Excavation Project Research Articles

Deformation of Existing Shield Tunnel Adjacent to Deep Excavations: Simulation and Monitoring Analysis

Deep excavations near subway tunnels can induce deformation, necessitating a comprehensive investigation into causal factors and mitigation strategies. Field measurements were conducted to assess both vertical and horizontal displacements of existing tunnels near a deep excavation in Shenzhen. Utilizing a validated three-dimensional finite element model that considers structure−strata interactions, this study analyzes tunnel displacements, ground movements, diaphragm wall impacts and the sensitivity of enclosure structure parameters. The results indicate that tunnel deformation correlates with enclosure structure deformation, particularly near the center of the pit. Moreover, shallow soil excavation significantly affects the vertical displacement of shallow-buried tunnels. However, the design parameters of the existing enclosure structures inadequately limit tunnel displacement. Therefore, it is crucial to intensify vertical displacement monitoring in shallow tunnels during early excavation stages and to enhance horizontal displacement monitoring during later phases. Implementing measures such as optimizing central support design or retaining soil at the pit bottom helps control maximum horizontal displacement. While support stiffness plays a greater role than retaining wall thickness, its impact on deep excavation projects is limited.

Research and engineering practice of 70-m long-distanceaxial-force servo steel support technology

For deep excavation projects in areas with soft soil and a sensitive surrounding environment, an axial force servo steel support is usually adopted to control the deformation of retaining structures; however, the traditional axial force servo steel support can only be applied to deep excavations with a width of approximately 20 m owing to its technological limitations. In this study, considering the deep excavation project of Shanghai Xuhui Riverside Area A as an example, relevant technical research on a 70-m long-distance axial force servo steel support was conducted and the effect of this steel support in engineering practice was analyzed. Through the successful application of the project, the engineering safety reliability and deformation control effectiveness of the 70-m long-distance axial force servo steel support were verified, which can provide a reference for the design of similar projects.

Effect of flexural deformation on the bearing capacity of assembled H-shaped steel strut: A case study

Abnormal flexural deformation was found in one assembled H-shaped steel strut (AHSS) of an excavation project. In order to assess the effect of flexural deformation on its bearing capacity, a field axial loading test was carried out before the dismantling of the AHSS. It was found that, due to the weak region around the loading component, the horizontal and vertical displacements were larger for the monitoring points closer to the loading component. The horizontal displacements of points H3 ~ H7 all exceeded the required limit value, and the maximum descent of each monitoring point was smaller than the required limit value. Steel columns showed negligible contribution to the restrict of the horizontal displacement but relatively good vertical support of the AHSS. As compared to the condition considering normal deformation, the safety redundancies of the AHSS were all smaller when considering the abnormal deformations. The mechanism of the flexural deformation was discussed, and suggestions for avoiding such abnormal flexural deformation were given.

Emergency Strategies for Gushing Water of Borehole and Numerical Simulation on Circular Diaphragm Wall Excavation with Ring-Beams

This study explores the underground structure and soil retention capabilities of a large-scale circular diaphragm wall (93.5 m in diameter) utilized as a soil retention strategy in deep excavation projects. The symmetrical design of the wall facilitates the use of an unsupported construction method, effectively resisting soil and water pressures. Using PLAXIS 3D 2017 software, this study simulates wall deformation and ground settlement, employing three different soil models to assess behavior under standard and emergency water gushing scenarios. The results show that the hardening soil (HS) model most accurately reflects the actual deformations and settlements. This study also finds that adjusting Young’s modulus for clay significantly impacts the accuracy of soil behavior predictions, while changes in the properties of sand have minimal effects. This research highlights the challenges posed by water gushing and suggests the need for model improvements to capture better the dynamic interactions between soil and water pressure, which could lead to wall tilting. Overall, this study offers innovative and practical value, providing crucial insights for designing and mitigating strategies in large-scale circular deep excavation projects, especially in regions such as Taiwan, where such constructions are rare and face unique challenges.

