Large-scale Model Experiments Research Articles

Analysis of Factors Influencing Tunnel Block Collapse in Blocky Rock Masses: Insights from Large-Scale Model Experiments and DDA Simulations

Analysis of Factors Influencing Tunnel Block Collapse in Blocky Rock Masses: Insights from Large-Scale Model Experiments and DDA Simulations

Calculating the number of radial cracks around a wellbore fractured by liquid CO2 phase transition blasting technology

Integrating liquid CO2 phase transition blasting (LCPTB) technology with hydraulic fracturing (HF) methods can help reduce wellbore damage, create multiple radial fractures, and establish a complex fracture network. This approach significantly increases the recovery efficiency of low-permeability oil and gas fields. Accurately calculating the number of fractures caused by LCPTB is necessary to predict production enhancement effects and optimize subsequent HF designs. However, few studies are reported on large-scale physical model experiments in terms of a method for calculating the number of fractures. This study analyzed the initiation and propagation of cracks under LCPTB, derived a calculation formula for crack propagation radius under stress waves, and then proposed a new, fast, and accurate method for calculating the number of fractures using the principle of mass conservation. Through ten rock-breaking tests using LCPTB, the study confirmed the effectiveness of the proposed calculation approach and elucidated the variation rule of explosion pressure, rock-breaking scenario, and the impact of varying parameters on number of fractures. The results show that the new calculation method is suitable for fracturing technologies with high pressure rates. Recommendations include enlarging the diameter of the fracturing tube and increasing the liquid CO2 mass in the tube to enhance fracture effectiveness. Moreover, the method can be applied to other fracturing technologies, such as explosive fracturing (EF) within HF formations, indicating its broader applicability and potential impact on optimizing unconventional resource extraction technologies.

Large Scale Experimental Study on Waves and Submerged Horizontal Cylinders

A large-scale physical model experiment was conducted to study the interaction between regular waves and submerged horizontal cylinders, breaking through the bottleneck of a low Reynolds number in a traditional small water tank. The surface pressure distribution and overall force of submerged horizontal cylinders at different submerged depths in waves with different heights and periods under a high Reynolds number were analyzed, and the variation in first- and second-order wave forces with wave height periods was analyzed. Subsequently, the influence of the cylinder on the wave field was analyzed, and the reflection coefficient was obtained through the three-point separation method. According to the analysis of the experimental results, the horizontal and vertical forces acting on the submerged cylinder per linear meter are similar, with the horizontal force slightly greater than the vertical force; at the same time, the submerged cylinder has a certain reflection effect on long-period waves. The summary, analysis, and display of relevant experimental results provide validation support for the current high-precision mathematical model as much as possible.

Deformation characteristics and failure evolution in deep high-stress roadways under creep action

As geotechnical engineering continues to expand into deep underground environments, it is common for creep effects to cause large deformations of roadways and damage to supporting structures. For this purpose, a large-scale model experiment is conducted with a 1300 m deep roadway as the engineering background. Creep-similar materials for prototype rock and construction specifications, as well as designed supporting components and work processes, were developed. Pressure-preserved loading is applied for physical models. The results indicate that the sequence of roadway failure is “floor-heave induced roadway-foot deformation → roadway-foot levered sidewall-bulge → sidewall-bulge driven roof-sink → full-section convergence”. The strain of the roadway changes from compressive to tensile, and it fails when the ultimate tensile strain is reached. The surrounding rock within 0.2 times the width of the roadway is extremely fractured and stripped. Multiple intersecting fissures are visible near the roadway and extend from the surface to the deep interior. The integrity reduction coefficient of the surrounding rock in the original support anchorage zone is greater than 80%, and the rockbolts along with the surrounding rock are deformed toward the center of the roadway. The numerical simulation and field test can verify the authenticity of the model experiments. Finally, the countermeasures of “ floor protection and sidewall control” and “surface-shallow-deep” triple-bearing structures are proposed. The research results can guide the control of creep deformations in deep high-stress roadways.

