter below transportability-imposed limits, a steel-grout-steel sandwich base segment comprising a high diameter-to-thickness ratio is investigated herein, as an alternative to plain steel towers. An experimental campaign was firstly carried out, involving downscaled tower specimens which comprise the above said cross-section under bending loads, followed by the development of an elaborate finite-element (FE) model which can accurately capture the experimental behavior in terms of strength, stiffness and failure mechanism. A full-scale version of the validated model, representing the bottom segment of a wind turbine tower under design loads, was finally employed for the conduction of a parametric analysis, as regards the structure's geometry and material properties, and the investigation of the sandwich concept's possible advantages over a conventional steel structure. Owing to the synergy between the steel tubes and the grout core, the composite specimens almost reached their plastic moment capacity, premature buckling was prevented, and ductility was preserved, despite the significantly high diameter-to-thickness ratio of the steel tubes and the thin grout core. Although performance deteriorates as the diameter-to-thickness ratio of the two steel tubes increases, the relative advantage of the sandwich tower over a plain steel one becomes more prominent, especially when high-strength grout is used. It is thus demonstrated that a sandwich-type shell comprising a thin layer of grout may improve a wind turbine tower's load capacity, stiffness and stability without increasing the total amount of steel, nor extending its base diameter beyond transportability-related restrictions.

Evolution regularity of temperature field of active heat insulation roadway considering thermal insulation spraying and grouting: A case study of Zhujidong Coal Mine, China

Abstract To study the active heat insulation roadways of high-temperature mines considering thermal insulation and injection, a high-temperature −965 m return air roadway of Zhujidong Coal Mine (Anhui Province, China) is selected as a prototype. The ANSYS numerical simulation method is used for the sensitivity analysis of heat insulation grouting layers with different thermal conductivities and zone ranges and heat insulation spray layers with different thermal conductivities and thicknesses; thus, their effects on the heat-adjusting zone radius, surrounding rock temperature field, and wall temperature are studied. The results show that the tunneling head temperature of the Zhujidong Mine is >27°C all year round, consequently causing serious heat damage. The heat insulation circle formed by thermal insulation spraying and grouting can effectively alleviate the disturbance of roadway airflow to the surrounding rock temperature field, thereby significantly reducing the heat-adjusting zone radius and wall temperature. The decrease in the thermal conductivities of the grouting and spray layers, expansion of the grouting layer zone, and increase in the spray layer thickness help effectively reduce the heat-adjusting zone radius and wall temperature. This trend decreases significantly with the ventilation time. A sensitivity analysis shows that the use of spraying and grouting materials of low thermal conductivity for thermal insulation is a primary factor in determining the temperature field distribution, while the range of the grouting layer zone and the spray layer thickness are secondary factors. The influence of the increased surrounding rock radial depth and ventilation time is negligible. Thus, the application of thermal insulation spraying and grouting is essential for the thermal environment control of mine roadways. Furthermore, the research and development of new spraying and grouting materials with good thermal insulation capabilities should be considered.

Shield tunnel grouting layer estimation using sliding window probabilistic inversion of GPR data

The ground penetrating radar (GPR) is an effective tool to detect the grouting layer behind shield tunnel linings, yet to estimate the thickness from GPR data is always difficult. We herein present a probabilistic inversion method to infer the grouting layer thickness together with its relative permittivity and electric conductivity values from GPR waveform data. This method uses a sliding window and Markov chain Monte Carlo (MCMC) simulation with Bayesian inference to explore the posterior distribution of model parameters. The inversion results of a synthetic example demonstrate that the proposed method successfully estimates the grouting layer thickness. We also investigate the impact of the modeling error on the inversion results, and use a modified likelihood function to eliminate the modeling error. With the modeling error corrected, the posterior model parameters converge correctly to their true values, and the associated uncertainties are quantified.

Experimental evaluation of column base connections composed by different grout types subject to shear

The column base connection is responsible for transferring the superstructure actions to the foundation and consists, typically, of a base plate and threaded steel bars or anchor rods. A grout layer is used for filling the clearance between the base plate and the top of concrete block, usually composed of a fluid-based hydraulic cementitious material with specific mechanical properties as high strength, negligible shrinkage, brittleness and delayed curing. Epoxy-based materials may be used as a more efficient material on applications with impact and dynamic loads or when a quick cure is required but as it is a recently developed material, its adoption occurs empirically. There are few studies about the use of this material in base column connections and mainly about its contribution to shear resistance due to the higher strength of this material. The international codes of steel and composite structures do not provide design guidance for the application of this material in base connections. Because of this lack of information, this work presents an experimental campaign about the behaviour of regular column bases, with a pre-installed steel anchor rod and grout layer composed of cement and epoxy materials, subject to monotonic shear forces.

