Excavation Method Research Articles

Comparative Evaluation of Clinical and Microbiological Assessment of Caries Excavation Using Conventional, Smart Bur, Chemomechanical Method and ErCr:YSGG Laser

ABSTRACT Objectives: Caries removal efficacy in terms of microbiological burden using Tungsten Carbide Bur No. 330, Polymer bur, BRIX 3000, and ErCr:YSGG Laser. Methods: Class I open dentinal caries was selected and divided into four groups (n = 15) depending on caries excavation methods. Group I: Tungsten carbide (TC) No 330-bur; Group II: Polymer bur (Smart bur); Group III: Brix 3000 gel; Group IV: Erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er:Cr:YSGG) laser. Two samples of carious material, before and after caries excavation, were taken and cultured on blood agar plates. Multiple comparison of mean CFUs/ml between different groups was done using Dunn’s post hoc test and Wilcoxon signed-rank test. Results: Group I showed significantly lesser mean CFUs/ml followed by Group IV as compared to Group II and Group III. Conclusion: Within the parameters and limitations of the present study, ErCr:YSGG laser can be a helpful aid as a minimally invasive method of caries excavation.

Application of Integrated Geological and Geophysical Surveys on the Exploration of Chalcedony Deposits: A Case Study on Nanhong Agate in Liangshan, China

Nanhong agate, esteemed for its vivid color and natural shine, is experiencing a scarcity in supply despite its high demand. The primary deposits of agate, typically found near the surface, have not been extensively explored due to the predominance of traditional manual excavation methods. This research examined the Nanhong agate deposits in the Zhaojue–Meigu region of Liangshan, China, employing the integration of geological and geophysical surveys. Field geological surveys allowed us to outline the general areas where agate is found. Following this, using magnetic surveys, vertical electrical sounding, and controlled-source audio magnetotellurics, agate deposits were located within the conglomerate layer of the second member of the Feixianguan Formation from the Lower Triassic period at depths of less than 100 m. Our results identify mineralized layers, Xuanwei Formation mudstone, and the underlying bedrock, thus supporting the creation of a mineral prediction map. This research provides essential insights and guidance for agate exploration and the development of associated mineral resources.

A Case Study of The Performance of A Pile-Supported Bracing Method for Basement Building

Deep excavations in urban areas are highly hazardous due to extensive settling of the surrounding soil, which can lead to the failure of retaining wall systems and the consequent collapse of adjoining properties. The retaining wall and bracing system are important for completing deep excavations for a basement building project. This paper evaluates the performance of an alternative, innovative, low-cost pile-supported bracing system (PSBS) method during excavation for two-level basement construction. Assessed PSBS performance in terms of ground settlement, lateral movement of supporting systems, schedule, and cost comparison. The PSBS excavation method was designed and then implemented to construct a two-level basement using the bottom-up method. The total station was utilized to monitor three-dimensionally, like the adjacent school building, ground surface settlement, and lateral movement of supporting systems. A schedule and cost comparison were performed using internal bracing and the PSBS technique. The recorded filed data was analysed, and it found that the lateral movement of the support system, adjacent building, and ground settlement is within the allowable limit. According to the estimated results, the PSBS method reduces construction time by 272 days compared to the internal bracing system. The PSBS approach is also less expensive than internal bracing for a two-level basement.

Determination and application study of optimal delay time for tunnel millisecond blasting based on interference vibration reduction method