Experimental investigation on the hydraulic characteristics of water inrush in deep buried filled karst conduit considering the permeability

Water inrush in karst areas is a challenge for the safe construction of deep-buried tunnels due to complicated hydrogeological environments, especially encounters with karst structures that are filled with water and sediments. To study the hydraulic characteristics and disaster evolution of filling materials in complex filled karst conduit during water inrush, large-scale model experiments of seepage and water inrush of filling materials with different permeabilities in karst conduit were conducted according to the engineering geological background of the Qiyueshan tunnel. The whole process of initial seepage and water inrush caused by excavation under the conditions of high ground stress and high confined water pressure is presented, and the spatio-temporal evolution characteristics of pore water pressure inside karst fillings were deeply analyzed. The results show that the pore water pressure in karst fillings generally increases with time while decreasing with the seepage path at the initial seepage stage, and it could be divided into the discontinuous stage, nonlinear stage, and linear stage along the seepage path over seepage time. Additionally, there are undisturbed area, disturbed area, and water inrush of filling materials in karst conduit at the excavation stage. The permeability of karst fillings has an obvious impact on the development process of pore water pressure, as well as the zone and degree of excavation disturbance. The adjacent hydraulic gradient could more accurately reflect the hydraulic characteristics of the karst fillings along the seepage path than the average hydraulic gradient, and make it possible to observe the formation process of seepage channels. The karst fillings with higher permeability has a looser structure and higher porosity, which would form more potential seepage channels at the seepage stage and be more affected by excavation disturbance. Therefore, it is easier to develop into the dominant seepage channels and result in water inrush. Research results may provide reasonable guidance for water inrush prevention and reduce disaster consequences during tunneling in karst areas.

Experimental study on instability mechanism and critical intensity of rainfall of high-steep rock slopes under unsaturated conditions

Two critical factors, namely intense precipitation and intricate excavation, can trigger rock mass disasters in mining operations. In this study, an indoor rainfall system was developed to precisely regulate the flow and intensity of precipitation. A large-scale model experiment was conducted on a self-designed physical simulation experiment platform to investigate the failure and instability of high-steep rock slopes under unsaturated conditions. The real-time reproduction of the progressive failure process in high-steep rock slopes enabled the determination of the critical rainfall intensity and revealed the mechanism underlying slope instability. Experiment results indicated that rainfall may be the primary factor contributing to rock mass instability, while continuous pillar mining exacerbates the extent of rock mass failure. The critical failure stage of high-steep rock slopes occurs at a rainfall intensity of 40 mm/h, whereas a rainfall exceeding 50 mm can induce critical instability and precipitation reaching up to 60 mm will result in slope failure. The improved region growing segmentation method (IRGSM) was subsequently employed for image recognition of rock mass deformation in underground mines. Herein an error comparison with the simple linear iterative cluster (SLIC) superpixel method and the original region growing segmentation method (ORGSM) showed that the average identification error in the X and Y directions by the method was reduced significantly (1.82% and 1.80% in IRGSM; 4.70% and 6.26% in SLIC; 9.45% and 12.40% in ORGSM). Ultimately, the relationship between rainfall intensity and failure probability was analyzed using the Monte Carlo method. Moreover, the stability assessment criteria of rock slope under unsaturated condition were quantitatively and accurately evaluated.

Remediation of large-scale model experiment for heavy metal contaminated clayey soil: An optimized mass transfer process strategy of freeze-thaw and washing

To reduce the limitations of the chemical washing method due to soil texture, the freezing technique has been used to enhance the mass transfer efficiency between the eluent and heavy metal contaminants. With the optimized water supplement and cooling conditions, a large-scale model experiment was conducted. Results show that the optimized method is prone to enhancing the eluent intake of clayey soil, leading to an increase in the amount of soil frost heave, which has a feedback effect by breaking the soil structure and enhancing the eluent intake. The synergistic effect of the two is responsible for the improvement of washing efficiency. In addition, after four freeze-thaw and washing cycles, the total removal rates of the metallic elements Pb and Cd reach 58.73% and 69.04%, respectively, satisfying the soil environmental quality standard. The soil bioavailability is effectively reduced by alternating the eluent with ethylenediaminetetraacetic acid (EDTA) and water, thereby reducing the bioavailability of Pb and Cd by 66.01% and 74.18%, respectively. This remediation strategy for heavy metals in clayey soils utilizes alternate freezing and thawing (natural cold energy) in seasonally frozen regions, which is beneficial for constructing an ecological civilization and protecting the environment.

