Excavation Stages Research Articles

Study on Design Method of Pile Wall Combination Structure in a Deep Foundation Pit Considering Deformation Induced by Excavation

The technology of pile wall combination in a deep foundation pit is a kind of technology to resist soil and water pressure by using the great stiffness of the retaining pile and basement wall. As a part of basement wall, the retaining pile can reduce the thickness of the basement wall. However, the influence of excavation deformation and the interaction mechanism between the retaining pile and basement wall are ignored in the current design theory of the pile wall combination in a deep foundation pit. Therefore, we proposed a composite structure model of an elastic subgrade beam associated with a continuous beam, and introduced an elastic spring to simulate the interaction between the pile and basement wall. The finite difference equation and calculation method were established to figure out the internal force and displacement of the pile wall combination structure, which was able to accurately calculate the internal force and deformation of the retaining pile during the excavation stage. Based on the above results, further investigation was carried on the interaction between the pile and basement wall during the construction and normal service stage of the basement structure. It was concluded that the basement wall could reduce the lateral displacement on the top of the retaining pile caused by removal of the strut and affect the bending moment of the upper part of the retaining pile among the depth of the basement wall. The bending moment of the basement wall was closely related to the deformation of the retaining pile and changes with the working condition. In addition, the results of factor sensitivity analysis showed that the pile-wall relative stiffness ratio, stiffness of the horizontal beam, and slab of the basement had a significant influence on the interaction between the pile and basement wall.

Random forest-based predictors for driving forces of earth pressure balance (EPB) shield tunnel boring machine (TBM)

During the design and excavation stage of the shield tunnel, the prediction of driving forces is pivotal, especially in complex strata. The accuracy of theoretical models for driving loads calculation is insufficient, owing to the academic hypothesis and parameter setting deviation. In this regard, a load prediction approach of an earth pressure balance (EPB) shield tunnel boring machine (TBM) based on a machine learning method (i.e., random forest, RF) was developed. Geological conditions and shield operational data were chosen as features to build the prediction models. The models were then applied to the thrust and torque prediction of an EPB shield TBM in a soil-rock mixed-face ground. The application effect of the RF-based method was evaluated by the coefficient of determination (R2) and the root mean square error (RMSE). Then we discussed the transferability of the built RF model for other EPB shield projects. The results showed that the load prediction capacity of the approach based on the RF algorithm was more accurate than that of theoretical models. Variables importance analysis took the decrease of the mean square error (MSE) as an evaluation indicator. The cover depth of the tunnel ring, the foam quantity, the advance rate, and the rotation speed of the screw conveyor were the top four most influential features for the RF-based thrust and torque prediction model. Overall, this study provides a valuable reference for the safe and efficient EPB shield tunnel excavation in the soil-rock mixed-face ground.

Evaluation of Applicability of 1D-CNN and LSTM to Predict Horizontal Displacement of Retaining Wall According to Excavation Work

During excavation works in downtown, stability and safety considerations of such excavations and constructions are crucial for which continuous wall structures with varying structural components are commonly used. Most of the current models used for this purpose are often complex, where the accepted parameters do not have a clear physical meaning. Moreover, accurate ground movement forecasts are challenging due to nonlinear and inelastic soil behavior. Therefore, this study proposes a method to predict the lateral displacement of the braced wall at each stage of excavation by using all the basic information necessary for braced wall design, including ground information of the excavation site, support methods such as the type of brace, location and stiffness, information about the neighboring buildings, and the results of numerical analysis. One-dimensional convolutional neural network and long short-term memory network are used for estimation and prediction to develop an optimal prediction model based on well-refined but limited data. The applicability of the braced wall was confirmed for safety management by predicting the horizontal displacement of the braced wall for each stage of excavation. The proposed model can be used to predict the stability of the horizontal wall for each excavation step and reduce accident risks, such as collapse of the retaining wall, which may occur during construction.