In tunnel excavation, blasting is widely adopted as an efficient excavation method. However, the influence of vibration on tunnel surrounding rock and support structures during the blasting process cannot be ignored. In this study, based on the background of tunnel blasting construction, we theoretically analyze the reasonable range for selecting the optimal delay time, considering the wave superposition cancellation effect and rock fragmentation effect. We use field measured single-hole waveform and calculate superimposed predicted waveforms for different delay time through linear superposition. This allows us to determine the optimal delay time; it is then validated through numerical simulation and field experiment. The results indicate that, based on the principles of interference vibration reduction and rock fragmentation, the optimal delay time in theory should be in the range of 6.14–8.06 ms. By performing superposition calculation on the measured single-hole waveforms, we determined that the optimal delay time for continuous detonation of cut-holes is 7 ms. The delay time of 7 ms falls within a reasonable millisecond range and it is consistent with the results of numerical simulation. When the optimal delay time was applied to field blasting, the measured vibration waveforms exhibited uniform distribution. Compared to blasting without delay, the peak vibration velocity of the cut-holes decreased from 2.08 cm/s to 0.20 cm/s, and the dominant frequency band shifted from 20 Hz–60 Hz to 30 Hz–120 Hz. This achieved the desired effects of reducing vibration and enhancing frequency. These findings can serve as a reference for future similar engineering projects.

Theory and experimental discussion of synchronous backfilling self-compacting concrete technology behind the segment wall of double-shield TBM

The conventional method of urban subway tunnel excavation using a double-shield tunnel boring machine (DS-TBM) typically involves a two-stage backfilling process behind the segment wall using pea gravel and grouting. However, this method has inherent drawbacks such as uneven backfilling of pea gravel and delayed grouting, which can lead to structural issues such as segment dislocation, damage, and groundwater leakage during tunnel excavation. To address these problems, this study proposes a technical theory of synchronous backfilling self-compacting concrete backfilling material (SCCBM), considering the limitations of the conventional DS-TBM backfill method. This theory uses a specially designed wear-resistant seal plate suitable for a DS-TBM shield tail. The optimal proportion of SCCBM for backfilling the segment wall was determined based on Okamura's empirical method using anti-dispersion powder, fine stones (1–5 mm particle size), and coarse stones (5–10 mm particle size) as the basic materials. The SCCBM was designed and evaluated using various test methods, including the mini-slump, standard slump flow, standard L-box, and improved L-box tests. The engineering characteristics of the backfill material, such as initial setting time, blocking ability ratio, stone rate, and axial compressive strength, were considered during the evaluation. The results demonstrate that all indicators meet the standards for backfilling behind subway tunnel segment walls. Furthermore, an on-site synchronous backfilling SCCBM experiment was conducted to validate the feasibility and advantages of the new synchronous backfilling technology. The experiment involved observing the complete backfill process and monitoring the vertical displacement of the segment. Through these observations, the practicality and benefits of the proposed synchronous backfilling technology were confirmed.

Exploring the feasibility of prestressed anchor cables as an alternative to temporary support in the excavation of super-large-span tunnel

AbstractExcavating super-large-span tunnels in soft rock masses presents significant challenges. To ensure safety, the sequential excavation method is commonly adopted. It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages. However, these internal supports generally impose spatial constraints, limiting the use of large-scale excavation equipment and reducing construction efficiency. To address this constraint, this study adopts the “Shed-frame” principle to explore the feasibility of an innovative support system, which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions. To evaluate its effectiveness, a field case involving the excavation of a 24-m span tunnel in soft rock is presented, and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system. The results revealed that prestressed anchor cables integrated the initial support with the shed, creating an effective “shed-frame” system, which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds. Moreover, the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly. In summary, the proposed support system balances construction efficiency and safety. These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.

A deep learning-based surrogate model for probabilistic analysis of high-speed railway tunnel crown settlement in spatially variable soil considering construction process

In reality, many high-speed railway tunnels are built by sequential excavation method in spatially variable soil. This study introduces an efficient deep learning-based solution for the probabilistic analysis of tunnel crown settlements considering the spatial variability of surrounding soil. The two-dimensional convolutional neural network (2D-CNN) is employed to uncover the implicit correlation between the soil elastic modulus random field and tunnel crown settlements. The correlation coefficient (R) of the surrogate model is greater than 0.9664. Meanwhile, the mean relative error of the predictions remains within 2.38%, under various scales of fluctuation (SOFs). An additional 10,000 samples were produced to assess the practical performance of the trained model in probabilistic analysis. The relative errors of predictions generally fall within 5%, with a minimum confidence interval of 98.15%. These results demonstrate that the developed 2D-CNN model can effectively substitute the traditional method in predicting tunnel crown settlements considering soil spatial variability.

