Grouting Effect Research Articles

Experimental method and application of the slurry “diffusion-bleeding-seepage” of isolated overburden grout injection

Isolated overburden grout injection (IOGI) is a green mining method to control surface subsidence. Slurry water significantly influences grouting effectiveness and mining safety. This study establishes a three-dimensional visualization experimental system for slurry “diffusion-bleeding-seepage” to investigate the seepage law of slurry water. The system is composed primarily of a transparent box (1.2 m × 0.5 m × 0.25 m) and support, with the solid–liquid coupling seepage similar material and modules for mining, grouting injection, slurry pressure and displacement monitoring, overburden saturation monitoring, and water leakage monitoring of the working face. A similar material with good permeability and non-disintegration is obtained by hydrophilic, water absorption, and permeability tests. Grouting and mining are simulated by pulling acrylic sheets and pumping slurry. With the fly ash slurry entering the injection layer, the slurry undergoes water–cement separation, and the water bleeding is formed to seep into the similar material. The volumetric water content of the similar material is obtained by arranging multiple groups of volumetric water content sensors into the similar material. The corresponding saturation is obtained by theoretical calculation. The experimental system is used to simulate the seepage of slurry water in a high initial saturation overburden, and the characteristics of injection slurry diffusion and water bleeding are obtained. The profile distribution of seepage of slurry water is found to possess a semi-elliptical shape. Under the condition of high initial saturation, slurry water appears in the working face. The system provides a convenient method for further research of IOGI slurry water seepage.

Mechanism and Application of Layered Grouting Reinforcement for Fractured Coal and Rock Roadway

This paper takes the ZF3806 working face of Shuiliandong Coal Mine in Binxian County, Shaanxi Province as the engineering background. Aiming at the problems of the development of surrounding rock cracks and roof breakage encountered in the process of roadway excavation and support and based on the composite beam theory, the method of layered grouting reinforcement of roadways is proposed according to the deformation and failure of the roadway roof and the internal drilling conditions. At the same time, combined with the splitting grouting mechanism, the roadway is strengthened and supported by layered grouting of “shallow bolt grouting + deep cable grouting”. The “shallow” and “deep” form a complete and stable composite beam support structure. After grouting, the bending moments of “shallow” and “deep” support beams decrease by 20.78 × 106 N·m and 26.50 × 106 N·m, respectively. The support scheme is applied to the field test, and the grouting effect is analyzed and monitored. The research results show the layered grouting support scheme of “shallow bolt grouting + deep cable grouting” can significantly improve the structural integrity of the roadway roof. The displacement of the two sides is within the controllable range, and the support role of the bolt and cable is entirely played through grouting. The roof displacement of the roadway is reduced by 65% on average, and the bolt failure and steel belt fracture are significantly reduced, which effectively controls the deformation and damage of the roadway and reduces the maintenance cost of the roadway while ensuring safe mining. The study’s findings could be useful in treating broken surrounding rock in other coal mine roadways.

Experimental Study on the Shear Properties of Soil around Piles with Permeation Grouting

While post-grouting is frequently reported to improve the engineering performance of piles, the shear strength of the soil around piles is not well understood. To investigate the strengthening mechanism of soil around piles with permeation grouting, laboratory tests were carried out on homemade cement soil from the aspects of shear strength and microstructure characteristics. The evolution rule of the shear stress–shear displacement curve of grouting soil with different cement contents was analyzed, and the influence of grouting parameters on shear strength was explained. A composite exponential model describing the shear stress and shear displacement of permeation grouting silty clay was established. Furthermore, the influence of different cement content on changes in the microstructural characteristic parameters of the soil around piles was studied. The results show that penetration grouting has a positive effect on improving the shear strength of the soil around piles, and the failure mode of silty clay changed from elastic–plastic failure to brittle failure after grouting. Permeation grouting makes the particle structure denser, which limits the changes in pore arrangement and distribution. The shear failure of the soil around piles under permeation grouting obeys the Mohr–Coulomb criterion of failure. It is recommended to increase the grout diffusion radius during construction, considering the reinforcement effect of permeation grouting on the soil around piles.

