Two-component Grout Research Articles

Durability of Two-Component Grout in Tunneling Applications: A Laboratory Test Campaign

Today, two-component grout is the most widely used backfilling technology in shielded mechanized tunneling. Despite its intensive use, however, very scant information pertaining to the durability of this material is available in the scientific literature. In this work, the aging of two-component grout is studied by curing grout samples using three different modalities. Furthermore, the action of air on two-component grout is studied by assessing the dehydration process, which is a phenomenon that occurs when the material is cured without being completely embedded in soil/rock. Uniaxial compression tests and three-point flexural tests have been carried out for mechanical characterization. The results reveal that in a curing environment made of sand, a moisture of 5% is sufficient to guarantee correct curing of the grout and extend the mechanical performance to three years, whereas the action of air is potentially dangerous, since the grout suffers strongly from dehydration. Despite this dehydration process, however, the mechanical performance of the grout also tends to increase for samples cured under the action of air until a very high level of cracking and shrinkage is reached. A discussion of the limitations on the uniaxial compression strength as the main mechanical parameter for the characterization of two-component grout concludes the work.

LABORATORY INVESTIGATION OF THE EFFECT OF SODIUM SILICATE AND BENTONITE ON THE MECHANICAL PROPERTIES OF THE GROUT BEHIND THE SEGMENT IN MECHANIZED EXCAVATION

Nowadays, the use of Tunnel Boring Machines (TBM) in tunnelling has increased in urban environments. One of the effective parameters in the excavation process is the use of grout behind the segments to prevent ground settlement and penetration into the tunnel. The investigation of the effects of two-component grout (bentonite and sodium silicate) on the mechanical properties of the grout plays a crucial role in mechanized excavation. Therefore, this article aims to investigate the effect of various parameters on the properties of the two-component grout. Eight different mixing designs were considered in this research. Gel-time tests, viscosity test, water bleeding test, uniaxial compressive strength tests (UCS), and direct shear tests were conducted for each mixing design. The UCS tests were performed for eight mixing designs and at four different ages of the grout, while the direct shear test was conducted for five mixing designs at the age of one day. The results showed that increasing the sodium silicate content from 4% to 9.4% reduced the Gel-time to 7 seconds, and increasing the bentonite content from 2.3% to 4.58%, increased the marsh funnel time to 12 seconds. The uniaxial compressive strength of the grout increased to 0.682 MPa at the age of 28 days. Finally, by conducting the direct shear test on the grout and obtaining the parameters of cohesion and internal friction angle, it was determined that these two parameters depend on the values of bentonite and sodium silicate, and they change with the increase or decrease of these grout components.

The role of bentonite in two-component grout: A comparative study

Two-component grout is the most used backfilling technology in shielded mechanised tunnelling. Bentonite is an important ingredient in the production of component A, since it plays a key role in the mortar stabilisation. Furthermore, recent studies have highlighted its involvement in the mechanical and elastic performance of the hardened grout after short curing times, while no information is available for long curing times. This study proposes an innovative test campaign, based on a comparison between a standard two-component grout mix design (reproduced with 5 different bentonites) and a special mix design, produced without using the bentonite. This interesting comparison highlights the important role of the bentonite and its activation time in properties related to fresh grout (component A) and hardened grout. Assessments of bleeding, viscosity, unit weight, gel time, surface compression strength (SCS), uniaxial compression strength (UCS) and tensile strength (T0) have permitted a deep quantitative analysis that, undoubtedly, highlights the importance of bentonite in this widespread backfilling grout technology.