Assessment of the efficiency of dental excavation methods using laser speckle imaging.

This paper introduces a novel application of the laser speckle technique in dentistry, focusing on assessing the efficiency of dental excavation methods used to remove decayed tooth structure. The aim is to evaluate the efficiency of two chemo-mechanical agents and the high-speed drill using the laser speckle technique, which offers objective, non-invasive, and real-time evaluation capabilities. Extracted human primary molars with active occlusal carious lesions were sectioned into three parts, with each part allocated to one of three groups: Group 1 (Brix3000®), Group 2 (Papacarie DUO®), and Group 3 (High-speed drill mechanical caries removal). Caries removal was performed using the designated agent or method for each group. After caries excavation, speckle imaging using a 632.8 nm laser was conducted. Additionally, SEM was used to acquire micro-photographs of the surface morphology of the treated samples. The findings reveal insights into the comparative efficiency of the three dental excavation agents and methods using the laser speckle technique. The speckle parameters extracted from speckle patterns generated by treated teeth provide valuable information for evaluating the performance of the excavation methods. The scanning electron microscopy images also offer detailed visual evidence to support the analysis. This paper demonstrates the potential of the laser speckle technique for assessing the efficiency of dental excavation methods. The objective, non-invasive, and real-time evaluation provided offers advantages over subjective visual assessment and manual measurements.

Calculation of Column Pile Heave in Deep Excavation Based on the Rebound–Recompression Method

Excessive column pile heave may result in engineering disasters such as instability of retaining structures and cracking of existing engineering piles in deep excavations. However, factors such as support weight, changeable support restraint resistance, and soil disturbance at the bottom of the excavation are often ignored or simplified in existing calculation methods but have a significant impact on the calculation results. Based on field soil parameters obtained by the rebound–recompression method, a semi-analytical method is proposed for estimating column pile heaves in a deep excavation. This method considers the influence of soil disturbance, the weight of the retaining structure, and the changeable horizontal support restraint, making the calculation result more consistent with the realistic situation. This method can also be used to analyze load transfer between the pile and the surrounding soil. The rationality of this proposed calculation method is verified by measured data, where the variation in pile stress state during deep excavation is analyzed. Finally, a parametric study is conducted, and the results show that the excavation size and the excavation depth have a great influence. However, the heave is hardly affected by the value of the limit relative displacement. The use of long piles with small diameter and the method of small block excavation are effective means to control the column pile heave. When the excavation area is large or the effective pile length is short, the factor of the position of the column pile cannot be ignored.

Mechanised deep tunnel excavation in saturated clayey soils: a pre-design hydro-mechanically coupled method for the assessment of both spoil and face volume loss

Mechanised tunnel excavation in soils causes over-excavations, potentially leading to large amounts of spoil and settlements at ground level. An accurate estimation of over-excavations is crucial in the pre-design phase for assessing costs, determining the appropriate excavation method and choosing the muck management strategy. Currently, the estimation is based on experience and data from similar projects, but this becomes difficult when project conditions are heterogeneous. As an alternative, finite-element analyses are time-consuming and not suitable for early design stages; therefore, simplified tools are needed. In this paper, the authors present a simplified approach putting in relation face extrusion with estimated spoil mass and face volume loss. This approach, conceived for deep tunnels, is the extension to the case of mechanised tunnelling of a hydro-mechanical coupled meta-model derived from finite-element numerical analyses for tunnels in clayey soils excavated by using conventional techniques (i.e. without any use of tunnel-boring machines). The model has been validated against field data relative to a case study. The approach can be used in the early design process to identify tunnel-boring machine characteristics and provide preliminary cost estimates. In addition, during the construction phase, the method can be employed to interpret monitoring data and pre-design mitigation measures for unforeseen soil profile variations.