Прогноз дополнительных деформаций зданий и сооружений в процессе высокочастотного вибрирования шпунтовых свай

The main criterion of safe construction for the underground space development in conditions of dense urban environment is the right selection of enclosing structure of the excavation pit. One of the most common types of the pit enclosing designs is a construction of metal sheet piles driven by high-frequency vibratory loading. It is generally believed that the technology of high-frequency vibratory loading and extraction of piles has no significant impact on the surrounding soil mass and structures of buildings and facilities located in the active dynamic zone. However, numerous examples of additional deformations of buildings emerging even before the stage of the pit excavation starts, witness, that the technological settlement can be as significant as 3-5 cm. The author presents some methods of analytical and numerical forecasting of additional deformations of buildings located in the zone of influence in the process of vibratory driving or extraction of piles based on the hypothesis of vibration-caused creep of dispersed soils. A large amount of deformation is due to the complicated engineering and geological conditions of St. Petersburg. It is in the thickness of weak water-saturated clay soils of soft-plastic, flowable-plastic and flowable consistency that the greatest values of additional deformation can develop. Verification of the developed methods is confirmed by comparing the calculation data with the results of monitoring the values of additional deformations.

Meteorite impact craters as hotspots for mineral resources and energy fuels: A global review

The ever-increasing recovery rate of natural resources from terrestrial impact craters over the last few decades across the globe offers new avenues for further exploration of mineral and hydrocarbon resources in such settings. As of today, 60 of the 208 terrestrial craters have been identified to host diverse resources such as hydrocarbons, metals and construction materials. The potential of craters as plausible resource contributors to the energy sector is therefore, worthy of consideration, as 42 (70%) of the 60 craters host energy resources such as oil, gas, coal, uranium, mercury, critical and major minerals as well as hydropower resources. Among others, 19 craters are of well-developed hydrocarbon reserves. Mineral deposits associated with craters are also classified similar to other mineral resources such as progenetic, syngenetic and epigenetic sources. Of these, the progenetic and syngenetic mineralization are confined to the early and late excavation stage of impact crater evolution, respectively, whereas epigenetic deposits are formed during and after the modification stage of crater formation. Thus, progenetic and syngenetic mineral deposits (like Fe, Ni, Pb, Zn and Cu) associated with craters are formed as a direct result of the impact event, whereas epigenetic deposits (e.g. hydrocarbon) are hosted by the impact structure and result from post-impact processes. In the progenetic and syngenetic deposits, the shock-wave induced fracturing and melting aid the formation of deposits, whereas in the epigenetic deposits, the highly fractured lithostratigraphic units of higher porosity and permeability, like the central elevated area (CEA) or the rim, act as traps. In this review, we provide a holistic view of the mineral and energy resources associated with impact craters, and use some of the remote sensing techniques to identify the mineral deposits as supplemented by a schematic model of the types of deposits formed during cratering process.

Dynamic Risk Assessment of Ultra-Shallow-Buried and Large-Span Double-Arch Tunnel Construction

Ultra-shallow-buried and large-span double-arch tunnels face complex risks during construction. The risk sources are hidden, complicated, and diverse. The dynamic risk assessment problem cannot be solved satisfactorily by using the static method as an insufficient amount of research has been conducted. The land part of the Xiamen Haicang double-arch tunnel was selected as the background for the dynamic risk assessment of ultra-shallow-buried and large-span double-arch tunnel construction. The construction process was divided into five stages: pre-construction preparation; ground and surrounding rock reinforcement; pilot tunnel excavation; and the single-and the double-tunnel excavations of the main tunnel. Through consultation with tunnel experts, six first-level and thirty second-level risk evaluation indexes were proposed. The benchmark weight of the dynamic risk assessment index was determined by using the analytic hierarchy process. The weight of the risk evaluation index was revised according to the monitoring data and the construction stage. The fuzzy evaluation matrix of the construction risk membership degree was obtained by using the fuzzy comprehensive assessment method, and the calculation results were analyzed using the subsection assignment method. Control measures were suggested according to the risk assessment results. The risk assessment result of the double tunnel excavation stage of the main tunnel was level II, and the risk level was the highest among the five construction stages. The risk assessment result of the ground and surrounding rock reinforcement stage was level IV, and the risk level was the lowest. The dynamic construction safety risk assessment based on the fuzzy comprehensive assessment method is more timely, accurate, and reasonable than the traditional assessment method. The method can be adopted in similar engineering projects.