Curtain Grouting Effectivity Analysis On Foundation Rocks In Blocks 37 – 40 In The Body Of Randugunting Dam, Blora Regency, Central Java

Blora Regency is a barren area in Indonesia and has drought disaster potential, to address those problems Indonesian Governments launched Randugunting Dam’s construction program. The research area was located at Block 37 – 40, Radugunting Dam, Japah District, Blora Region. Dam as a water retention building should have foundation rocks that are resistant towards seepage potential, therefore curtain grouting was conducted to seal geological fractures on the foundation rocks. The purpose of these research was to understand the seepage potential on foundation rocks, foundation rocks curtain grouting requirement, and curtain grouting effectiveness. Research method used were water pressure test (WPT) data analysis, in the form of water flow discharge data processed through calculation to produces Lugeon value (Lu). The Lugeon value (Lu) would be further analyzed to determine the curtain grouting effectiveness value. The result of the analysis shows that around 18.15% of the research area have seepage potential that was shown by medium (3 < Lu < 10) – high (Lu > 10) Lugeoun (Lu) value. After the curtain grouitng was conducted, it effectiveness value on Block 37 was 88.34% (good), on Block 38 was 81.43% (good), on Block 39 was 70,62% (good), and on Block 40 was 79.41% (good).

Pre-Reinforcement Mechanism and Effect Analysis of Surface Infiltration Grouting in Shallow Buried Section of Long-Span Tunnel

In order to solve the problem that the hole-forming rate of boreholes is low and it is difficult to reach the designed length when supporting a long pipe shed in loose stratum in a shallow buried section of a long-span tunnel, it is necessary to pre-reinforce the loose stratum in order to improve the strength and integrity of the surrounding rock. Relying on the grouting project of the shallow buried section at the exit of Botanggou tunnel, it is assumed that the grouting material is Newtonian fluid and the steel floral tube shows cylindrical infiltration and diffusion. Through the analysis of the structural characteristics of the injected stratum, the conceptual model of infiltration grouting is established. Twelve groups of test slurry were prepared with ordinary Portland cement and ultra-fine cement, and through the analysis of the slurry parameters of each group, ordinary Portland cement slurry was selected with a water–cement ratio of 1:1 plus 3% water glass to strengthen the gravel layer, and ultra-fine cement slurry with a water–cement ratio of 1:1 plus 3% water glass and 0.3% polycarboxylate superplasticizer to strengthen the fully and strongly weathered porphyritic granite layer. Through the on-site single-hole grouting test and combining with the empirical formula, the maximum diffusion radius of single-hole infiltration grouting is calculated, and the sliding width of the sidewall is deduced using Terzaghi theory. To ensure the grouting effect, the 5 m expansion of the excavation profile is taken as the grouting range. Grouting construction adopts the overall order of periphery and then interior, and three-sequence opening and grouting are adopted in the same row of grouting holes, which can effectively prevent grouting running and grouting. For the strata treated by surface grouting, the construction of the long pipe shed is smooth and reaches the designed length, and there is no large deformation of the surrounding rock when excavated using the CD method. The treatment effect is analyzed by the P-Q-t control method, excavation observation method, and deformation monitoring method. The results show that the injected stratum is fully infiltrated and gelled, forms an obvious grouting stone body, the integrity and strength of surrounding rock are obviously improved, and the convergence values of the tunnel surface, vault subsidence, and clearance do not exceed the alarm value of 60 mm. The research results provide some awareness and understanding of the grouting pre-reinforcement of loose stratum in a shallow buried section of a long-span tunnel in the future.