Shallow tunneling's impact on surface settlements

The research described in this paper deals with the impact of shallow tunneling on surface settlements in urban areas. The study focuses on carrying out a numerical analysis and a parametric geotechnical study to investigate the effects of tunnel excavation on the surface ground, particularly with regard to distortion and potential damage to structures above the tunnel. To carry out the study, the researcher used a finite element method (FEM) software package called Plaxis. This software is commonly used for geotechnical analysis and allows simulating and analyzing the subsurface conditions in Algiers underground in the context of excavating a shallow tunnel. The New Austrian Tunnelling Method (NATM) excavation method was chosen for the study. The results of the numerical analysis are presented in terms of displacements. The results indicate that ground flow has a significant influence on ground movement, probably contributing to surface settlement. However, the effect of tunnel excavation on the lowering of the water table and Young's modulus (a measure of soil stiffness) is relatively small in comparison. The research provides valuable information on the potential impacts of shallow tunneling in urban areas and the factors that play a crucial role in determining the extent of ground movement and surface settlement. By using numerical analysis and conducting a parametric geotechnical study, and gives valuable insights into the potential impacts of shallow tunnelling in urban areas and the factors that play a crucial role in determining the extent of ground movements and surface settlements. By using numerical analysis and conducting a geotechnical parametric study, and contributes to a better understanding of the behavior of the ground during tunnelling operations in Algiers. The findings can be helpful in designing future tunnelling projects to mitigate potential risks to structures and infrastructure located above the tunnels.

Deformation Prediction Model of Existing Tunnel Structures with Equivalent Layered Method–Peck Coupled under Multiple Factors

The existing tunnel structure, the new underpass tunnel structure and the rock strata in the area of influence of the crossover tunnel are interacting systems that are affected by various factors, such as dynamic and static excavation loads and dynamic and static train loads. The existing theoretical models for the deformation prediction of existing tunnels lack the synergistic analysis of dynamic and static loads on both existing and new tunnels. Based on the theory of the current layer method and Peck’s empirical formula, this paper considers the stiffness of existing tunnels, the stiffness of new tunnels, the loads of excavation methods and the loads of existing tunnels. The results show that a theoretical model for the prediction of the deformation of double-lane highway tunnels underneath existing railroad tunnels with the coupling of the current layer method and Peck under multiple factors is constructed; a modified Peck settlement formula for the base plate of the existing tunnels is put forward; and, through numerical calculations and monitoring data for validation and optimization, it is proved that the theoretical model is applicable to the excavation of tunnels underneath mountainous areas mined by the blasting method.

Crack propagation mechanism of smooth blasting holes for tunnel excavation under high in-situ stress

Smooth blasting is an important excavation method in tunnel construction, creating a smooth and even excavation profile during the excavation process. In this study, the influence of in-situ stress, hole spacing, and radial decoupling coefficient on the superposition of blasting stress and the cracking characteristic between holes were investigated by using integrated analytical and numerical analyses (FDEM). Based on those results, the design of smooth blasting parameters considering the influence of in-situ stress were suggested, and verified against the data collected during the blasting excavation of diversion tunnel at Jinping II hydropower station. The results indicated that the propagation of blast-induced fractures are significantly influenced by the insitu stress conditions, tending to extend towards the direction of the maximum principal stress thus the holes should be arranged along the direction of the maximum principal stress to ensure the formation of cracks between holes and smooth excavation of the wall.

Numerical and Preliminary In Situ Investigation on Roadway Excavation Using Static Expansion Mechanical Fracturing

This paper introduced a new nonexplosive roadway excavation method, combining the reserved free space technology and the static expansion mechanical fracturing technology, where the former is implemented by the gasbag, while the piston splitter is for the latter. The numerical model of roadway excavation was set up via PFC3D to investigate the mechanical fracturing performance, including the single-hole fracturing and the hole network fracturing. The results show that the reasonable hole margin is about 1.0–1.5 m, and the optimal column spacing of the hole network pattern is 1.0 m, after comprehensively analyzing the fracturing performance and the splitting force evolution. Moreover, the mechanical fracturing excavation method was applied to construct a parking chamber in the Kalatongke Mine, to preliminarily verify the feasibility of the static expansion mechanical fracturing technology. The in situ investigation results indicate that the excavation footage is about 0.8 m with the piston splitter when adopting a hole margin of 1.0–1.5 m. To sum up, the preliminary field application and the numerical simulation result both support the feasibility of mechanical fracturing, and the reasonable fracturing hole margin is about 1.0 m.