Time-Dependent Behavior of Saint-Martin-La-Porte Exploratory Galleries: Field Data Processing and Numerical Modeling of Excavation in Squeezing Rock Conditions

Field monitoring programs (e.g., convergence measurements and stress measurements in the support system) play an important role in following the response of the ground and of the support system during and after excavation. They contribute to the adaptation of the excavation and support installation method and the prediction of the long-term behavior. In the context of the Lyon–Turin link project, an access gallery (SMP2) was excavated between 2003 and 2010, and a survey gallery (SMP4) has been excavated since 2017. Both tunnels are excavated in Saint-Martin-la-Porte (France) across a strongly tectonized Carboniferous formation, which is highly fractured and heterogeneous. Squeezing behavior has been observed and led to the instability of the support system and of the tunnel face in various locations. Based on the knowledge gained from field data processing and numerical modeling in SMP2, new field data are analyzed for SMP4, which is excavated at a much deeper depth, with a different orientation and with different excavation methods. Numerical modeling of the various profiles of SMP4 considering the excavation stages and the specific yielding support is presented, which predicts the time-dependent response of the tunnel.

Vivienda colectiva en lotes urbanos: seguridad e higiene en obra. Aportes para la gestión de excavaciones, submuraciones y demoliciones

In Argentina, public policies related to Safety and Hygiene started at the beginning of the 20th century, and it was not until the 1970s that the first regulations related to the subject were passed, when the current Law Nº 19587 on "Safety and Hygiene at Work" was sanctioned. In particular, the construction industry, since 1996, has had a complementary regulatory framework with Decree Nº 911. On the other hand, the demolition, excavation and submurder stages found an intervention mechanism with SRT Resolutions Nº 550/11 and SRT Nº 503/14. However, the regulatory framework does not provide specificity in relation to procedures and consequently does not guarantee efficiency/effectiveness in operational terms. This work exposes a gap, which, from a particular methodological approach, concludes with the obtaining of results, as it verifies the levels of compliance of the actions in the traceability of the work, aimed at framing the demolition, excavation and submuration tasks according to regulatory parameters of Health and Safety established by the instrument of analysis / matrix. As part of the final considerations, this work proposes to contribute with management guidelines for the aforementioned tasks in urban collective housing works.

Probabilistic Analysis of Tunnel Roof Deflection under Sequential Excavation Using ANN-Based Monte Carlo Simulation and Simplified Reliability Approach

Tunnel roof deflection is an important measure to control the safety of excavation activity, especially for large-section tunnels using the sequential construction method. A three-dimensional (3D) model of a sequential excavation project in the Lijiaping metro tunnel, Chongqing, China, was developed and the maximum tunnel roof deflection was calculated deterministically at the end of each excavation stage. By defining the characteristics of the soft rock layers surrounding the tunnel section as the random variables, a probabilistic analysis was conducted and the problem was formulated as a reliability model. Two different approaches were used to solve the established reliability problem. One entails an artificial neural network (ANN) trained by a large data set obtained from numerical simulations and then accompanied by the Monte Carlo (MC) sampling method to calculate the probability. The other is a simplified reliability approach using a small data set to approximate the exceedance probability via a regression-based algorithm. The proposed ANN-based metamodel used in the first method could accurately predict tunnel roof deflection and replace the software simulator. Subsequently, the probabilistic results obtained from this method following MC sampling could well converge and provide the probability with enough accuracy. Interestingly, the simplified approach with more than 40 random samples can also provide acceptable results, which provides an economical approach to estimate the exceedance probability.

Study on the Earth Pressure during Sinking Stage of Super Large Caisson Foundation

End resistance is a dominant variable in the sinking process of super-sized caisson foundation, which is of great importance to the safe sinking of the caisson foundation. Based on soil excavation process of super large caisson foundation of the main tower of Changtai Yangtze River Bridge, the distribution characteristics and variation of earth pressure under the foot blade was analyzed using 3D finite element method at the first stage of soil excavation. Furthermore, the earth pressure was monitored in real time during soil excavation in order to analyze the influence of soil excavation process on the distribution of earth pressure. The analysis results of engineering practice showed that in the process of soil excavation from inner area to outer area, the end resistance of inner bulkhead and inner partition walls decreased, while the end resistance of outer bulkhead and outer partition walls gradually increased till the soil reached the failure state in the outer bulkhead area. The distribution characteristics and variation of the earth pressure can really reflect overall stress state of caisson foundation, which helps guide the safe sinking by soil excavation.