Experimental Study and Theoretical Analysis of the Effect of Surcharge/Unloading at Both Sides of the Ground Surface on an Existing Shield Tunnel at Different Burial Depths

This paper investigates the impact of surcharge/unloading at both sides of the ground surface on an existing underground shield tunnel at varying burial depths. A large-scale indoor model experiment was conducted to study the vertical convergence deformation, tunnel settlement, and additional surrounding pressure of the tunnel at different burial depths when surcharge/unloading occurred at both sides of the ground surface. The effect of tunnel burial depth, surcharge mass, and uneven surcharge at both sides of the ground surface on the additional surrounding pressure of the existing underground shield tunnel was further investigated by theoretical calculation. The results indicate that under the same conditions, greater tunnel burial depth leads to reduced vertical convergence deformation, tunnel settlement, and additional surrounding pressure. Unloading can partially reduce the vertical convergence deformation and tunnel settlement, but it does not completely counteract the effect of the preceding surcharge. In cases of a symmetrical surcharge at both sides of the ground surface above the tunnel, the additional surrounding pressure of the tunnel is symmetrically distributed, with higher pressures at the arch top and arch bottom of the tunnel and lower pressures at the arch waist. This suggests that the arch top and arch bottom of the tunnel are vulnerable points under surcharge and require special attention. The surcharge above the tunnel has the most pronounced effect on the tunnel, followed by the surcharge at both sides of the ground surface, and, finally, the smallest effect from the bias load.

Conducting Large-scale Model Experiments on Xanthan Gum Treated Clay as an Eco-friendly Approach to Soil Improvement

Recently, waste utilization in soil improvement has become immensely popular regarding the optimization of waste disposal, economy, and environmental protection. Most industrial wastes are environmentally hazardous. In this study, xanthan gum, which is an eco-friendly biopolymer, was utilized in soil improvement. Model experiments were carried out to investigate influences of water content, optimum xanthan gum ratio, blending technique, enhancement thickness and curing duration. Consequently, approximately 4.47 times bearing capacity improvement and 3.5 times settlement reductions were attained. Besides, optimum values of 1.75% for the biopolymer ratio, 80°C for the mixing temperature, 42 days for the curing period and 0.75% for the improvement depth were determined. The findings of microstructural analyses also stood up for the existence of chemical and physical improvements in the soil structure.

Experimental and numerical analysis of a non-dismantling repair method for ancient timber arch lounge bridges

Ancient timber arch lounge bridges are precious cultural heritages in China. The woven arch is the main load-bearing structure of the timber arch lounge bridges, and repairing the woven arch is a very important work in the protection of the ancient timber arch lounge bridges, yet there are few studies on the repair methods. This paper proposes a non-dismantling repair method for the woven arch to meet the repair principle of cultural relics, with minimal repair and minimal interference. This method can be used to replace a small number of the components individually. A strengthened spliced log with a lap joint is used to replace the damaged longitudinal log of the woven arch without dismantling the entire structure. Large-scale model experiments and finite element analyses were performed in this paper to study the effects of the repair method on the woven arch. Deflection and force distribution changes of the woven arch caused by the replacement of the longitudinal logs of the woven arch were studied. The results of finite element analyses are in good agreement with the experimental results. The results show that, under dead load, dismantling a longitudinal log of the woven arch has little interference with the deflection. After dismantling a member of the woven arch, the axial force of the dismantled member will transfer to the adjacent members in the same system. The bearing capacity of the repaired woven arch is comparable to the intact woven arch.