Application of Long-Range Cross-Hole Acoustic Wave Detection Technology in Geotechnical Engineering Detection: Case Studies of Tunnel-Surrounding Rock, Foundation and Subgrade

The adverse geological conditions of soil cave, karst cave and goaf in deep foundation directly affect the safety and economy of geotechnical engineering construction. It is a difficult problem in geotechnical engineering detection to detect the distribution of bad geological conditions efficiently and accurately. Aiming at the problems of short penetrating distance and low resolution of cross-hole acoustic wave detection in rock-soil mass, based on the characteristics of acoustic wave propagation in rock and soil layers and comprehensively utilizing the spark source and data acquisition device, a long-distance cross-hole acoustic wave detection technology is proposed. According to the indoor concrete model test and field tests of geotechnical engineering, the applicability of the long-distance cross-hole acoustic wave detection technology in the detection of geotechnical structure and adverse geological phenomena under complex geological conditions is verified. The results show that acoustic wave CT imaging can accurately detect the cavities in the indoor concrete model test. In addition, the field tests of the grouting effect of tunnel-surrounding rock, high-rise building foundation and subgrade further verify the rapidity, accuracy and intuitiveness of the long-distance cross-hole acoustic wave detection technology. This work provides a reference for eliminating the potential safety problems caused by adverse geological conditions and similar geotechnical engineering investigation.

Analytical Solutions of Steady a Seepage Field for Deep-Buried Tunnel with Grouting Ring Considering Anisotropic Flow

Difficulties related to seepage are frequently encountered in tunnel design and construction, especially in deep-buried tunnels. Nowadays, analytical solutions of steady seepage fields for deep-buried tunnel usually assume that the surrounding rock mass is homogeneous. In this study, analytical solutions of a steady seepage field for a deep-buried tunnel with grouting ring considering anisotropic flow are proposed. The proposed analytical solutions are verified by numerical simulations and parameter analysis are carried out. Results show that the seepage field of surrounding rocks around the deep buried circular tunnel is no longer uniformly distributed and presents elliptical distribution. The change of permeability coefficient of the lining structure has a great influence on the hydraulic head when the difference between permeability coefficient of lining structure and surrounding rock is not very large. The results show that the size of the grouting ring has more significant influence on the grouting effect.

Analysis of Surrounding Rock Control Technology and Its Application on a Dynamic Pressure Roadway in a Thick Coal Seam

The deformation control of roadways surrounded by rock in the fully mechanized amplification sections of extra-thick coal seams is problematic. To analyze the failure and failure characteristics of a support frame, as well as the deformation and failure processes of the surrounding rock, through theoretical analysis and industrial tests, the deformation and support conditions of a return airway of a fully mechanized caving face in an extra-thick coal seam in the Yangchangwan Coal Mine, in the Ningdong mining, area were examined. Combined with limit equilibrium theory and roadway section size, the width of the coal pillar of the return air roadway at the 130,205 working face was calculated to be 6 m. The layout scheme and implementation parameters of roof blasting pressure relief, coal pillar grouting modification, and bolt (cable) support were designed. Based on the analysis, a “Coal pillar optimization–roof cutting destressing–routing modification–rock bolting” system for surrounding rock control in synergy with the fully enlarged section mining roadway in the extra-thick coal seam was proposed, and the deformation of the surrounding rock was monitored, along with the stress of the support body and the grouting effect on the site. Field experiments show that after the implementation of the surrounding rock control in synergy with the roadway, the maximum subsidence of the top plate was 55 mm, the maximum bottom heave of the bottom plate was 55 mm, the maximum values of the upper and lower side drums were 30 mm and 70 mm, respectively, and the breaking rate of the bolt (cable) and the deformation of the surrounding rock of the roadway was reduced by more than 90% and 70%, respectively. The effective performance of the coal pillar grouting was observed as well. Field practice of the roadway surrounding rock control in the synergy method indicated that rock deformation was effectively controlled, and the successful application of this technology was able to provide reliable technical and theoretical support for the Ningdong mining area and mines with similar conditions.