Deformation characteristics and failure evolution process of the existing metro station under unilateral deep excavation

With the rapid development of underground space construction, there are more and more large-scale deep foundation pit projects on one side of the metro station. Unilateral deep excavation will result in an imbalance of the earth pressure on both sides of the existing metro station, which is a major engineering risk. Therefore, considering the station width and the excavation depth, this study focuses on the deformation characteristics and failure evolution process of the existing metro station structure caused by unilateral excavation based on the physical model test and discrete element method (DEM) analysis. This research shows that the lateral deformation of the top of the station caused by unilateral excavation is the most significant. Secondly, as the excavation depth increases and the station width decreases, the increase rate of the station overall inclination and lateral displacement becomes more significant. Thirdly, the structure fails when the excavation depth is 5/6H (H is the station height). Then the station instability leads to three disturbed regions in the adjacent stratum. The contact force between soil particles in the disturbed region is small and the stability is poor. Finally, the failure evolution process of the existing station under unilateral excavation is divided into three stages: (a) when the excavation depth is 0–1/2H, the soil and structure are stable; (b) when the excavation depth is 1/2–3/4H, the lateral deformation and inclination of the station reach the security warning range; (c) when the excavation depth is 3/4–1.0H, the structure is unstable and slips laterally, resulting in the ground collapse and local soil extrusion failure. This study reveals the risks of the existing station at different excavation stages, which can make risk prediction for the construction of the project.

Diaphragm wall retaining system – a simplified model for design loads

ABSTRACT Diaphragm walls are the ideal solutions for constructive utilisation of underground space to surmount the space constraints causing hindrance to infrastructural developments in urban areas. Accurate analysis methods to determine the wall forces and deformations are vital for the safe and cost-effective implementation of diaphragm wall projects. This paper describes a simplified method formulated for the analysis of diaphragm walls to process design values. The developed methodology is a combination of the net pressure method, the apparent pressure method and the limit equilibrium concept, with modifications to mitigate the demerits of each method towards the applicability for diaphragm walls. The design values for each excavation stage of a diaphragm wall supported excavation acted upon by any loading condition and ground water level can be computed with the methodology. Formulations for determining vertical axial forces are developed from the basic concepts of pile foundations by modifying the expressions to integrate the specific requirements of diaphragm walls. The developed formulations are validated against numerical analysis with Plaxis by comparing wall internal forces and axial strut forces. Around 90% of the results were found to have a percentage variation of less than 10% compared to Plaxis results, indicating the suitability of the method for application to diaphragm walls.

Numerical Simulation of Soil Displacement and Settlement in Deep Foundation Pit Excavations Near Water

Advancing urbanization in China requires large-scale high-rise construction and underground transportation projects. Consequently, there is an increasing number of deep foundation pits adjacent to water bodies, and accidents occur frequently. This study uses a numerical simulation method to study the stability of the deep foundation pit near water based on the Biot three-dimensional seepage-stress coupling model, with the open-cut section on the south bank of the Jinan Yellow River Tunnel Project as the engineering field test. This indicates the following: (1) the maximum horizontal displacement of the diaphragm wall occurred in the fifth excavation stage, and a horizontal brace effectively controlled the inward horizontal displacement of the foundation pit; (2) considering the effect of seepage in the soft soil foundation, the maximum vertical displacement of the ground surface at each excavation stage occurred adjacent to the underground continuous wall. As the depth of the foundation pit increased, the vertical surface settlement decreases gradually in the direction away from the excavation face; (3) considering the seepage conditions, within each interval of excavation of the foundation pit, the horizontal displacement of the continuous underground wall and ground settlement declined; and (4) the numerical simulation and field monitoring data were in good agreement. Under the conditions of accurate model simplification and parameter selection, numerical simulations can adequately forecast conditions of the actual project.