Experimental research and application of drilling and blasting with directional damage-reduction shaped charge

In this research, a directional reduction charging structure was proposed to solve the problems caused by drilling and blasting method such as serious damage to surrounding rocks, working face low contour flatness and serious over-under break of root base c. Drilling and blasting tests, numerical calculations and field applications were designed and performed for the verification of the blasting advantages of charge structure. Test results showed that the peak positive strain along the protection direction of directional protection shaped charge was significantly smaller than that of ordinary charge, where PVC material presented the strongest effect such that the peak positive strain of specimen 1 at measuring point 4 (protection direction) was only 0.27 times that at measuring point 9 (non-protected direction). Numerical simulations indicated shaped jet formation, damage-reduction and charge penetration process and obtained the force law of cement target plate. Experimental results revealed that application of charge in tunnel controlled blasting achieved a clear controlling effect on contour line excavation. Compared with ordinary smooth blasting method, all technical indicators of the developed method were improved such that half hole mark rate was increased by about 33% and the amount of over-under break was decreased by about two times. Research results are of certain significance for the stability of surrounding reserved rocks and formation of roadway in blasting engineering and the developed method was found to be applicable to mining, shaft excavation and other projects.

Experimental Research on the Floating Amount of Shield Tunnel Based on the Innovative Cumulative Floating Amount Calculation Method

The study of shield tunnel segment flotation is crucial for controlling the precision of underground excavation projects. Based on Winkler’s beam foundation theory, the load structure method, and the equivalent continuous beam model, and by considering the mechanical and spatial conditions that cause segment flotation, a novel theoretical calculation method for cumulative flotation is proposed using a simplified equivalent stiffness model of the tunnel. Additionally, a new concept of “equivalent flotation force” is introduced. The rationality and applicability of this theoretical calculation method are verified by comparing it with on-site construction data from the Yuanjiang River Crossing Tunnel Project in Changde, Hunan Province, China. The experimental results demonstrate that the theoretical calculation closely approximates the surface deformation monitoring data of the tunnel alignment in the eastern section of the project, and their deformation patterns are similar. Near the starting shaft, there is significant settlement influenced by stratum loss due to smaller tunnel flotation, with greater settlement occurring in the upper part. However, at approximately 45 m into both sections, they enter a deformation stability zone showing significant correlation in longitudinal deformation. Through comparison and verification of on-site experiments and theoretical model analysis, we preliminarily elucidate the feasibility of this innovative cumulative flotation theoretical calculation method which provides an important theoretical basis for assessing segment flotation issues in subsequent tunnel shield construction evaluations.

The Excavation of the Remains of Soldiers Killed in the Korean War: Implications and International Cooperation

The main purpose of this article is to explore the significance of the objectives by focusing on activity theory, as well as the legal and institutional establishment of the Ministry of National Defense (MND) Agency for KIA Recovery & Identification (MAKRI), the subject of the Korean War remains excavation project, and the implications of expanding the excavation of remains in the DMZ and the repatriation of the remains of US and UN soldiers on the 70th anniversary of the Armistice Agreement. The excavation project, which began in 2000, aimed to build public trust by realizing the noble will of national unlimited responsibility that “the state is responsible for those sacrificed for the country forever.” Thus, it has allowed social integration beyond ideological and generational conflicts. It expanded the issue of excavating remains from South Korea to Arrowhead Hill and White Horse Hill in the DMZ area under the September 19 Inter‐Korean Military Agreement in 2018. Also, the ROK–US MOU was signed in 2000 in terms of international cooperation in the excavation of remains and carries out joint identification and repatriation of remains. The repatriation of the remains of Chinese troops and the remains of UN combatant countries has important implications for strengthening military diplomacy in legal and humanitarian aspects.