Mechanical behavior of secondary lining vault void and mold grouting repair considering contact effect

A void in a tunnel’s secondary lining vault endangers traffic safety, as it affects the mechanical properties and the durability of a tunnel’s structure. In this paper, the damage due to a void and the repair effect of mold grouting were studied. In order to consider the contact effect of the waterproof layer, an interface element was used to connect the secondary lining and the primary lining, and the connection stiffness was limited. On this basis, the effect of a void on the mechanical behavior of the secondary lining was studied by numerical simulation. Then, a numerical model of the contact surface between the grouting body and the molded concrete was established and combined with a typical tunnel model. By changing the bonding strength of the contact surface, the relationship between the mechanical behavior of the grouting body and its bonding performance was analyzed, and its influence on the whole lining is discussed. Finally, the effect of mold grouting is discussed on the basis of field tests and the monitoring results. The results showed that the risk of a crack or even failure of the secondary lining increases significantly with the expansion of a void. Considering the contact effect of the waterproof layer, the connection stiffness between the secondary lining and the primary lining was significantly reduced, and the secondary lining showed more obvious independence and integrity. The insufficiency of the bonding strength between the grouting body and the molded concrete led to the loss of shear strength, and the failure would start from the edge of the grouting body and develop toward the middle. In the cases of class III, IV, and V surrounding rock, the recommended shear strength of the contact surface is about 0.65 MPa, 0.85 MPa, and 1.10 MPa, respectively. The construction method of the mold grouting can guarantee the effective bonding between a grouting body and the molded concrete, so as to avoid cracks, block falling, collapse, and other damage.

Effect of Fiber Content on Mechanical Properties and Microstructural Characteristics of Alkali Resistant Glass Fiber Reinforced Concrete

Owing to its enhanced strength, ductility, and resistance to harsh environments, increasing research attention has been paid to alkali-resistant glass fiber reinforced concrete (ARGFRC). This paper presents experimental studies concerning the effects of fiber content on the mechanical properties and microstructural characteristics of ARGFRC. The amount of glass fiber was considered at levels of 0.0, 0.3, 0.5, 0.8, 1.0, 1.3, and 1.5% of the concrete volume. The compression, flexural, impact resistance, scanning electron microscopy, and energy dispersive spectroscopy tests were conducted. The flexural load-deflection curve, flexural strength, flexural toughness index, flexural fracture energy, postcracking stiffness, postpeak stiffness, and impact resistance energy absorption were obtained. Then the changing law affected by fiber content on these mechanical properties was further analyzed, and the corresponding equation was fitted. When fiber content was 1.5%, the flexural toughness index I5, I10, and I20 values were 4.0, 5.9, and 8.9, respectively, and increased by 3.0∼7.9 times. Glass fiber incorporation could increase the ductility and delay the brittle failure when the fiber content reached 0.8%. The largest postcracking stiffness was calculated at 36.174 kN/mm with a fiber content of 0.8%. The higher the fiber content, the larger the postpeak stiffness of the tested beams. Impact resistance test results demonstrated that the optimum fiber content was 1.3%. As the fiber content increased, the effect of the concrete grout on the fiber packaging decreased, according to the scanning electron microscopy analysis. The energy dispersive spectroscopy observation proved that adding a certain fiber content did not affect the concrete hydration reaction.

Grouting Treatment and Parameters Optimization in Watery Karst Areas of High Speed Railway Tunnel Based on Comprehensive Geological Forecast: A Case Study

Based on the failure of the initial grouting scheme in tunnel engineering, an integrated geological forecasting system incorporating an industrial endoscope was used to detect watery karst areas in this tunnel. Numerical simulations were used to analyze the change patterns of arch top settlement, arch bottom bulge, and water surge in the tunnel under different grouting thicknesses. Compared to the displacement of the support structure, curtain grouting thickness is mainly reflected in reducing the amount of water surge. When the grouting thickness exceeds 5 m, the water-stopping effect of the tunnel is almost unchanged. Finally, a grout thickness of 5 m and a grout length of 25 m were selected as the grouting range for this project. During grouting, the combination of the three grouting techniques can effectively solve the problems of high water surges and difficult hole formation. The principle of “combination of exploration and injection” was followed to obtain real-time geological information and optimize the subsequent grouting plan. After the grouting, the grouting evaluation results and the field construction conditions showed that the grouting effect was good.

Precise application of grouting technology in underground coal mining: water inrush risk of floor elimination.