Mindlin solution on ground deformation caused by the trench excavation during installation of concrete diaphragm wall panels

Concrete diaphragm walls (CDWs) are widely used as support of deep excavation in soft ground in urban areas. Ground deformation occurs during the excavation of trenches for the installation of the CDW panels due to ground stress release. This paper investigates the ground deformation during slurry trenching using Mindlin solution. The pressure of slurry used to protect the trench stability during excavation is simulated as a triangularly distributed load on the trench walls, the soil stress state is solved using Mindlin solution, and the horizontal and vertical ground displacement are obtained through integral transformation of ground strain. The rationality of the solution is verified through comparison between the analytical solution and field measurement. Sensitivity analyses are performed on soil elastic modulus, Poisson's ratio, trench excavation depth and panel length. Simplified formulation is proposed for the prediction of horizontal ground deformation. The impact of excavation stages and adjacent panels on the ground deformation is explored. The study finds that the Mindlin solution is able to provide an approximate solution on the ground deformation during slurry trenching, and the simplified formulation can be used to provide a fast estimate of the horizontal ground movement in engineering practice.

Evaluation of collapse mechanism and portal interaction of a High-Speed Railway Tunnel (T29 Tunnel, Turkey)

Within the scope of the Ankara-Istanbul High Speed Train Project, the T29 tunnel was opened to traffic after completing excavation and support implementation. The tunnel was excavated in weak to very weak graphitic schists causing severe face stability problems and deformations on the tunnel supports during excavation stage. In the progress of the excavation stage, a serious face failure occurred at Km: 225 + 784, and the effects of this face failure were observed on the surface. Since the cover thickness is approximately 35 m in this section of the tunnel, it was decided to pass this zone with a cut and cover structure. The portal excavation was carried out from the failure zone, and it was planned to provide stability with the closure of the surface by constructing a cut-and-cover structure immediately afterwards. However, slope failures occurred during the portal excavations. This section was reworked, and it was decided to support this area with a pile system. Consequently, in this study, the reasons for the face failure and slope failures are investigated, and the construction stages are explained and discussed.

New Physical Model to Study Tunnels in Squeezing Clay-Rich Rocks

Abstract Squeezing ground conditions in tunnels are often associated with rock mineralogy, strength, ductility, excavation sequence, and the magnitude of in situ stresses. Numerous methodologies and empirical correlations have been proposed in the past to determine the level of ground squeezing conditions in tunnels, but most of them are problem specific and limited in scope. This paper presents a fundamental study of tunnel squeezing using a novel experimental approach to simulate tunnel boring machine (TBM) excavation in squeezing ground conditions. The proposed experimental setup employs a cubical specimen of synthetic mudstone, with each dimension being 300 mm and the six faces subjected to a true-triaxial state of stress, with different magnitudes of principal stresses and stress levels that correspond to realistic in situ conditions. A miniature TBM was designed, fabricated, and used to excavate a tunnel into the host rock (specimen) while the rock was subjected to a true-triaxial state of stress. Embedded strain gauges and acoustic emission sensors, which were coupled on the surface of the rock specimen, were also used to monitor the tunnel’s response during the excavation stage. The results from the experiment confirmed the capability of the physical model to provide a better understanding of tunnel squeezing and to delineate the damage and the deformation that occurs during instant stress release and creep behavior of rock around the tunnel boundary during tunnel excavation.

Investigation of piled behaviour due to an adjacent excavation: 3D numerical modelling

Zameer Ahmed Channaret al.,InternationalJournal of Emerging Trends in Engineering Research, 9(6), June 2021, 683–689683ABSTRACTIn congested cities, excavations are unavoidably constructed adjacent to high rising building supported by piled raft foundations which reduces differential settlements in the buildings. Since the excavations inevitably induce soil movement and stress changes in the ground, it may cause differential settlements to nearby piled raft foundation. In this numerical study, a 3D coupled consolidation numerical analysis (using a hypoplastic model, which considers strain dependent and path-dependent soil stiffness) was conducted to investigate a (2×2) piled raft responses to an adjacent 25-m deep excavation in saturated clay. The computed results have revealedthat the rate of piled raft settlement increased significantly beyond excavation stage h/He=0.5. This is because of the degradation of stiffness of clay with strain due to excavation-induced stress release. Differential settlement (i.e. tilting) was induced in the piled raft due to non-uniform stress release.Owing to separation of the raft from the ground due excavation, some of the working load was transferred to the four piles. The maximum positive bending moment was 200 kNm at Z/Lp=0.67. However, no any bending moment was induced in both the piles at the toes.

