Geomechanical Model Test Research Articles

Experimental investigation on the failure characteristic and synergistic load-bearing mechanism of multi-layer linings for deep soft rock tunnels

Multi-layer linings have been widely used in deep rheological soft rock tunnels for the excellent performance in preventing large-deformation hazards. Previous studies have focused on the bearing capability of multi-layer lining, however, its failure characteristics and synergistic load-bearing mechanisms under high geo-stress are still unclear. To fill the gap, three-dimensional geomechanical model tests were conducted and synergistic mechanisms were analysed in this study. The model test was divided into normal loading, excavating, and overloading stages. The surrounding rock deformation was monitored by using an improved high-precise extensometer measurement system. Results show that the largest radial deformation appears on the sidewall, followed by the floor and vault during the excavating stage. The relative convergence deformation of sidewalls springing reaches 1.32 mm. The failure characteristics of the multi-layer linings during the overloading stage undergo an evolution of stability, crack initiation, local failure, and collapse, with a safety factor of 1.0–1.6, 1.6–2.0, and 2.0–2.2, respectively. The synergistic load-bearing mechanism analysis results suggest that the early stiffness and late yielding deformation capacity of large deformation support measures play important roles in stability maintenance both in the construction and operation of deep soft rock tunnels. Therefore, the combination of yielding support or a compressible layer with reinforced support is recommended to mitigate the effect of the high geo-stress.

Research and Application of Geomechanical Model Test Technology

Geomechanical model test is one of the commonly used experimental methods in the study of slope stability. It constructs the scale model of slope, simulates the geological environment and load, and carries out the corresponding load experiment to study the stability of slope and its influencing factors. This paper introduces the principles and characteristics of geomechanical model test from the aspects of similar principle, model material selection and key simulation technology.

Research on Rock Support Technology of Railway Tunnels Based on Geomechanical Model Tests

Research on Rock Support Technology of Railway Tunnels Based on Geomechanical Model Tests

Analysis and Experimental Study on the Stability of Large-Span Caverns’ Surrounding Rock Based on the Progressive Collapse Mechanism

The collapse failure of rock surrounding caverns involves a progressive collapse process. Based on the nonlinear Hoek–Brown failure criterion and the upper limit theorem, the whole process curve of the progressive collapse of the surrounding rock of a large-span cavern is outlined in this paper. The progressive collapse process of the surrounding rock of the large-span cavern is experimentally studied using an independently developed visualized large-span-cavern geomechanical model test device with variable angles. The results show that, through theoretical calculation and model tests, the surrounding rock at the top of the large-span cavern undergoes three collapses. Under the condition of rock mass and the shape of the cavern, the larger the span of the cavern, the more times the surrounding rock collapses; with the increase in surrounding rock pressure, the first collapse occurs in the middle part of the arch roof. When the overlying load reaches a certain level, the arch foot becomes the weakest part, and the rock undergoes shear failure along the arch foot, gradually extending upwards, accompanied by multiple collapses, forming a progressive collapse process. The theoretical calculation results of this paper are basically consistent with the scope of the model test, and the research results can provide a basis for the construction and support design of the large-span cavern.

Research on cooperative control method of comprehensive pressure relief and anchor grouting reinforcement in deep mining roadways

To address the surrounding rock control problems in high-stressed deep mining roadways, we used Suncun Coal Mine with maximum mining depth in China as the engineering background to analyze failure laws of surrounding rock of gob-side entry driving. Combined with field tests of anchor grouting parameters, we carried out numerical simulation with multi factors. The evolution of surrounding rock stress and displacement under different pressure relief parameters were clarified. On the basis, we proposed an integrated control method for the comprehensive pressure relief for coal and rock mass and anchor grouting reinforcement in deep mining roadway. We used geomechanical model test to compare gob-side entry driving method and this new method. The results showed that this new method can reduce average stress at the working face by 15.8% and peak stress of roadway shoulder by 12.5%. We applied this method in the field, which reduced roadway deformation by 535 mm.