Study and Mechanism Analysis on Dynamic Shrinkage of Bottom Sediments in Salt Cavern Gas Storage

Underground salt cavern gas storage is the best choice for the production peak adjustment and storage of natural gas, and is a basic means to ensure the safe supply of natural gas. However, in the process of these caverns dissolving due to water injection, argillaceous insoluble sediments in the salt layer will fall to the bottom of the cavity and expand, occupying a large amount of the storage capacity and resulting in the reduction of the actual gas storage space. Effectively reducing the volume of sediments at the bottom of the cavity is a potential way to expand the storage capacity of the cavity. In this study, a method to reduce the volume of argillaceous insoluble sediments with particle sizes ranging from 10 mesh to 140 mesh, via a chemical shrinkage agent, has been proposed. Firstly, the inorganic polymer shrinkage agent PAC30 was synthesized, and then a set of dynamic shrinkage evaluation methods was established to evaluate the influence of temperature, particle size, concentration, and other factors on the shrinkage performance. Finally, by means of a scanning electron microscope (SEM), the Zeta potential, and static adsorption experiments, the mechanism of the interaction between PAC30 and cavity-bottom sediments was described and verified in detail. The experimental results show that the optimal concentration of PAC30 for dynamic shrinkage is 20 ppm. The shrinkage performance of PAC30 decreases with an increase in temperature, and the smaller the particle size of the insoluble sediments, the worse the shrinkage performance. According to the adsorption experiment and Zeta potential, PAC30 can be effectively adsorbed on the surface of insoluble sediments, and the SEM images show that, after adding PAC30, the particles are tightly packed, and the volume of insoluble sediments is significantly reduced. In the large-scale model experiment, the expansion rate of PAC30 reached 20%, which proves that the shrinkage agent is a potential method to expand the gas storage volume.

Short-Term Morphological Responses of Adjacent Intertidal Flats to the Construction of Tidal Gates in an Estuarine Tributary

Tidal gates cause adverse effects on the ecological environment through the downstream acceleration of sediment deposition. This deposition process and its quantitative analysis have become a hot topic in marine science. A large-scale physical model experiment of morphological responses to the construction of a tidal gate in an estuarine tributary was performed in this study. The sediment distribution characteristics, morphologic patterns, and further analysis of the adjacent intertidal flats were investigated, triggered by the construction of tidal gates at the mouth of the Nanxi River in Zhejiang, China. The results indicated that the flood and ebb tide velocities change dramatically after the construction of the tributary tidal gates. Large amounts of sediment from the mouth of the estuary could not be entirely carried away from the flood phase to the ebb phase, resulting in downstream deposition in the vicinity of the gates. The ebb tide caused erosion of the tidal flats’ surface in the silted intertidal zone that gradually developed into a tidal channel network. The tidal channel bifurcated in the middle–upper part of the intertidal flats through continuous headward erosion, thus promoting the landward expansions of channels. Applying a set of logistic growth models to the mean sinuosity, Hausdorff dimension, and junction number data indicated that the tidal channel development progressively tended toward a state of morphodynamic equilibrium.

The performance of mechanical characteristics and failure mode for tunnel concrete lining structure in water-rich layer

It's a challenging technical problem at home and abroad that it is inevitable to build tunnels in aquifer with the improvement and development of railway network, particularly under the current stringent environmentally-friendly prerequisite. Therefore, the conventional principle “drainage is dominant and combination of drainage and blockage” should be updated with “blockage is dominant and drainage is limited”. Under this background, the mechanical characteristics for tunnel lining structure in aquifer needs to be studied urgently. A series of model experiments were performed to investigate the load-bearing mechanism of the underwater tunnel lining under water pressure. To investigate the load-bearing characteristics of different types of linings, a fully closed water pressure exerting device for a non-circular section tunnel was invented. A large-scale model experiment (1:30) under combined water and soil pressures was conducted to investigate the mechanical characteristics, deformation, stress distribution, crack development process, and failure mode of the mined-tunnel lining in aquifer. The experiment results indicated that for mined-tunnel lining with large section the key sections for controlling instability of both the drainage lining and the waterproof lining were the bottom of the wall and the inverted arch under the two experiment conditions. One had only water pressure, and the other had a variable water pressure and constant soil pressure. For both types of lining structures, the bottom of the wall and the inverted arch appeared cracks and damaged in turn. Furthermore, based on unified strength theory, it was found that compression-shear failure on the inclined section will occur at the bottom of the wall under the action of water pressure, which was different from the compression bending failure at other parts. In this research, the reasonable ultimate water head of the waterproof lining (thick invert, or large invert) and the drainage lining for the high-speed railway tunnel of Class V surrounding rock with a design speed of 350 km/h was proposed which could provide reference for similar tunnel engineering.