Coupled analysis and simulation of safety risk in subway tunnel construction by shallow-buried excavation method based on system dynamics

To address the existing shortcomings in the research on the coupling of safety risk factors in subway tunnel construction using the shallow-buried excavation method, this paper conducts a coupled analysis and dynamic simulation of the safety risks associated with this construction method. Firstly, by analyzing the mechanisms and effects of risk coupling in shallow-buried excavation construction of subway tunnels, this study divides the risk system into four risk subsystems (human, material, management, and environment), establishes an evaluation index system for the coupling of safety risks, calculates the comprehensive weight values of the risk indicators using the AHP-entropy weight method, and constructs a risk coupling degree model by combining the inverse cloud model and efficacy function. Subsequently, based on the principles of system dynamics, a causal relationship diagram and a system dynamics simulation model for the coupling of “human-material” risks in construction are established using Vensim PLE software. Finally, the case study of the underground excavation section of Chengdu Metro Line 2 is employed to perform dynamic simulation using the established model. By adjusting the relevant risk coupling coefficients and simulation duration, the impact of the coupling of various risk factors on the safety risk level of the human-material coupling system is observed. The simulation results demonstrate that: 1) Heterogeneous coupling of human and material risks has a particularly significant effect on the system’s safety risks; 2) Violations by personnel and initial support structure defects are key risk coupling factors. The findings of this study provide new insights for decision-makers to assess the safety risk of shallow-buried excavation construction in subway tunnel.

Deformation caused by T-shape expansion of existing metro station: complex challenges and strategies

This case study presents an investigation on existing metro station deformation characteristics during T-type expansion in Nanjing, China. A three-dimensional elastic-plastic finite element model is adopted to consider the interaction of soil, retaining structure, horizontal support system and existing station structure. The results indicate that coupling deformation of asymmetric uplift deflection and existing structure rotation occurs on existing structure. Moreover, the sensitivity of influencing factors is analyzed, including the dimension of retaining structure, the support spacing, the excavation method, the soil reinforcement depth in passive area, the width of retaining soil during excavation, the relative position between foundation pit and existing structure, the excavation depth, the existing structure rigidity. Furthermore, based on the analysis of difficulties in the T-shape expansion projects, the controlling measures for the deformation of existing metro station are proposed. The achievements of this case study can be used as a reference for similar underground expansion projects.

Ground Prediction by Markov-ANN Hybrid Analytics Using Baseline Geotechnical Data and Observed Field Data

ABSTRACT Geology along the tunnel length usually differs from the anticipated data as per Geotechnical Baseline Report (GBR), sometimes quite significantly. This has always led to the disruption of the planning, resource mobilisation, cost and duration of the project. One way to minimise this uncertainty is by exhaustive investigation like probe holes and geophysical prospecting. Forecasting or prediction of Geology can also be done by soft computing and analytical methods. Using the analytical tool of the Markov Model and the learning powers of Artificial Neural Networks (ANN) has been attempted in this study. The idea is to build a hybrid model that would combine both capabilities and do a probabilistic prediction of the ground condition ahead of the tunnel face in real time to better suit the site, accommodate complexities and can capture the associated uncertainties. The Geotechnical Baseline Report (GBR) having the initial survey details of the tunnel geology is used to build the Markov Model while the deterministic borehole data in the GBR is used to build the ANN model. Bayesian joint probability theorem is used to update the model with the face observed geological parameters. This hybrid model demonstrated to be a good complement to the physical forecasting methods and the geological uncertainty of a complex and challenging Himalayan region was well captured by the present approach. The window of the prediction was for a region of approximately 250m where it showed a very good prediction of ground class. The model can help in systematic planning and resource mobilisation in a better way and subsequent key decisions for the upcoming excavation method and corresponding support measures.