The characteristics of the two-component grout on the stress-state in segmental lining

The characteristics of the two-component grout on the stress-state in segmental lining

Elastic properties of two-component grouts at short curing times: The role of bentonite

Two-component grout is nowadays the material most used for the backfilling phase in tunnelling with a shield machine. The operative simplicity of the technology and the fast hardening reaction between the two components are the main reasons that have contributed to the intensive spread of the use of this backfilling technique all around the world. Although bentonite is one of the basic ingredients for the grout production, its effect on the elastic properties of the grout has not been completely investigated so far. In this work, six different two-component grouts and their elastic properties have been studied by means of geophysical measurements. The six grouts were characterised by the same mix design and five different bentonites, while one grout had no bentonite. The variation of the dynamic parameters over time was analysed at short curing times (up to 24 h). In detail, the shear wave velocity, the dynamic moduli and Poisson’s ratio were determined by means of the ultrasonic pulse velocity technique. The results show that the grouts with the bentonites have higher dynamic moduli than the grout without the bentonite. Moreover, a final analysis of the experimental data provided an analytical relationship to calculate the shear-wave velocity for each of the six grouts at any curing times.

Experimental study of the mechanical properties of two-component backfilling grout

In mechanised tunnelling, the filling of the annular gap behind the precast concrete segments is one of the essential operations. The main goal of filling this space is to reduce surface settlements and limit movements due to tunnel excavation in the soil mass. To achieve this aim, a two-component grout is often used to fill the annular gap. Determination of the amounts of ingredients in the two-component grout should be carried out in such a way that the injection materials will be able to fulfil the required performance and technical properties. In this study, laboratory tests were carried out to investigate two-component grout properties, such as flowability, bleeding, gelling time and uniaxial compressive strength. The effect of lateral pressure on grout resistance was studied according to real excavation situations. The influences of the grout ingredients and effective parameters such as bentonite and cement contents, water–cement ratio and the dosage of accelerator (sodium silicate) and accelerator ratio were also investigated.

Bentonite in two-component grout applications

Two-component grout is a cement-based material, currently the most used technology for backfilling in tunnelling applications. Despite its intensive, knowledge on this material is quite limited, especially as concern the role of ingredients and their effect on the properties of fresh mortar and hardened grout. In this work, an accurate and innovative test campaign focused on the role of the bentonite was performed. Three different bentonites were used. The activation of the bentonite and its effect on both mortar stability and grout strength was investigated with the purpose to recognise the bentonite parameters useful to select, at the design stage, the best bentonite according to the designers’ requirements. Swell index and Atterberg’s liquid limit were recognised as useful parameters for predicting results in terms of suitable bleeding and surface compression strength.

Improvement of two-component grouts by the use of ground granulated blast furnace slag

This work investigated the impact of a partial replacement of ordinary Portland cement (OPC) by ground granulated blast-furnace slag (GGBS) in two-component grouts. Maximum GGBS content reached 50 %wt of the binder. Fluidity, open time, bleeding behaviour, gel time, compressive strength development and durability with respect to sodium sulfate were assessed. The impact of a variation of the volumetric ratio between the grout base and the accelerator (components A and B) was also considered. The results showed that increasing GGBS content led to multiple benefits of grouts behaviour. At fresh state, the bleeding was limited without decreasing the flowability. At hardened state, it increased the 28-day compressive strength, and improved the durability of the grouts in water/sodium sulfate solutions when used at 16% of the binder mass (mix designs based on jobsite trials).

Creep behaviour of two-component grout and interaction with segmental lining in tunnelling

The complexity of the two-component grout behavior significantly affects the interaction between the support system and the tunnel. The loading of the filling material (and also of the segmental lining) takes place during the curing phase. At the end of it a creep phase develops which shows secondary deformations over time which result in a relaxation of the segmental lining and an increase in the deformation of the tunnel wall. In this work, a laboratory experiment campaign allowed to study the two-component material in detail during the creep phase. The typical trend of deformations over time, obtained for different stress load values and material curing age, was identified. The maximum stress was also evaluated which still allows to avoid the failure of the material over time, when a persistent state of stress is applied. The information obtained from the experimentation allowed to provide considerations on the support system-tunnel interaction, using the convergence-confinement method. The approach followed was then applied to a real case of a tunnel excavated in Northern Italy, for which it was possible to estimate the decrease in the load applied to the support system and the increase in deformations of the tunnel wall due to the creep phenomenon of the two-component material.