Geotechnical Model Testing with High-Strength Gypsum Similar Materials: A Case Study on Quartzite-Like Formulations

This paper explores the formulation and optimization of high-strength gypsum-based similar materials for geomechanical model tests, with a specific focus on their application in simulating conditions analogous to quartzite. Employing an orthogonal experimental design, key factors such as quartz sand-to-gypsum ratio, cement-to-gypsum ratio, and barite content were systematically varied. Through a series of indoor experiments, comprehensive assessments of physical and mechanical properties, including density and compressive strength, were conducted for diverse material ratios. The results reveal a broad spectrum of physical and mechanical indicators, aligning with the requisites for model tests across varying similarity ratios. Notably, a high-strength gypsum formulation yielding a uniaxial compressive strength within the precise range of 10~20 MPa was identified, providing valuable insights for researchers engaged in hard rock model tests using similar materials. The study underscores the influential roles of barite content, quartz sand-to-gypsum ratio, and cement-to-gypsum ratio on the density and compressive strength of similar materials. This research contributes essential data for the application of high-strength gypsum in geotechnical model testing, particularly in replicating the mechanical behavior of quartzite.

Damage Process Criterion for the Concrete Dam in Geomechanical Model Test

The geomechanical model test (GMT), a means of intuitively exploring the model’s failure modes and revealing failure mechanisms, is considered an effective approach for studying the structural characteristics of dams under complex geological conditions. However, during the overloading process of the model, the catastrophe trends of monitoring data are unclear, and catastrophe points differ at different monitoring sites. These factors have led to large errors in the judgment of researchers regarding the model’s state and misperception of the structural properties during the damage process. In this study, a comprehensive evaluation method for the model’s state intervals in the damage process is proposed. The criterion employed an interval analysis hierarchy process that considered the differences, consistency, and credibility (CDC‐IAHP) among multiple decision‐makers (DMs), effectively reducing the subjectivity of their judgments. Additionally, this process was combined with cusp catastrophe theory (CCT) to determine whether the model underwent an abrupt change at various overload factors comprehensively. This is the first time that CDC‐IAHP and CCT have been combined as criterion for a comprehensive method on the damage process of concrete dams in GMTs, and was applied to the Wudu gravity dam, indicating its applicability is very good. Compared to the researcher’s judgment, this approach is used to analyze and judge the structural state more accurately and scientifically while reducing subjectivity, which can help to better understand the structural characteristics and bearing capacity of actual engineering projects.

The formation mechanism of dynamic water and mud inrush geohazard triggered by deep-buried tunnel crossing active fault: Insights from the geomechanical model test

Water and mud inrush geohazard is one of the most important geohazards for underground engineering. Understanding the formation mechanism of water and mud inrush is critical for directing the prevention and control of this geohazard. As a result, a large number of methods have provided insight into this topic, such as the geomechanical model test. However, this geohazard triggered by deep-buried tunnel crossing active fault has not yet been explored. Thus, this study develops a geomechanical model test system to simulate the dynamic water and mud inrush caused by Kangding No.2 tunnel crossing Yunongxi active fault. The results imply that seismic loading can result in fluctuating changes in seepage pressure and stress in the tunnel rock mass. Increasing seismic intensity broadens the fluctuation range, together with a dramatic rise in peak seepage pressure. The coupled effect of earthquake loading and high seepage pressure makes the water-resisting rock mass extremely vulnerable to fracturing, increasing the probability of water and mud inrush. High seismic intensity leads to rock fracture propagation, ulteriorly giving rise to stress releasing, eventually provoking the fracturing of rock mass. Precursor of water and mud inrush can be observed before the geohazard occurs, reflected by the gradual rise of seepage pressure and intermittent fluctuation of stress. Following the increasing earthquake intensity, peak acceleration occurs in a random position of water-resisting rock mass, but mostly appears at the tunnel contour of surrounding rock. The free face of the tunnel exerts an amplifying effect on seismic acceleration. Seismicity affects the formation of water and mud inrush from active fault, which ulteriorly determines the minimum safety thickness of water-resisting rock mass. Monitoring the seepage pressure and stress in water-resisting rock mass is effective for the early warning of inrush hazard.

Geomechanical Model Test on the Zonal Disintegration of Deep Tunnel in Jinping II Hydropower Station

Zonal disintegration is commonly encountered during the construction of tunnels at large depth. To study the formation and evolution mechanism of zonal disintegration in deep tunnels, a geo-mechanical model test is conducted under three-dimensional condition. The results reveal that: 1) with the proceeding of tunnel excavation, the displacements and the stresses around the tunnel present oscillating variation with alternating peak and trough. 2) Four annular rupture zones can be found around the tunnel, where the distance between the outermost rupture zone and the tunnel periphery is approximately 9.6 m. 3) The rupture zone first forms on the sidewalls of the tunnel, and then gradually develops to the interior of the rock mass until a complete ring-shaped rupture zone is formed. 4) The evolution of zonal disintegration is affected by the shape of cross section. The reproduction of zonal disintegration in laboratory can effectively reveal the formation mechanism and develop the control measures. The results obtained will provide important scientific basis for the safety construction of deep underground engineering.