Adaptive prediction of wall movement during excavation using Bayesian inference

In underground construction works, uncertainties and insufficient information about the underground environment lead to inaccurate predictions of soil-structure interactions. Supported excavations are often over-designed, which underscores a significant potential for cost optimization. However, the uncertainties exist, and the traditional design process does not allow for leaner designs at the start of the project. The emergence of advanced analysis tools enables the development of an Observational Method based approach for a decision-making process in which data can be best utilized to deliver real value, confidence, and control.An automated back analysis approach based on Bayesian inference is developed in this paper and validated with a synthetic case study. Probabilistic modeling and Markov Chain Monte Carlo simulation are used to deliver estimates of soil parameters for a given a geotechnical model, update the prediction of future excavation stages, and fully quantify uncertainties from the constructed model and measurements. Sensitivity analysis is used for model selection to achieve modeling robustness. The impact of prior engineering knowledge about the soil properties on the precision of the predictions is also examined. This approach significantly improves the efficiency of back analysis in current practice and provides a tool for data-driven decision making of design optimization during construction.

The influence of bottom-up anchors pre-tension optimization on the prediction of pit walls rockfall displacements

Introduction. Currently in Russia, innovations in urban subsoil facilities construction are among the key factors of economic development. To improve the efficiency of holding a pit wall in restraint urban conditions and prevent soil loosening around the pit, it is proposed to optimize the pre-tension forces of the bottom-up anchors. It has been determined that the pre-tension forces of the active anchors create extra retention forces in the sliding wedge and, in some specified sense, reinforce the walled soil. Research methodology. When modeling the complex calculation of a pit wall, 4 main stages of the pit excavation and 3 stages of preliminary level tensions of anchor ties were preset. The numerical solution of the beam bending problem is the basic method of calculating the walling strength; the beam laying on the elastoplastic base and retained by the anchors as bonds. The bottom-up anchor structure is modeled in the operating environment of GeoWall software. The values of bottom-up anchors pre-tension are set following the ordinates of forces in the anchors, obtained from the walling stability calculation by the deterministic approach. Experimental research was carried out of the impact made by pit opening stages on the walling stress strained state. Results. Analysis and discussion. The efficiency of bottom-up anchors optimal pre-tension, according to the research results, is obtained by constructing the diagrams reflecting the correlation dependence between the anchors loading and the walling displacement. An obvious advantage of the software is the opportunity to calculate walling and retaining structures stage by stage ignoring their construction technologies. Experimental calculation in GeoWall has shown a high bearing capacity of the bottom-up anchor support. Summary. The nature of the obtained dependence between the anchor longitudinal forces and the pit walling horizontal displacement reflects the actual situation. Thus, for a quiet expectable value of horizontal displacement, it is required to correct the optimal value of pre-tension using the empiricalformula dependences.

Morphologic mapping and interpretation of ejecta deposits from Tsiolkovskiy crater

AbstractHigh‐resolution images and elevation data sets from the Lunar Reconnaissance Orbiter along with spectral data from the Clementine mission are used to identify and map in detail the well‐preserved Late Imbrian Tsiolkovskiy crater situated on the far side of the Moon. This study identifies five distinct morphologic units associated with Tsiolkovskiy crater and the surrounding ejecta blanket. Analysis of the spatial and stratigraphic relationships of each of the ejecta units shows an asymmetrical distribution of the overall ejecta blanket, as well as a consistent overprinting of ballistic ejecta by ponds and flows of impact melt‐bearing material. This study shows that the asymmetric distribution of the ejecta blanket, including a distinct up‐range “forbidden zone,” is related to the impact direction and angle for the impactor that formed Tsiolkovskiy crater. The consistent presence of melt‐bearing ponds and flows overlying the ballistic ejecta deposits indicates that two separate ejecta emplacement events occurred. We interpret this as an initial phase of ballistic ejecta emplacement during the excavation stage, followed by a second phase of melt‐bearing ejecta emplacement. The second phase begins during the end of the excavation stage and continues throughout and beyond the modification stage of crater formation.