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.

Test Method for the Solubility Model of Physical Blowing Agent of Self-Expanding Polymer

This paper aims to present a solubility model of physical blowing agent (PBA) for a kind of commonly used self-expanding polymer on engineering. The self-expanding polymer contains Component A (isocyanate) and Component B (polyhydric alcohol, PBA, water, and catalyst). Component B grout of the polymer, which contains PBA, was heated to measure its temperature and volume variations. Based on the principle of mass conservation and Clapeyron equation, the solubility curve of PBA with respect to temperature was calculated. The solubility curve was then applied to simulate the foaming process. A two-component polymer grout foaming experiment was then carried out to verify the applicability of the measured solubility curve. The simulated changes of temperature and density with respect to time of polymer grout were analyzed and compared with experimental results. The error of both sets of curves is within 5%, which shows a good agreement among them and proves the feasibility of the solubility model. This study provides a relatively complete test and verification process for the solubility model of PBA, which lays a theoretical foundation for both the polymer grouting diffusion mechanism and engineering application.

Analysis of the behavior of the two-component grout around a tunnel segmental lining on the basis of experimental results and analytical approaches

The mechanized excavation of tunnels generally requires the injection of a grout material between the segmental lining and the ground. This material has an important role for the support system and governs the segmental lining loading, also because of the significant evolution of its mechanical characteristics over time. In this work, an accurate experimentation on the two-component material was conducted. Normally, hand mixing is performed in laboratory to test the mechanical performance of the two-component mix-design. In this paper an innovative instrumentation able to mix appropriately the components was used in order to obtain samples truly representative of the real site conditions. Laboratory compression tests performed on these samples allowed to accurately quantify the evolution of the strength and stiffness of the filling material during the setting time. In order to properly take into account the evolution over the time of the mechanical behaviour of the filling material and of the support system more generally, a new procedure was developed and illustrated in the work. The analysis procedure is based on the convergence-confinement method and is able to describe in some detail the reaction line of the support system during its loading. Due to the presence of the filling material, which improves its mechanical characteristics over time, the reaction line assumes a curved shape. The intersection with the tunnel convergence-confinement curve allows to determine the radial loads acting on the support system and to design the support system to ensure the stability of the tunnel. The innovative procedure was then applied to a real case of a tunnel excavated in Northern Italy, confirming the validity of the main project data adopted for segmental lining and filling material. A sensitivity analysis on the same case allowed to detect how some aspects of the support system loading have an influence, not only on the final radial load acting on the segmental lining, but also on the final stress state induced inside the filling material.

The influence of the two-component grout on the behaviour of a segmental lining in tunnelling

Filling material is present around the segment lining when a shielded Tunnel Boring Machine is used to excavate a tunnel. The two-component grout is becoming lately one of the most used filling materials. Its mechanical properties evolve over time. Unfortunately, there are not many studies in the literature on the specific mechanical characteristics of these materials. This work presents the results obtained from an extensive laboratory test campaign that allowed to fully characterize the two-component filling material during the setting period. In particular, the values of the stiffness and resistance parameters were obtained over time, where uniaxial compression tests and oedometer tests were carried out. A detailed study of the effect of the presence of the filling material on the behavior of the support system (segmental lining + filling material) was developed for two of the most widespread analytical methods for the analysis of the behavior of tunnels and structures of support: the convergence-confinement method and the Einstein and Schwartz method. Subsequent parametric analyses made it possible to consider the variability of the influencing parameters within the typical variability ranges obtained from the laboratory test campaign or known from the available scientific literature. From the study carried out, it was possible to note that it is necessary to consider the presence of the filling material in the evaluation of the stiffness of the support system, when using the convergence-confinement method to estimate the loads acting on segmental lining. In this regard, it is necessary to have a reliable estimate of the elastic modulus of the filling material in the period of loading of the segmental lining. On the other hand, the presence of the ring of filling material is negligible when evaluating the state of stress of the segmental lining with specific methods capable of considering the rock-support interaction. In particular, adopting the Einstein and Schwartz method, it is possible to define the bending moments and normal forces acting in the support structure, referring to the stiffness parameters of the segmental lining alone.