Geo-mechanical model test on excavation and support of deep tunnel crossing a fault under hydro-mechanical coupled condition

Geo-mechanical model test on excavation and support of deep tunnel crossing a fault under hydro-mechanical coupled condition

Negative Poisson’s ratio cable compensation support for 32 m super-large-span highway tunnel: A case study

Although super-large-span tunnels ensure convenient transportation, they face many support challenges. The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of super-large-span tunnels. Based on the geological conditions of a super-large-span tunnel (span = 32.17 m) at the bifurcation section of the Shenzhen interchange, this study determined support parameters via theoretical calculation, numerical simulation, and engineering analogy. The support effects of negative Poisson’s ratio (NPR) anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied. Further, based on FLAC3D simulations, the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions, and the mechanism of a long-short combination, high-prestress compensation NPR anchor cable support was revealed. On the basis of numerical simulations, to our knowledge, the three-dimensional (3D) geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time, revealing the stress evolution law of super-large-span tunnels, deformation and failure characteristics of the surrounding rock, and the changing trend of the anchor cable’s axial force, and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables. This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.

A Geomechanical Model Test on the Construction Stability and Overload Failure Process of an X-Type Cross Cavern Group

The geological environment of the surrounding rock in deep underground engineering will become more and more complex, along with the excavation depth continuously increasing. Under these conditions of high temperatures, high seepage, high geostress, and strong excavation disturbance, the surrounding rock during underground engineering can experience obvious nonlinear deformation failure. In order to guarantee the construction, excavation, and operational safety of deep underground engineering, we have to comprehensively study the failure characteristics and deformation characteristics of the surrounding rocks of the cavern. To reveal the interaction between structures and the characteristics of overloading-induced damage and safety factor, a geomechanical model test of an X-type cross cavern group was carried out during the excavation process and overloading process. The engineering background is the URL of HLW for the geological disposal in Beishan. This is the first time that this type of geomechanical model test is being carried out. The law of displacement and stress change during the process of excavation and the law of deformation and the failure of surrounding rock in the process of overload are obtained. The test results show that the stress and displacement changes at the intersection of the caverns are most significant after excavation. The excavation’s impact range is approximately 1.5 to 2 times the tunnel diameter. Under these test conditions, the safety coefficient of the crack initiation is 2.1, the safety coefficient of the local destruction is 2.5, and the safety coefficient of the general demolition is 2.9. These test results provide technical support for the design and construction of an URL for the deep buried geological disposal of HLW and have important practical significance.

Research on the Experimental System of Reinforcing the Base of Shallow Buried and Wet Collapsible Loess Tunnels

Due to the complexity of the surrounding rock structure and the geological environment of tunnel excavations, traditional analytical methods are insufficient in effectively dealing with the complex nonlinear deformation problems arising from tunnel excavation. In contrast, geomechanical model tests can comprehensively simulate the excavation construction process of tunnels and the mode and time effects of loads, providing a more realistic reflection of the complete process of engineering stress and deformation. Therefore, this study conducted a model test on reinforcing the loess tunnel base, building upon the first tunnel of the Lanqing Expressway located on the north bank of the Yellow River in Lanzhou City. The study utilized similarity theory to explore the theoretical design of the model and established a specialized model test platform to design the experiments with the goal of obtaining more scientific and effective experimental schemes to ensure the safety of soil reinforcement in tunnel bases during construction. This research will contribute to improving the safety, reliability, and economy of loess tunnel base reinforcement projects, and has a certain reference value for research in this field.