Failure analysis and design of grouted fibre-composite repair system for corroded steel pipes

Grouted fibre-reinforced composite stand-off sleeve repair is a light-weight and easily deployable repair system for steel pipelines with localised metal loss. The effectiveness of this type of repair system is dependent on the load transfer through the grout layer, which is weaker than neighbouring components and susceptible to failure due to stresses developed from applied internal pressure. In this study, three dimensional (3D) Finite Element Analyses (FEA) of a full-scale pipe with different levels of metal loss were implemented to evaluate the failure behaviour and capacity of grouted composite repair system. Steel pipes with a localised defect ranging from 20% to 80% metal loss and repaired using two infill grout systems reinforced with carbon and glass sleeves of different thicknesses were considered. The results indicated that the performance of the repair system is governed by the tensile cracking of the infill grout. A thicker sleeve and higher tensile strength grout delivers higher pipe capacity in the repair system. On the other hand, a high modulus grout provides a more effective load transfer from steel to sleeve. Using a high tensile strength grout, the composite repair system can restore the capacity of the steel pipe with defect up to about 70% metal loss.

MCMC approach for shield tunnel grouting layer estimation using ground penetrating radar

Ground penetrating radar (GPR) has been suggested as an effective tool for evaluating the grouting layer behind shield tunnel linings, yet the estimation of the grouting layer thickness is usually difficult. In this paper, we propose a probabilistic inversion method to evaluate the grouting layer using GPR images. This method uses a sliding window along the GPR scan axis combined with a Markov chain Monte Carlo (MCMC) simulation with Bayesian inversion to infer the grouting layer thickness together with the relative permittivity and electric conductivity. We illustrate this approach using a synthetic GPR experiment that simulates grouting layer detection in a shield tunnel along the longitude direction. A sliding window with a width of 0.2 m is used to estimate the model parameters and is moved along the scan axis with a step size of 0.2 m after each inversion. The results demonstrate successful estimation of the grouting layer thickness and its relative permittivity and electric conductivity by the proposed method. Moreover, this method is capable of quantifying uncertainties in the inversion results.

Study on Comprehensive Treatment Technology of High-speed Railway Passing Through Giant Karst Tunnel

In the mountainous areas of Southwest China, a karst landscape is well developed. There, exposed giant karst caves in the construction of high-speed railway tunnels cause great construction difficulties and safety risks for the tunnel crossing. In this paper, the study object is the project on giant karst cave of the Qianjiang–Changde railway high-mountain tunnel. After the karst cave was revealed, unmanned aerial vehicle detection, three-dimensional laser scanning, and blasting vibration monitoring were used to study the stability of the karst cave. It was found that the karst cave has a higher risk of falling rocks. On the basis of careful consideration of construction, operation safety, and economy, the “backfill cave ballast + grouting to reinforce on the upper part” scheme was determined for the treatment of the karst cave. During the process of disposal, the surface and layered settlement of backfill were monitored, in which it showed that the surface settlement control was reasonable, and the settlement mainly came from the bottom of the grouting layer, the top of non-grouting backfill, and original accumulation. To prevent the risk of falling rocks, we performed permanent safety protection of the wall and the roof for the karst cave and temporary safety protection of the mobile scaffold. Finally, the backfill treatment of the giant karst cave of high-mountain tunnel was smooth, the settlement after construction was controllable, and it met the design requirements.

Groundwater flow below construction pits and erosion of temporary horizontal layers of silicate grouting

Injection of silicate grouting materials is widely used to create temporary horizontal layers for reducing inflow of groundwater at construction sites, in regions with shallow water tables. The erosion of a grouting layer was investigated by means of analytical solutions for groundwater flow and transport within a pit after construction finished. Erosion is assumed to occur by dissolution of the temporary injection layer and subsequent advective transport. Thereby, the hydraulic conductivity changes with time. This paper presents novel analytical solutions and approximate solutions for the major fluxes in the construction pit as a function of the domain settings, aquifer gradient and hydraulic conductivity. In addition, the mass flux and the dilution ratio of erosion-related components leaving the construction pit and entering the aquifer are quantified. Derived solutions are verified against numerical simulations. A sensitivity study shows the impact of domain settings on fluxes and dilution ratio. The results confirm that mass flux of grout components increases with ongoing erosion. Thus, its effect on groundwater quality increases with time after construction ceased.