Cementitious Composites with High Compaction Potential: Modeling and Calibration.

There is an increasing need for the development of novel technologies for tunnel construction in difficult geological conditions to protect segmental linings from unexpected large deformations. In the context of mechanized tunneling, one method to increase the damage tolerance of tunnel linings in such conditions is the integration of a compressible two-component grout for the annular gap between the segmental linings and the deformable ground. In this regard, expanded polystyrene (EPS) lightweight concrete/mortar has received increasing interest as a potential “candidate material” for the aforementioned application. In particular, the behavior of the EPS lightweight composites can be customized by modifying their pore structure to accommodate deformations due to specific geological conditions such as squeezing rocks. To this end, novel compressible cementitious EPS-based composite materials with high compaction potential have been developed. Specimens prepared from these composites have been subjected to compressive loads with and without lateral confinement. Based on these experimental data a computational model based on the Discrete Element Method (DEM) has been calibrated and validated. The proposed calibration procedure allows for modeling and prognosis of a wide variety of composite materials with a high compaction potential. The calibration procedure is characterized by the identification of physically quantifiable parameters and the use of phenomenological submodels. Model prognoses show excellent agreement with new experimental measurements that were not incorporated in the calibration procedure.

Ultrasonic measurements for assessing the elastic parameters of two-component grout used in full-face mechanized tunnelling

The use of shield machines and instantaneous segment linings for tunnel construction is one of the most used tunnelling methods today. Despite a large number of applications in different tunnelling projects all around the world, knowledge of the behaviour of two-component grout is quite limited, mainly due to the fast hardening process that inhibits using the classic approach for concrete characterization. In the present work, an innovative approach based on ultrasonic measurements is introduced, aimed to characterize the elastic properties of this innovative backfilling material. Specifically, ultrasonic pulse velocity was applied to two-component grout samples to describe the interesting and fast evolution of the material from the mixing phase until 6 months of curing using geophysics parameters. The dynamic Young’s modulus (E) and the dynamic shear modulus (G) exhibited a clear increasing trend, starting from values of a few tens of MPa to final values equal to 1000 MPa and 340 MPa, respectively. The Poisson’s ratio (ν), close to the value of incompressible materials (0.5) at the short curing time, exhibited a decreasing trend, reaching roughly 0.445 after 3 months of curing.

Synthesis and characterization of eco-friendly alkali-activated industrial solid waste-based two-component backfilling grouts for shield tunnelling

The two-component grout consisting of liquid A (cement paste) and liquid B (accelerator) is often used for backfill grouting in shield tunnels. However, the traditional cement-sodium silicate (CS) grout not only consumes ordinary Portland cement, but also has the disadvantage of poor resistance to water corrosion. In view of this, this study explored the possibility of using industrial solid wastes as solid precursors to prepare a new eco-friendly two-component grout. Through a series of experiments, the effects of factors including the solid precursor composition of liquid A, the modulus of liquid B (sodium silicate), the volume ratio of liquid B to liquid A and the additive content on the properties of alkali-activated industrial solid waste (AAISW) based two-component grouts were investigated systematically. The gel time, flowability, bleeding ratio, mechanical strength and water corrosion resistance of AAISW grouts were tested and compared with those of the CS grout. It is found that the gel time of AAISW grouts can be adjusted in the range of tens of seconds to minutes. The flowability loss with time of liquid A of AAISW grouts is significantly less than that of liquid A of the CS grout. The AAISW grout has good stability and can achieve compressive strength comparable to or even higher than that of the CS grout. In addition, the water corrosion resistance of the AAISW grout is obviously better than that of the CS grout. The eco-friendly AAISW grout has obvious advantages over the CS grout in terms of performance and sustainability, so it has promising application prospects.