Experimental study on similar materials for tunnel lining concrete in geomechanical model tests

In geomechanical model tests, a reasonable proportioning of similar materials is one of the keys to ensuring that the physical and mechanical properties of the model match those of the prototype. Using gypsum, white cement, barite powder, quartz sand, and water as raw materials, a similar material of tunnel lining concrete was developed by orthogonal design. The density, compressive strength, elastic modulus, and tensile strength of the similar material were measured, which were evaluated using range analysis. Meanwhile, the mechanical parameter relationship was studied between the similar material specimens with different sizes. The results show that the similar material has a large range of physical and mechanical parameters, and can be used in the model test with a large unit weight; its ratio of compressive strength to tensile strength is 8.31–16.12, which conforms to the mechanical properties of concrete. The aggregates/cementing materials ratio has the largest impact on the material density, while the water/cementing materials ratio has the greatest influence on the strength and elastic modulus of the material. There is a good fitting relationship between the mechanical parameters of cylinder specimens and the mechanical parameters of cube and prism specimens, so cylinder specimens can be prepared for mix proportioning tests during trial preparation of the similar material. The physical and mechanical performance of grade-C25 concrete and grade-C40 concrete can be well simulated by the developed similar material. The research can provide a reference for the selection of similar materials for lining concrete in similar model tests.

Physical Model Test on the Deformation and Fracturing Process of Underground Research Laboratory during Excavation and Overloading Test

Understanding the excavation-induced deformation and failure behaviors of the URL (underground research laboratory) for the geological disposal of HLW (high-level radioactive waste) before its construction is essential due to its high safety requirements. To reveal the interaction between structures, the effect of supporting and the characteristics of the overloading-induced damage and safety factor, we carried out a physical model test on the deep underground chamber groups consisting of one main roadway and two parking lots (one is supported, the other is not supported), and the engineering background is the URL of HLW for the geological disposal in Beishan. This type of geomechanical model test is still the first to be carried out so far. The test results confirm that the chamber group is generally stable during the excavation process. After the excavation, the displacement of the intersection is 7–33% larger than that of the non-intersection. The displacement of the supported chamber is reduced by 14–22% compared with that without support. The tension of the bolt at the vault top is greater than that at the waist of the cave. Without support, the safety coefficient of crack initiation is 1.7; the safety coefficient of local destruction is 2.1; and the safety coefficient of general demolition is 2.3. In contrast, the safety coefficient of crack initiation is 1.9; the safety coefficient of local destruction is 2.2; and the safety coefficient of general demolition is 2.4 when the rock mass is supported. The research results provide an important basis for optimizing design schemes and evaluating the safety of the construction process for URL.

Sensitivity Analysis of Mechanical Parameters of Collapse Roof of Carbonate Rock Deep Buried Oilfield

Carbonate rock oilfields account for two-thirds of proven marine carbonate oilfield reserves, which are the primary way to increase future oil and gas energy reserves. Cave collapses occur during the process of oil reservoir development, seriously affecting oil production. In order to reveal the collapse failure mechanism of carbonate karst caves and predict whether the fracture cave type oil reservoir will collapse before drilling, a binary depth reduction method for determining the critical collapse depth of karst caves is proposed based on the Tahe fracture cave type oil reservoir. The sensitivity of karst cave collapses to multiple factors is analyzed, and a prediction formula for the critical collapse depth of karst caves with changes in the deformation modulus, the internal friction angle, and the cohesion is established through multiple regression analysis. By calculating and analyzing the numerical values of a large number of operating conditions under different mechanical parameters, the failure process, failure mode, and the change law of collapse depth during the Tahe oilfield destruction process were obtained. We used the established formula for predicting the collapse depth of karst caves to predict and analyze the actual distribution of karst caves in the Tahe oilfield. The calculation and analysis results showed that in the karst cave failure mode characterized by vertical shear failure, the cohesive force is the most sensitive factor affecting cave collapse, followed by the internal friction angle. The deformation modulus is hardly sensitive to the influence of the karst collapse. Through the geomechanical model test, the result verified the accuracy and reliability of the calculation results. The research results will provide necessary theoretical support for the large-scale safe extraction of deep petroleum resources, increase oil production in China, and have important theoretical significance and engineering application value.