Spatial Variability of Grouting Layer of Shield Tunnel and Its Effect on Ground Settlement

This study aims to investigate the effect of the spatial variability of grouting-layer thickness on ground-surface settlement caused by shield tunneling and to provide a rational prediction method. The spatial characteristics of grouting layers were obtained based on statistical analysis. The random finite element method was used to study the effect of spatial variability of different parameters on ground-surface settlement. Simulation results indicate that the spatial variability of the grouting layer has a negative impact on ground settlement. The surface settlement will be underestimated without considering the spatial characteristics of the grouting layer. Thus, a reliable prediction approach of the maximum ground settlement was proposed to control the construction quality.

3D numerical investigation of the coupled interaction behavior between mechanized twin tunnels and groundwater – A case study: Shiraz metro line 2

Mechanized tunneling method using Tunnel Boring Machine (TBM) is being extensively employed in urban areas, especially when excavation takes place underneath the groundwater table. In this study, three-dimensional coupled Finite Element Analyses (FEA) have been performed to investigate the interaction mechanism between mechanized twin tunnels construction of Shiraz metro (line 2) and groundwater. Firstly, two soil constitutive models (Mohr-Coulomb and Modified Cam-Clay model) of Shiraz lean clay are validated against drained triaxial compression test data. Varying the permeability of the grout layer within the specified range, the base numerical model is then calibrated by the field data of ground surface settlements. Parametric studies are conducted subsequently to evaluate the effects of influencing factors involved in the coupled FEA of twin tunnels, including the drainage boundary condition of the grout layer, the position of groundwater level, and the rest interval between excavations of twin tunnels. The numerical results indicate that the ground surface settlements and internal forces of existing segmental lining are greatly influenced by the drainage condition of the grout layer. Also highlighted is the marked effect of the drainage condition of the grout layer in the numerical prediction of the interaction behavior between mechanized twin tunnels and groundwater in different cases of the groundwater level and the rest interval between excavations of twin tunnels.

Time-Frequency Analysis of Impact Echo Signals of Grouting Defects in Tunnels

Abstract—Defects in the grouting layer are hidden problems of underground engineering quality, while it plays an important role in the stability of the overall structure of the tunnel segment, the earth pressure transmission and impermeability. There is no accurate means for the detection of the grouting layer so far. As a non-destructive testing method with single detection surface, the impact-echo method is widely used in the detection of cracks, delamination, voids, etc. in concrete structures. In this paper, the impact-echo method was used to detect the grouting defect in grouting-segment structure. Combined with the finite element and the test structure, the signal was analyzed in the time-frequency domain. The results show that the finite element results are in good agreement with the experimental results and the accuracy of frequency distribution characteristics results meets the engineering needs. The time-frequency analysis can provide a foundation for the qualitative judgment of defects.

Study on the long-term performance of cement-sodium silicate grout and its impact on segment lining structure in synchronous backfill grouting of shield tunnels

Synchronous backfill grouting is an important procedure in the construction of shield tunneling. The effect of grouting directly influences the settlement of the stratum and the stress state of the segments structure. During the construction of shield tunnels in rock mass, problems such as cutterhead deadlocking, segments floating and crack, surface subsidence, etc. would occur due to the buoyancy from synchronous backfill grouting. The cement-sodium silicate grouting can solve the above mentioned problems effectively, but meanwhile, its durability cannot be guaranteed, thus so far it has hardly been adopted in synchronous backfill grouting of shield tunnels. In the present paper, the long-term performance of cement-sodium silicate grout and its impact on segment structure in the backfill synchronous grouting during shield tunneling are systematically studied through theoretical analysis, laboratory tests, micro-analysis and numerical calculation. An evaluation method for long-term performance of cement-sodium silicate grout based on the meso-structure is proposed. Distribution form of reaction products of cement and sodium silicate grout and its change rule with the dosage of sodium silicate in cement-sodium silicate grout is revealed through the observation of meso-structure. The reduction factor of mechanical properties of cement-sodium silicate grout after degradation of the reaction products of cement and sodium silicate solution is derived with the help of stochastic finite element numerical calculation. The results reveal that when the proportion of cement and sodium silicate solution is within a certain range, the amplifications of both the internal force and deformation of segment structure are very small, even if grouting layer loses effectiveness completely. The maximum crushing stresses on the grouting layer after degradation is less than the minimum residual compressive strength, which can meet the practical engineering needs and guarantee the safety of the tunnel. Therefore, cement-sodium silicate grout is suitable for synchronous grouting in shield tunneling.