Cultural Dynamics in the Levantine Upper Paleolithic, ca. 40–33 ky BP: Insights Based on Recent Advances in the Study of the Levantine Aurignacian, the Arkov-Divshon, and the Atlitian

The chrono-cultural sequence of the Levantine Upper Paleolithic went through several major revisions during approximately a century of focused research, each revision contributing to shedding light on the mosaic of cultural entities and the complex social and cultural dynamics composing the Levantine Upper Paleolithic. The current state of research suggests the co-inhabitance of two cultural groups: the Early Ahmarian and the Levantine Aurignacian. Two other cultural entities, the Arkov-Divshon and the Atlitian, are regarded as younger manifestations and were tentatively suggested to relate to the Levantine Aurignacian. This paper presents a research synthesis of two case studies: Manot Cave, located in western Galilee, Israel, and Nahal Rahaf 2 Rockshelter in the Judean Desert. The application of high-resolution excavation methods, alongside detailed documentation of the stratigraphy and site-formation processes and wide-scale radiocarbon-based absolute dating, marked these sites as ideal for chrono-cultural study through the analyses of flint industries. The results indicate a clear distinction between the Levantine Aurignacian and the Arkov-Divshon/Atlitian industries and a chronological overlap between the Arkov-Divshon, Levantine Aurignacian, and possibly with the Early Ahmarian. Subsequently, we suggest another revision of the currently accepted chrono-cultural model: not two, but at least three cultural entities co-inhabited the Levant at ca. 40–30 ky cal BP. This study further suggests an evolvement of the Atlitian flint industries from the Arkov-Divshon and stresses the foreign cultural features of the Levantine Aurignacian. These results were used to construct an updated model of migration and possible interaction patterns.

Mechanical Response and Stability Optimization of Shallow-Buried Tunnel Excavation Method Conversion Process Based on Numerical Investigation

Different excavation methods lead to substantial changes in the relaxation zone of the surrounding rock. The stress characteristics of the support structure become more complex during the process of excavation method conversion. It is essential to design a well-considered construction plan to minimize the disruptions caused by excavation method conversion. This work takes a tunnel in Jiangsu Province, China, as the engineering background and establishes a numerical model for the conversion from the double-side-drift method to the three-bench method. Based on a numerical investigation, this study analyzed the deformation of surrounding rock and the stress state of the support structure during the excavation method conversion. The results showed that excavation method conversion can accelerate the deformation rate of the surrounding rock, causing the support structure to bear greater pressure. This leads to a significant increase in the circumferential stress at the junction of two excavation methods. Setting up a reinforced area during the process of excavation method conversion can improve the stress state of the support structure. Finally, an analysis of the parameters of the reinforced area was conducted, and a reasonable construction plan was proposed. This study can provide guidance for subsequent construction projects.

Comparative anatomy and evolution of the atlantoaxial complex in the fossorial lineage Amphisbaenia (Squamata: Lacertoidea).

The atlas and axis are the first two vertebrae from the cervical series; these two vertebrae are responsible for neck flexion, extension, and rotation movements, while providing insertion points for muscles and tendons. Amphisbaenia is a group of fossorial squamates known for having four distinctive head shapes, which are related to different excavation methods. However, little is known about the relationship between these different digging patterns and the anatomy and evolution of the atlantoaxial complex. In this study, we used computed microtomography data to describe in detail of the atlantoaxial complex for 15 species, belonging to all six current families of Amphisbaenia. Furthermore, we evaluate evolutionary scenarios of selected characters related to the atlantoaxial complex in the most recent phylogeny for Amphisbaenia, using the criteria of parsimony and maximum likelihood. Our results indicate that the evolutionary pattern of the atlantoaxial complex presents a diversification in its morphology that is not always correlated with the shape of the head. This analysis reinforces the hypothesis of remarkable morphological convergences in the evolutionary history of Amphisbaenia. Additionally, some of the characters studied may represent independent evolution through convergence in some cases (e.g., horizontal axis of the neural column) and parallelism in others (e.g., present or absent from the transverse process).