Physical model test of tunnel complex surrounding rock progressive failure based on strength-reduction similar materials

Similar materials are key to geomechanical model tests of tunnels. The strength-reduction method is commonly used in geotechnical engineering. In this study, a similar material for quantitative strength-reduction by temperature change was developed to simulate the strength-reduction method. Similar materials include paraffin wax, quartz sand, and barite powder. The parameters of similar materials at different temperatures were tested. The strength parameters of similar materials were quantitatively controlled through temperature changes to reduce their strength. Physical model tests were conducted for the progressive failure of a tunnel based on similar materials with a temperature control system. Physical model tests were carried out with the Hongyan Village tunnel complex as the engineering background; the research results revealed the deformation, force, and damage characteristics of the tunnel complex surrounding rock. The results were compared with calculated results using an FEM-based strength- reduction method. Physical model tests can simulate the process and characteristics of progressive failure of the tunnel surrounding rock and provide a reference for assessment of the factor of safety (FoS) and ultimate bearing capacity.

Experimental investigation of face instability for tunnels in sandy cobble strata

In order to investigate the influence of face instability for tunnels with different burial depths in sandy cobble strata on earth pressure and the instability region, geomechanical model tests and numerical simulations were performed. The continuous excavation method was adopted to reduce the pressure of the soil bin and restore the real engineering situation. Earth pressure in three directions of the observation section in front of the tunnel face was monitored during the tunneling of the shield. Evolutions of the lateral stress ratios at different stages were also investigated. The instability area of the shield tunnel face in sandy cobble strata with different burial depth ratios during the instability stage was obtained based on the change ratio of earth pressure and compared with existing researches. The earth pressure began to change when the excavation was one shield diameter away from the observation section, and when the excavation reached the observation section, the earth pressure decreased significantly. The burial depth of shield tunnel in the sandy cobble strata has a significant impact on the evolution of soil arch and the size of the failure area. The numerical simulation of the continuum medium cannot reflect the stress redistribution characteristics of the granular body like sandy cobble strata, and the failure area or stress disturbance area obtained by the model test is larger than the numerical simulation result. Existing methods have deviations in analyzing the failure area of shield tunnel face in sandy cobble strata. It provides not only guidance for shield tunnel excavation engineering in sandy cobble strata, but also a reference for the theoretical research on failure areas.

Experimental study of face stability for shield tunnels in sandy cobble strata of different densities

This paper aims to study the influence of relative density on the working face stability of shield tunnel in sandy cobble stratum. A series of geomechanical model tests were conducted for shield tunnels excavating through loose sample (LS), medium dense sample (MS) and dense sample (DS), respectively. Relative densities of LS, MS and DS are 0.35, 0.55, and 0.75. The method of continuous rotation of spiral excavators while shield excavators stop tunneling is adopted to simulate the instability of tunnel face. Experimental results effectively reveal the variation characteristic of vertical and horizontal earth pressure and lateral pressure coefficient of shield tunneling. The evolution of the failure zone and soil arch height of strata with different densities was explored. The failure area and collapse range obtained from the model test were compared with the existing method. The effect of relative density on the horizontal earth pressure in the instability stage of the tunnel face in the sandy cobble strata is greater than that of the vertical earth pressure. In addition, increasing the relative density can effectively increase the lateral pressure coefficient as well as the stability of the tunnel face. The existing methods have deviations in analyzing the instability area of the tunnel face in the sandy cobble strata with different relative densities. The research in this paper provides a reference for the construction and theoretical analysis of sandy cobble strata shield tunnel engineering.

Experimental study on mechanical properties and failure behaviours of new materials for modeling rock bridges

Rock bridges control the stability of rock slopes with intermittent joints. To better understand the evolution of water-induced damage in rock bridges, we developed new, water-sensitive similar materials and investigated their physical, mechanical, and hydraulic properties. The reasonable proportions of the material components required to simulate a rock bridge were systematically determined based on deformation failure modes, shear creep characteristics, deterioration degree, and the brittleness characteristics after water-rock interaction. Sensitivity analysis and contribution rates were used to characterize the effects of different influencing factors on the mechanical properties of similar materials. We found that one similar material specimen, SM-24, exhibited the analogous characteristics of natural rock bridge in shear creep behavior, crack propagation, and ruptured surfaces. Such similar material for modeling rock bridges has the following mechanical characteristics: reproducing the volume-expansion point, showing high deterioration degree and specific brittle failure characteristics after water-rock interaction, and reproducing the identifiable precursor of accelerated creep and stepped fracture morphology subjected to shear creep loading. The bone-binder ratio dominated mechanical properties of similar materials, while physical and hydraulic properties depended mainly on the bentonite content. These findings provide guidelines for reliably producing similar materials that meet the requirements of different geomechanical model tests in solving geotechnical engineering problems considering the water-rock interactions.