Many coal mines in China suffer from the Ordovician limestone (OL) and Carboniferous limestone (CL) containing water inrush frequently due to the complex geology condition; water inrush has become a serious disaster in coal mining. To prevent water-bursting disaster from the floor of mine and cutting down deaths and economic loss, a grouting method for limestone fracture aquifer has been widely adopted. In this paper, a time-dependent empirical grouting model considering (1) time-dependent behavior of the injected slurry, (2) response of the rock, and (3) interaction between the slurry and rock was proposed to describe the slurry diffusion mechanism in rock fracture. Aiming at the problem of water disaster prevention of a coal seam floor in 16,104 working face of Luxi coal mine, that was, the grouting failed to seal the water flow channel of aquifer, the causes of the failure of grouting for water sealing were analyzed. According to the aquifer parameters and model calculation results, a grouting scheme with a slurry diffusion radius of 20m and grouting pressure of 8MPa was proposed; 2 rounds of grouting were implemented, following the split spacing principle, to ensure that finer fractures can be sufficiently sealed. Finally, with the comparative analysis through the network parallel electrical method (NPEM) and the drilling exploration method for water-rich areas before and after grouting, it was verified that the grouting effect for floor limestone aquifer was good, and the grouting scheme proposed and the grouting pressure designed were reasonable. Results may provide reference to a karst fractured aquifer grouting project, as well as reduced the losing because of blindness and experience.

Injectability analysis of seawater-mixed magnesium phosphate cement slurry applied to a sand layer

Magnesium phosphate cement (MPC) is extensively used for construction and quick repairs owing to its high performance and good erosion resistance. This study aims to evaluate the injectability of seawater-mixed MPC slurry into a sand layer for grouting reinforcement. The setting time, fluidity, rheology, particle characteristics of MPC slurries mixed with freshwater and seawater, and the grouting effect are explored. The raw material composition and microstructure are also analyzed. The results revealed that the mass ratio of borax to magnesium (B/M) and magnesium to ammonium dihydrogen phosphate (M/ADP) plays a vital role in the setting time of seawater-mixed MPC slurries. Considering the hydration and rheological behavior of seawater-mixed MPC slurries, an optimal formulation is proposed, which incorporates fixed M/ADP, B/M, and W/C ratios of 2.5, 10%, and 0.2, respectively. Unlike cement-based grouts, MPC has no obvious flocculation effect, and seawater-mixed slurry has a greater viscosity, particle size, and longer setting times during initial hydration. Seawater-mixed MPC slurry has good pumpability as a grouting material; however, its injectability is slightly worse than that of freshwater-mixed slurry.

Formation Mechanism of “Large-Area Sweating” Water Seepage from Deep Mine Sandstone Pores

The groundwater in nonkarst areas can be divided into two categories: pore water and fracture water. Unlike fracture seepage, sandstone pore seepage in deep mines manifests as a large area of “sweating,” rather than an area of local “spray,” and is difficult to plug via conventional grouting methods. This study focused on pore seepage in deep mine sandstone to improve the grouting effect. Taking the deep mine sandstone in the southwest Shandong coal field, where “large-area sweating” seepage occurs, as the study object, this study examined the pore structure, petrological characteristics, physical properties, and grain sizes of the sandstone by analyzing experimental data from thin sections and scanning electron microscopy samples. The formation mechanism of the “large-area sweating” seepage was then analyzed. The range of permeability in which “large-area sweating” seepage may occur in the sandstone was discussed. The results indicate that the process of “large-area sweating” seepage in deep mine sandstone can be divided into a matrix softening stage, a matrix erosion stage, and a “large-area sweating” water seepage formation stage. According to the case analysis on the “large-area sweating” seepage in the Tangkou coal mine of the Southwest Shandong coalfield, the lower limit of permeability of the “large-area sweating” sandstone is approximately 0.25 mD. Thus, this type of seepage can occur in deep mine sandstone with a permeability of greater than 0.25 mD and affect typical mining production. The results of this study provide information about the formation mechanism of “large-area sweating” water seepage from sandstone pores and can theoretically inform the development of a new permeation grouting technique.