Void detection in two-component annulus grout behind a pre-cast segmental tunnel liner using Ground Penetrating Radar

Ground Penetrating Radar (GPR) is being considered as a potential non-destructive technique for ensuring complete annulus grout backfill behind pre-cast segmental tunnel liners. Current methods for ensuring grout backfill involve drilled verification holes through the waterproof liner. The Rondout bypass tunnel, in Newburgh, NY, where void formation behind the tunnel liner is possible due to high groundwater pressures, provided an example project to evaluate GPR capabilities. While the application of GPR for void detection in one component grouts behind tunnel liners has been well-documented, site specific calibration of the GPR equipment and the application to two-component grouts is necessary. Experiments were conducted on actual tunnel segments to determine the most appropriate antenna frequency that can penetrate through the steel-reinforced segments and produce the best resolution. Mock air and water voids were embedded within areas of complete grout behind the segment to demonstrate the GPR signatures. Steel reflectors buried within the grout provided indirect measurements of the electromagnetic (EM) properties of the two-component grout. All field results were compared against analytical evaluation and numerical models to validate void detection. The findings of this research allow for direct implementation of the GPR technique for detection of voids behind segmental tunnel liners with two-component grout backfill.

An Experimental Study of the Performance of Two-Component Backfilling Grout Used behind the Segmental Lining of a Tunnel-Boring Machine

Abstract How to fill the empty annular space behind the segmental lining of tunnels is considered one of the most important questions in mechanized excavation, of which the main aim is to minimize settlement on the earth surface. In addition, the grout is the agent that creates a suitable bed for the segment lining of the tunnel and helps with its tightening. There are different methods of filling the empty space. One of them, using excavation by Earth Pressure Balance-Tunnel Boring Machine (EPB-TBM), is the injection of two-component grout at suitable pressure to the back of the segment as the shield of the excavator moves ahead. The grout utilized has suitable mechanical characteristics and efficiency. The main properties of grout refer to bleeding, fluidity and the results of the Marsh funnel test (ability to pump grout), setting time, gelling time (to avoid grout washing out) and compressive strength of grout (to minimize settlement on the earth level). The present study attempts to review the effect of any constituent materials of two-component grout on the parameters. Consequently, different tests with various constituent materials on the properties of grout were conducted.

Numerical Study on Backfilling the Tail Void Using a Two-Component Grout

AbstractIn shielded mechanized tunneling, the annular gap caused by the tunnel boring machine (TBM) driving must be backfilled instantaneously using a suitable grout. A two-component grout composed...

The effectiveness of polymer adhesive in reduction of vibrations of structural members

In this paper, the idea of using polymer adhesive as a damping layer is proposed. An experimental study of two aluminium cantilevered beams has been conducted. One of them presents a plain cantilevered beam, while the second one considers two aluminium beams bonded with a polymer adhesive of different thickness (0,5; 1,2; 1,75; 3,1 and 5 mm). The polymer adhesive considered in the study is a specially designed flexible two-component grout, which has high damping properties. The aim of the study is to determine dynamic parameters, such as natural frequencies and damping ratios of both beams, based on the tests in which analyzed elements have been induced to vibrations by a modal hammer. The behaviour of the beams under different additional weight, installed at the end of elements, has been studied. The results of the study clearly show that the response of the composite aluminium beam with polymer adhesive inside is substantially different then the response of the plain beam. The application of polymer adhesive leads to significant increase in structural damping. Based on the results, the method of using the polymer adhesive can be considered as an effective one in reduction of structural vibrations.