A Large-Scale Model Experiment on the Effect of Sheet Pile Wall on Reducing the Damage of Oil Tank Due to Liquefaction

A Large-Scale Model Experiment on the Effect of Sheet Pile Wall on Reducing the Damage of Oil Tank Due to Liquefaction

Design and verification of the loading system and boundary conditions for wind turbine foundation model experiment

Previous studies show that the wind turbine foundation is subjected to the coupling effect of torque-vertical load-horizontal load-bending moment load (i.e., T-V-H-M). In a large-scale model experiment of wind turbine foundation, the existing methods cannot accurately simulate the complex loads, counterweights, or foundation boundary conditions. In this paper, a novel method for simulating the loads and boundary conditions of wind turbine foundation model experiments was introduced, and a series of related confirmatory research was conducted, showing that the proposed multi-point composite loading system can resolve the problem of increasing shear force caused by the conventional single-point bending moment control loading method. Meanwhile, it can satisfy the load matching requirements of T-V-H-M loads under ordinary laboratory conditions. The regional counterweight system provided a simulation method for the weight of the foundation and overburdens soil under the gravity field, which can accurately restore the distribution of the foundation resistance. The stiffness of ground soil had a significant impact on the force characteristics of the foundation structure. It is concluded that the proposed method can achieve an excellent accuracy at a reasonable computational expense.

Sustainable Implementation of Glass Manufacturing Waste and Geogrids in the Improvement of Fine-Grained Soils

Recently, utilization of wastes has become increasingly important in aspects of sustainability and waste disposal. The aim of this study is to investigate the feasibility of using glass manufacturing waste (GMW) for the first time in the relevant literature, geogrids and GMW-geogrid reinforcement to increase the load bearing capacity of a clayey soil (CS) by large-scale model experiments. Initially, optimum water ratios were determined for different ratios of GMW and CS. Secondly, the optimum mixing ratio of GMW was determined. Next, the optimum soil depth improved with GMW and the optimum number of geogrids were investigated. Consequently, a bearing capacity ratio (BCR) increase of 2.23 times was acquired and the optimum mixture ratio was attained for 25% GMW addition. Improvement depth (Rd) and optimum number of geogrids (N) were obtained as 1.75D (D: diameter of the model foundation) and 3, respectively. The highest degree of improvement was reached for geogrids-GMW combination and a minimum waiting period of 7 days was advised in the sequel of such soil improvement work. Out of the observation of micro-structural analyses results, both physical and chemical interactions were encountered throughout the occurrence period of bearing capacity improvements.

Characteristics of CO2 and Energy-Saving Concrete with Porous Feldspar.

In this study, to reduce the use of cement and sand, porous feldspar with excellent economic efficiency was used as a substitute in the heat storage concrete layer. When porous feldspar and four other silicate minerals were used as substitute materials for sand in cement mortar, the specimen with the porous feldspar exhibited approximately 16–63% higher compressive strength, thereby exhibiting a higher reactivity with cement compared to the other minerals. To compensate for the reduction in strength owing to the decreased cement content, mechanical and chemical activation methods were employed. When the specific surface area of porous feldspar was increased, the unit weight was reduced by approximately 30% and the compressive strength was increased by up to 90%. In addition, the results of the thermal diffusion test confirmed that thermal diffusion increased owing to a reduction in the unit weight; the heat storage characteristics improved owing to the better porosity of feldspar. When chemical activation was performed after reducing the cement content by 5% and replacing the sand with porous feldspar, the compressive strength was found to be approximately twice that of an ordinary cement mortar. In a large-scale model experiment, the heat storage layer containing the porous feldspar exhibited better heat conduction and heat storage characteristics than the heat storage layer composed of ordinary cement mortar. Additionally, energy savings of 57% were observed.