Ground settlement and estimation of maximum settlement value in adjacent foundation pit excavation

The excavation of adjacent pits following the initial foundation pit excavation can significantly influence ground settlement. Using a foundation pit excavation project in Changzhou as a prototype, this study employed the numerical simulation method in conjunction with the HSS model to analyze the settlement deformation characteristics of the original excavation and compare them with the recorded monitoring values. In this study, the analysis focused on the ground settlement between two pits by varying the spacing between them at different excavation depths. The findings revealed that the ground settlement does not exhibit a significant increase when the new pit is excavated at a shallow depth. However, it rapidly increases when the excavation depth of the new pit surpasses that of the existing pit. Furthermore, an increase in the distance between the two pits causes the maximum settlement position to shift towards the edge of the new pit. The maximum ground settlement is found to have a linear relationship with both the maximum horizontal displacement of the two pits and the spacing between them.

Damage Evolution Characteristics and Constitutive Model for Coal and Rock under Asymmetric Loading.

Tunnels and shaft mining roadways are often subjected to varying degrees of asymmetric loading due to terrain relief or project excavation. In order to analyze the influence of the asymmetric degree of loading on the mechanical properties and damage rupture law of coal rock, uniaxial compression tests of coal rock under four asymmetric loading modes were carried out, the influence of the asymmetric coefficients of loading on macro- and micromechanical properties of coal and rock was analyzed, and a statistical damage constitutive model of coal and rock was established to reflect the asymmetric loading degree. The results of the study show that the peak stress of the coal rock decreases gradually with the increase in the asymmetric coefficient of loading, and the two are linear functions of each other. The distribution of the acoustic emission ringing count peak value is concentrated under uniform loading, while the acoustic emission ringing count rate presents a multipeak phenomenon under asymmetric loading, and the peak value points are scattered. In the case of asymmetric loading, the stress concentration on the edge of the upper loading plate leads to shear failure, and the microscopic cracks are concentrated near the interface between the loading zone and the nonloading zone. According to the established damage constitutive model, when the damage degree is the same, the larger the asymmetric coefficient, the smaller the strain value, which indicates that the asymmetric loading promotes the damage of coal and rock.

Transfer component analysis-driven domain adaptation approach for estimating the life of tunnel boring machine disc cutters

Estimating the life of disc cutters in tunnel boring machines is crucial for tunnel excavation efficiency. Accordingly, generating accurate predictions of the state of disc cutters can prevent unexpected downtimes while optimizing cutting performance. The literature presents investigations of the application of machine learning (ML) for estimating the disc cutter life. Nevertheless, diverse excavation conditions and data scarcity have stimulated research on transfer learning (TL) frameworks that tailor models for different domains, that is, domain adaptation (DA), by generating a common subspace in which the discrepancies among them are minimized. This study presents an end-to-end framework to estimate the disc cutter life through transfer component analysis, a DA-based method for projecting different domains by considering excavation project datasets in a common space; then, different ML models are trained, including linear, probabilistic, and neural methods. The results revealed that the Gaussian process regression model was superior to other methods, with R2 = 0.99. In conclusion, TL is a valuable tool for estimating disc cutter life across different domains, enabling accurate predictions and leveraging knowledge to mitigate data scarcity challenges. In addition, an explainable AI analysis is conducted to quantify and identify relevant features impacting negatively on the disc cutter life, evidencing great contribution from the cutter rotation speed, quartz content, screw rate and specific energy.

Uncoupled thermo-hydro-mechanical modeling of a pykrete diaphragm wall for an alternative artificial ground freezing application