A Comparative Study on Steady-State Water Inflow into a Circular Underwater Tunnel with an Excavation Damage Zone

Excavation damage zones that occur around tunnels usually lead to a change in rock permeability, which has an impact on the water inflow into tunnels and even induces water inrush disasters. For a better understanding of the effect of the excavation damage zone, analytical solutions that consider the excavation damage zone are developed based on the review and modification of the solutions that consider linings and grouting circles. Then, both analytical solutions and the finite element method are applied to estimate the water inflow, and the results are in good agreement. The effect of the excavation damage zone on water inflow is analyzed based on an impact factor of the excavation damage zone and evaluated in a real engineering case, and the seepage-preventing effects of grouting are discussed. The results reveal that the water inflow increases with increasing permeability and thickness of the excavation damage zone and that there is a limit for the effects of the excavation damage zone. In addition, the effect is stronger for underwater tunnels with small water inflows and stabilizes gradually as the magnitude of water inflow increases. The increase in the impermeability and thickness of the lining and grouting circle can reduce the effect.

Rate-dependent mechanical behavior of jointed rock with an impersistent joint under different infill conditions

Transition in the rate-dependent mechanical response of rock was investigated due to the presence of impersistent joint with different infill conditions. Four types of samples, i.e. intact, jointed with no grouting, jointed and grouted with cement, and jointed and grouted with epoxy, were fabricated using model material. A series of dynamic split Hopkinson pressure bar (SHPB) tests was conducted on prepared samples with strain rates varying between 53–130 s −1 along with static uniaxial compression tests (10 −4 s −1 ). Progression of fracture/failure along samples was monitored using high-speed imaging and digital image correlation (DIC). Strength was observed to be significantly lower for jointed samples as compared to intact samples. However, the increasing trend of strength with strain rates remained similar for all types of samples. Epoxy was observed to be a better grout due to greater improvement in the strength of epoxy grouted jointed samples than cement grouted samples under both static and dynamic conditions. Significant changes were observed in fracture behavior (initiation, pattern and mechanism) with strain rate for intact and jointed unfilled/grouted samples. Fracturing was dominated by shear and tensile cracks at high strain rates compared to tensile cracks at low strain rates in all samples. Unlike static loading conditions, the location of cracks initiation shifts away from joint tips with increasing strain rate and depending upon existing infill conditions (unfilled/grouted). • The effect of an impersistent joint on the rate-dependent strength and fracturing behaviour of jointed rocks is investigated and compared with that of intact rocks. • The effect of joint grouting on the rate-dependent behaviour of jointed rocks is investigated and compared with that of jointed rocks with clean joints. • The efficiency of different grout materials in the improvement of the dynamic response of jointed rocks is investigated. • Suggestive guidelines are provided for the selection of grout materials for jointed rocks under static and dynamic conditions.

Performance of box-shaped column connection achieved with local grouting and bolts

To prevent the traditional box-shaped column flange connection from affecting the facade of the overall structure, this study proposed a box-shaped column connection achieved by local grouting and bolts. One integral box-shaped column specimen and two box-shaped column connection specimens were designed. The seismic performance of the connection and the influence of local grouting on the mechanical performance of the connection were studied. The failure phenomenon of the specimen was observed, and the mechanical performance of specimens, such as hysteretic behavior, bearing capacity, stiffness degradation, ductility, and energy dissipation capacity were examined. Results are as follows: the failure mode of the integral box-shaped column specimen and the specimen connected by local grouting and bolts is plastic hinge failure; the effect of local grouting can improve the integrity of the connection and obtain good energy dissipation capacity; the effect of local grouting can increase the bearing capacity of specimen by 24.84% and reduce the bolt tensile force by 34.37%; the steel connector at the column–column joint prevented the buckling deformation of the box-shaped column; the ductility is increased by 22.06%; no slip occurred between the upper and lower steel connector. Therefore, the new joint is safe and reliable. Through numerical simulation analysis, the research results show that the joint can be equivalent to rigid connection. The peak bearing capacity of the box–column joint is checked according to the Code for Seismic Design of Buildings: GB50011–2010. The calculation results are consistent with the experiment results.

Study on Mechanical Properties of Permeable Polymer Treated Loess.