Evaluation of layer coefficient ratios for geogrid-reinforced bases of flexible pavements

The benefit of reinforcement in pavement sections can be quantified in terms of Layer Coefficient Ratio (LCR). In the present study, a series of Large-Scale Model Experiments (LSMEs) were conducted to quantify the LCRs considering unreinforced and geogrid-reinforced base layers overlying soft to stiff subgrades. Based on extensive LSME testing of reinforced base layers, LCRs were found to range from 1.01 to 1.33. The existing design philosophy for flexible pavements is extended to design geogrid-reinforced flexible pavements based on LCR values.

Bayesian Updating of Soil–Water Character Curve Parameters Based on the Monitor Data of a Large-Scale Landslide Model Experiment

It is important to determine the soil–water characteristic curve (SWCC) for analyzing landslide seepage under varying hydrodynamic conditions. However, the SWCC exhibits high uncertainty due to the variability inherent in soil. To this end, a Bayesian updating framework based on the experimental data was developed to investigate the uncertainty of the SWCC parameters in this study. The objectives of this research were to quantify the uncertainty embedded within the SWCC and determine the critical factors affecting an unsaturated soil landslide under hydrodynamic conditions. For this purpose, a large-scale landslide experiment was conducted, and the monitored water content data were collected. Steady-state seepage analysis was carried out using the finite element method (FEM) to simulate the slope behavior during water level change. In the proposed framework, the parameters of the SWCC model were treated as random variables and parameter uncertainties were evaluated using the Bayesian approach based on the Markov chain Monte Carlo (MCMC) method. Observed data from large-scale landslide experiments were used to calculate the posterior information of SWCC parameters. Then, 95% confidence intervals for the model parameters of the SWCC were derived. The results show that the Bayesian updating method is feasible for the monitoring of data of large-scale landslide model experiments. The establishment of an artificial neural network (ANN) surrogate model in the Bayesian updating process can greatly improve the efficiency of Bayesian model updating.

Experimental study on combining heterogeneous phase composite flooding and streamline adjustment to improve oil recovery in heterogeneous reservoirs

The heterogeneity of reservoirs is the key factor restricting the development performance of oilfields. Heterogeneous phase composite flooding (HPCF) and streamline adjustment (SA) are both viable strategies for improving oil recovery of heterogeneous reservoirs. However, both strategies have their own deficiencies, which limits further development. In recent years, a hybrid strategy combining HPCF and SA has attracted considerable interest from oil industry. In this paper, two-dimensional (2D) large-scale physical model experiments were performed to verify whether the hybrid strategy could offer better development performance than the single strategy, and the mechanism of hybrid strategy for improving oil recovery was elucidated. On this basis, the influence of SA angle on improved development performance was investigated. Finally, the affected regions of remaining oil in different strategies were proposed. The experimental results indicate that HPCF can effectively improve sweep efficiency and oil displacement efficiency in the main streamline regions; furthermore, it prolongs the time of incremental oil production. Streamline adjustment can forcibly utilize the remaining oil in the low-permeability regions at non-main streamline where water flooding and HPCF are poorly affected. The hybrid strategy can give full play to the respective strengths of each single strategy. Meanwhile, SA provides a good induction effect on HPCF, which creates an excellent opportunity for the latter to effectively displace the remaining oil in the low-permeability regions at non-main streamline over extended periods. When the SA angle is 90°, the best development performance can be achieved. The affected regions of remaining oil in different strategies were proposed in this paper, which affords significant guidance for effective development of heterogeneous reservoirs.