El Harrach Center metro station is an actual project constructed with conventional diaphragm walls in Algiers. This article primarily consists of a parametric study that makes use of the station's geometry for comparative analysis. In this way, three gaps are investigated using an alternative artificial ground freezing (AGF) application. The impact of thermal conductivity, specific heat capacity, and thermal expansion on the diaphragm wall’s stability were examined; an innovative pykrete wall was investigated; and a new procedure was developed after modeling 216 cases of diaphragm walls with uncoupled thermo-hydro-mechanical modeling via the Plaxis program. In terms of total displacement, ground settlement, horizontal displacement, and excavation uplift, the diaphragm walls were different with and without thermal modeling by 96.20, 100.50, 4.20, and 2.50 mm, respectively. The effectiveness and stability of the innovative pykrete wall have been demonstrated to accurately represent on-site behaviour due to its perfect comportment against internal forces compared to other types of walls. The new procedure was developed regarding the optimum case that facilitates understanding the factors affecting the AGF method (distance between pipes, pipe diameter, freezing temperature, and freezing duration) according to its importance, cost, and the novel potential of thermal modeling for deep excavation projects.

Stability analysis of civil air defense tunnel under blasting vibration

Based on a large section drilling and blasting excavation project, the dynamic response characteristics of civil air defense tunnels are analyzed by combining field monitoring and numerical simulation. The dynamic response features include particle vibration velocity, main frequency, displacement, and stress, and the stability criterion of the tunnel is analyzed. A safety criterion model based on the ultimate tensile strength of materials is established. The results show that the frequency of the X, Y, and Z directions is mainly distributed in 90-140 Hz. The effective stress increases first and then decreases along the axis of the roadway. The stress near the explosion source is large and the relative reduction is also large. By fitting the relationship between blasting vibration velocity and maximum principal stress, the safe vibration velocity criterion based on tensile strength is obtained, and the safe threshold of vibration velocity is 19.62 cm/s. It can be assumed that blasting does not affect the structure.

Adaptive mutation sparrow search algorithm-Elman-AdaBoost model for predicting the deformation of subway tunnels

A novel coupled model integrating Elman-AdaBoost with adaptive mutation sparrow search algorithm (AM-SSA), called AMSSA-Elman-AdaBoost, is proposed for predicting the existing metro tunnel deformation induced by adjacent deep excavations in soft ground. The novelty is that the modified SSA proposes adaptive adjustment strategy to create a balance between the capacity of exploitation and exploration. In AM-SSA, firstly, the population is initialized by cat mapping chaotic sequences to improve the ergodicity and randomness of the individual sparrow, enhancing the global search ability. Then the individuals are adjusted by Tent chaotic disturbance and Cauchy mutation to avoid the population being too concentrated or scattered, expanding the local search ability. Finally, the adaptive producer-scrounger number adjustment formula is introduced to balance the ability to seek the global and local optimal. In addition, it leads to the improved algorithm achieving a better accuracy level and convergence speed compared with the original SSA. To demonstrate the effectiveness and reliability of AM-SSA, 23 classical benchmark functions and 25 IEEE Congress on Evolutionary Computation benchmark test functions (CEC2005), are employed as the numerical examples and investigated in comparison with some well-known optimization algorithms. The statistical results indicate the promising performance of AM-SSA in a variety of optimization with constrained and unknown search spaces. By utilizing the AdaBoost algorithm, multiple sets of weak AMSSA-Elman predictor functions are restructured into one strong predictor by successive iterations for the tunnel deformation prediction output. Additionally, the on-site monitoring data acquired from a deep excavation project in Ningbo, China, were selected as the training and testing sample. Meanwhile, the predictive outcomes are compared with those of other different optimization and machine learning techniques. In the end, the obtained results in this real-world geotechnical engineering field reveal the feasibility of the proposed hybrid algorithm model, illustrating its power and superiority in terms of computational efficiency, accuracy, stability, and robustness. More critically, by observing data in real time on daily basis, the structural safety associated with metro tunnels could be supervised, which enables decision-makers to take concrete control and protection measures.