The reinforcement and durability of loess are of great importance for road performance. In this study, a self-designed grouting system and newly permeable polymers were adopted to investigate the mechanical properties and durability of solidified loess (SL), considering different dry densities and water contents. The unconfined compression test and piezocone penetration (CPTU) test were used to examine the mechanical properties. The mechanism of the loess solidified by permeable polymer was analyzed from the micro-level by SEM, MIP, and XRD tests. The test results show that the effect of polymer grouting is obvious, the unconfined compressive strength (UCS) of the SL after grouting is as high as 3.05–5.42 MPa; it is 11.83–20.99 times that of unsolidified loess (UL). The UCS of the SL after grouting is inversely proportional to the dry densities and water contents. After 56 days of immersion, the SL still shows a high compressive strength. The additional erosion of the SL was not caused by the salt solution; the durability is significantly better than that of cement mixing soil. The sensitivity of various factors on the UCS of the SL are service environment > water content > dry density. The SEM tests clearly show that the gel formed by the reaction of the polymer with water on the surface of soil particles makes the bond of soil particles tighter. It can be observed from the MIP test that the cumulative mercury of SL was 0.115 mL/g, which was 33.72% of UL (0.341 mL/g), and the cumulative mercury of SL after immersion in water and salt solutions was 0.183 mL/g and 0.175 mL/g, which was 53.7% and 51.3% of UL (0.341 mL/g), respectively. The XRD results show that there are no other new mineral components produced after grouting and the spacing between crystalline planes decreases, which proves that permeable polymer grouting makes the soil denser and does not erode the soil particles.

Molecular Dynamics Simulations of Polymer Grouting Material: Its Mechanical Behavior under Uniaxial Tension, Cyclic Tensile Loading, and Stress Relaxation

At present, polyurethane (PU) has been extensively used as a grouting material in civil engineering. The mechanical properties of PU are the key to achieving the desirable grouting effect. This study presents the research results of the mechanical behavior of PU matrix under tensile, successive cyclic tensile, and stress relaxation at the nanoscale, using the coarse-grained molecular dynamics simulation method. The influences of the number of molecule chains and strain rate on the tensile mechanical properties are discussed, and the tensile deformation mechanism of PU matrix is revealed. The tensile strength of PU matrix is independent of loading path, and after yielding, the strain of PU matrix contains the elastic strain, plastic strain, and viscous strain. In the stress relaxation process, the evolution of the axial stress is mainly caused by the varied van der Waals interactions. The stress relaxation behavior of PU matrix can be described by the viscoelastic model consisting of one elastic element in parallel with one Maxwell element.

Research on reuse of silty fine sand in backfill grouting material and optimization of backfill grouting material proportions

Silty fine sand is a common muck in shallow urban tunnels, and the reuse of on-site muck resources is an urgent need in the field of shield tunneling. A shield tunneling section of Nanjing Metro Line 7 in a silty fine sand formation was analyzed in this paper. Combined with SPSS multiple regression analysis and MATLAB multiobjective planning tools, X-ray diffraction technology and laboratory tests were used to optimize the ratio of muck grouting liquid. The feasibility of silty fine sand as a substitute sand source for backfill grouting liquid was discussed. Based on actual conditions, the influences of grout performance and grouting parameters on the diffusion of the grouting liquid in the seepage stage were studied. The effectiveness of the muck grout was verified by monitoring values such as surface settlement and segment uplift in the field test. The results showed that silty fine sand can be used as the sand source for preparing grouting liquid that meets the requirements of on-site construction through the addition of a water-reducing agent and by optimizing the ratio. The grouting liquid with the best performance has advantages in terms of 7 d and 28 d strength, bleeding rate, and cementation strength. The stability of this grouting liquid is good, and 44.6% of costs can be saved; the cost-optimized ratio grouting liquid has advantages in 7 d strength and economic benefit, and 74.6% of costs can be saved. However, the stability of this grouting liquid is poor. Under the same grouting time, the pressure generated by the muck grouting liquid and the field grouting liquid on the unit area of the segment is close.