Rock-mass heterogeneous rheological properties caused the formation of deep tension fractures

Tension failure is a unique phenomenon in solid Earth that occurs on scales ranging from large plate rift valleys to small laboratory rocks. On a slope scale, deep unloading tension fractures are distinct from conventional unloading fractures and are a unique geological phenomenon in valleys with high in-situ stress. To accurately reproduce the development and evolution of deep unloading tension fractures and to support major excavation projects, a series of works including geological investigation, laboratory tests, intrinsic model establishment, and numerical simulation were carried out in this study. The unloading rheological tests, accounting for time-dependent effects, uncover the heterogeneity in the rheological attributes of rock-mass strength parameters during valley downcutting. This heterogeneity manifests as a transition in rock-mass strength parameters that cohesion weakening-friction strengthening (CWFS). Drawing on the results of laboratory tests, a novel viscoelastic-plastic model, termed the WSR model, was proposed. This model takes into account both CWFS and rheological considerations. It has been applied to simulate deep unloading tension fractures in the Jinping I hydropower station (JP-I) and compared with conventional models. The results show that WSR model accurately reproduced the development and evolution of deep unloading tension fractures and the heterogeneity of rock-mass deformation during age evolution leads to the formation of deep unloading tension fractures. In this study, the rock-mass heterogeneous rheological properties were summarized as the heterogeneity of the rock-mass strength parameters during age deterioration and the heterogeneity of rock-mass deformation during age evolution; the WSR model was proposed to characterize the heterogeneous rheological property of rock-mass strength parameters and to reproduce the development and evolution of deep unloading tension fractures in the JP-I. This novel contribution to deep unloading tension fractures emphasizes that the rock-mass heterogeneous rheological properties lead to the formation of deep unloading tension fractures.

Numerical study of creep in soil anchor walls - a case study

ABSTRACT One of the fundamental unknowns in geotechnical engineering, particularly in the design and analysis of retaining walls, is creep. Traditional design approaches for anchored walls often specify a certain prestressing force in the anchors while allowing minimal wall displacement. Unfortunately, the long-term effects of creep are frequently overlooked. Over time, creep leads to increasing displacement in anchored walls, changing the loads acting on stabilizing elements and diminishing the factor of safety for excavation stability. While past research has predominantly focused on short-term behaviour in anchored and nailed walls, only limited attention has been devoted to their long-term behaviour. This study addresses the existing gap by collecting data related to the long-term behaviour of anchored walls in an excavation project. Utilizing two-dimensional finite element numerical modelling, using plane-strain analyses, the study predicts the behaviour of these walls both at the end of the excavation and five years after its completion. Long-term behaviour modelling employs a history matching approach to determine creep variables. Subsequently, the study investigates horizontal wall displacements and changes in loads within the anchors over a five-year period. Through a comparison of modelling results with field measurements, the study demonstrates the model validation in forecasting horizontal displacements at various locations and changes in loads on the anchors over time. Furthermore, the proposed method for long-term deformation calculations of excavation walls enables the anticipation of when horizontal wall displacements may surpass allowable limits. This research concludes with an examination of the evolving trends in anchor loads over time, substantiated by a combination of measurements and numerical modelling.

Multi-Stage and Multi-Parameter Influence Analysis of Deep Foundation Pit Excavation on Surrounding Environment

As urbanization accelerates, deep excavation projects have become increasingly vital in the construction of high-rise buildings and underground facilities. However, the potential risks to the surrounding environment and the inherent complexities involved necessitate thorough research to ensure the safety of those engineering projects with deep foundation pit excavation and to minimize their impact on adjacent structures. This study introduces a multi-stage and multi-parameter numerical simulation method to scrutinize the construction process of deep foundation pits. This approach not only investigates the influence of excavation activities on nearby buildings and roads but also enhances the fidelity of simulation models by establishing a three-dimensional finite element model integrated with on-site investigated geological information. Therefore, the proposed method can provide a more holistic and accurate analysis of the overall impacts of the pit excavation process. To examine the feasibility and effectiveness of the proposed method, this study adopts the multi-stage and multi-parameter influence analysis approach for a real practical engineering case to explore the impact of excavation on the foundation pit support structure, nearby buildings, and surrounding roads. The foundation pit support’s maximum displacement was 8.64 mm, well under the 25 mm standard limit. Anchor rod forces were about 10% below the standard limit. Building and road settlements were also minimal, at 10.33 mm and 16.44 mm, respectively, far below their respective limits of 200 mm and 300 mm. This study not only validates the feasibility of design and construction stability of deep foundation pits but also contributes theoretical and practical insights, serving as a valuable reference for future engineering projects of a similar scope.

Influence of Deep Foundation Pit Excavation on Adjacent Pipelines: A Case Study in Nanjing, China

To investigate the pipeline deformation pattern caused by the excavation of deep foundation pits in composite soil–rock strata, a comprehensive study integrating on-site monitoring and numerical simulation was conducted. This study centered on a deep foundation excavation project in the soft soil in Nanjing’s floodplain region. The analyses of pipeline settlement and deformation were performed based on field-measured data. This study investigated the impact of excavation on the mechanical properties of the surrounding soil that resulted in the progressive deformation of adjacent pipelines. Furthermore, numerical simulations were conducted using Plaxis 3D CONNECT Edition v22 finite element analysis software. This study elucidated the influence of factors such as pipeline–pit distance and burial depth on pipeline deformation, conducting a quantitative analysis of their effects. The results indicated that deformation primarily occurs unevenly near pit corners and is less pronounced in soil–rock strata than in single-type soil layers. This study established correlations between pipeline displacements and various factors, offering valuable insights for future excavation projects conducted under similar conditions.

Subsurface multi-physical characterization of mountain excavation and city construction in loess plateau with a fiber-optic sensing system

Mountain excavation and city construction (MECC) projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land. Understanding the subsurface evolution characteristics of the artificial land is essential, yet challenging. Here, we use an improved fiber-optic monitoring system for its subsurface multi-physical characterization. The system enables us to gather spatiotemporal distribution of various parameters, including strata deformation, temperature, and moisture. Yan'an New District was selected as a case study to conduct refined in-situ monitoring through a 77 m-deep borehole and a 30 m-long trench. Findings reveal that the ground settlement involves both the deformation of the filling loess and the underlying intact loess. Notably, the filling loess exhibits a stronger creep capability compared to underlying intact loess. The deformation along the profile is unevenly distributed, with a positive correlation with soil moisture. Water accumulation has been observed at the interface between the filling loess and the underlying intact loess, leading to a significant deformation. Moreover, the temperature and moisture in the filling loess have reached a new equilibrium state, with their depths influenced by atmospheric conditions measuring at 31 m and 26 m, respectively. The refined investigation allows us to identify critical layers that matter the sustainable development of newly created urban areas, and provide improved insights into the evolution mechanisms of land creation.

Investigation of Empirical and Analytical Methods Accuracy for Surface Settlement Prediction in Train Tunnel Excavation Projects

Investigation of Empirical and Analytical Methods Accuracy for Surface Settlement Prediction in Train Tunnel Excavation Projects

Bayesian updating for ground surface settlements of shield tunneling

Accurate prediction of ground surface settlements induced by shield construction is of great significance for ensuring the safety of shield construction. This paper proposes a ground surface settlement prediction method for shield tunneling based on Bayesian updating. The sequential observation data during the advance of excavation is utilized to update the key soil parameters, leading to a more accurate settlement prediction for the subsequent excavation stages. Response surfaces are constructed to replace the finite element model as the forward models for higher computational efficiency. A tunnel excavation project in Hangzhou, China, is selected to illustrate the effectiveness of the proposed method. The shield excavation face passes through four soil layers, and two soil parameters (i.e., Young’s modulus and friction angle) of these soil layers are selected as random variables to be updated. The results show that the soil parameters can be effectively updated based on the observation data at multiple points and various excavation stages. The predictions of ground surface settlements are improved by using the updated soil parameters. The prediction accuracy of the proposed method increases as more stages of observation data are sequentially obtained and incorporated.