Deep Excavation Engineering Research Articles

Resilience Assessment of Deep Excavation Engineering Systems Based on Bayesian Network

As a key component of infrastructure, the construction safety of deep excavation is particularly important. In order to improve the safety and stability of Deep excavation construction, research on the risk resistance and rapid recovery capabilities of Deep excavation projects is carried out. By introducing the concept of resilience, we analyze the key factors that affect the safety and resilience of Deep excavation projects, use Bayesian networks to establish a resilience model that expresses the causal relationship between factors, and learn the parameters of the network model through data samples collected through surveys; by adjusting the network Analyze the relationship between each factor and system resilience at each node, and clarify the measures that should be taken and key control objects, thereby improving the system resilience and ensuring that normal construction can be carried out safely and orderly. Research shows that this model can be used to quantify the safety toughness value of deep excavation and reason and analyze the impact of various factors on the toughness value, thereby improving risk management and decision support capabilities.

A Semi-Analytical Solution of Two-Dimensional Unsteady Groundwater Flow Outside a Long-Strip Excavation Pit with a Cut-Off Wall

In deep excavation engineering, the implementation of cut-off walls stands as a crucial measure to ensure structural support stability. However, the existing theories for dewatering design often overlook the variations in cut-off wall penetration depths, potentially compromising the efficacy of groundwater control strategies. Addressing this gap, this study conducts a comprehensive investigation into the dynamics of groundwater levels within confined aquifers during the dewatering process of strip excavation pits with cut-off walls. Central to this inquiry is the conceptualization of the entire excavation pit as a singular large-diameter well, with the open part beneath the cut-off wall in the confined aquifer serving as a constant-flux boundary. Employing an advanced analytical modeling approach, the study formulates a robust framework to describe the intricate interplay of unsteady groundwater flow phenomena. Leveraging the techniques of the Laplace and finite cosine transform methods, a semi-analytical solution is derived to elucidate groundwater drawdown patterns over time. The validation of the proposed solution against finite element method results underscores its fidelity and applicability. The parametric analysis reveals a dynamic evolution in drawdown characteristics within the confined aquifer, transitioning from initially cone-shaped distributions to more linear profiles that eventually stabilize with prolonged dewatering. This evolution is governed by the aquifer’s inherent anisotropy and the barrier effect exerted by the depth of cut-off wall penetration. The parametric research also underscores the critical role of lateral boundary distance in influencing groundwater drawdown patterns. The presented solutions can be used to identify optimal penetration depth ratios tailored to specific parameters, thereby offering insights for optimizing dewatering strategies for deep excavation groundwater control. Moreover, a case study was included in this study using the proposed analytical solution, and a comparison was made with field data to validate the practical applicability of the approach.

Digital twin-based quantification of carbon emission from foundation pit construction: A case study of a station in Shanghai Metro

This study focused on achieving the carbon peaking and carbon neutrality goal. A carbon emission calculation method based on the entire process of excavation construction and the emission factor method for the foundation pit construction of a metro station was proposed. This method facilitated quantitative calculation of total carbon emissions in metro foundation pit engineering, which was then incorporated into a self-designed digital twin platform to drive sustainability efforts. The proposed calculation approach was verified in the foundation pit of Huangpi South Road Station (Shanghai Metro Line No. 14). (1) The pit construction process of the targeted metro station emitted 127,439t of carbon dioxide equivalent. (2) From the material perspective, reinforcing steel and concrete accounted for a significant proportion of the overall carbon emissions. Whereas, from the construction perspective, the engineering process of supporting structures accounted for a considerable proportion of the carbon emissions. (3) A comparative analysis of different construction zones revealed that the carbon emissions during the construction stage of the metro pit project were closely related to the amount of earthwork and size of the deep excavation engineering. Practically, the discovered knowledge of carbon emission characteristics can be visualized in a digital twin.

Failure mechanism and deformation forecasting of surrounding rock mass in an underground cavern based on engineering analogy method

The underground powerhouse of Lianghekou hydropower station is deeply buried with high ground stress and complicated geological conditions. To delineate rock mass damage zones and analyze the stability of underground powerhouse subjected to excavation disturbance, an ESG monitoring system was applied to carry out real-time monitoring against the inner micro-fracture activity of surrounding rock mass. In order to solve the problem that the deformation of surrounding rock mass cannot be monitored due to the failure of multipoint displacement meters, the engineering analogy method is adopted to forecast the deformation of surrounding rock mass by comparing the similar projects of Houziyan and Baihetan hydropower stations. Research results show: (1) The failure of surrounding rock mass was stress-driven failure, and was primarily characterized by a medium degree of stress-induced failure. (2) During the monitoring period, microseismic (MS) events clustering area formed, which was both related to blasting excavation disturbance of the bus tunnel and the formed crossed free surfaces. (3) The seismic source parameters during the deformation of surrounding rock mass in similar projects were analyzed, and the variation characteristics of the frequency, energy, b-value, central frequency, apparent stress, and apparent volume of MS events were summarized. (4) The engineering analogy method was adopted to forecast that the deformation period of surrounding rock mass of Lianghekou hydropower station is from April 25 to May 2, 2016. The present achievements can provide some references for similar deep underground excavation engineering.

Mohr–Coulomb and Modified Hoek–Brown Strength Criteria of Layered Sandstone Considering the Unloading Effect and Anisotropy

The Mohr–Coulomb (M-C) and Hoek–Brown (H-B) strength criteria are widely used in various engineering fields, such as mining engineering, tunnel engineering and so on. To investigate the M-C and H-B strength criteria considering the unloading effect and anisotropy, series of triaxial loading (unloading) tests on layered sandstone were conducted. The results revealed that the peak strength was significantly affected by the unloading effect. Moreover, the cohesion and internal friction angle had a significant nonlinear relationship with the bedding angle. Additionally, the M-C and modified H-B strength criteria were established considering the unloading effect and anisotropy. Then, according to the strength criteria established, the peak strength could be estimated theoretically. Furthermore, compared to the M-C strength criteria, the modified H-B strength criteria were more appropriate for accurately estimating the triaxial compressive strength of layered sandstones. The conclusions obtained could provide certain references for the stability control of deep excavation engineering.

Experimental Investigation on Deformation Characteristics of Strutted U-Shape Sheet Pile Flexible Retaining Structures in Excavations Using 3D Printing

U-shape steel sheet piles are widely used in deep and large excavation engineering due to their excellent soil-retaining and water-stopping performances. To achieve deformation control in excavations, an experimental investigation on the deformation characteristics of a strutted U-shape sheet pile flexible retaining structure was conducted. Single-layer and double-layer strutted retaining structure excavation indoor model tests in sand, where U-shape sheet piles were formed by 3D printing, were successfully accomplished. Deformation was monitored in real time during the test. The results show that the lateral displacement mode of the retaining structure transformed with the change in excavation from the “cantilever” to the “bulge” and finally developed into an intricate “recurve bow”. The average maximum lateral displacement was 0.756% of the excavation depth. With a maximum settlement of 0.375% of the excavation depth on average, the distribution of ground settlement behind walls changed from “exponential” to “triangular” before ultimately transforming into “trough” or “trapezoid” mode. The maximum settlement to maximum lateral displacement ratio (smax/δmax) on average was 0.54; the maximum settlement deformation rate was always less than the maximum lateral displacement deformation rate.

Study of Improved Grey BP (Back Propagation) Neural Network Combination Model for Predicting Deformation in Foundation Pits

Deep excavation engineering is a comprehensive discipline that involves multiple fields such as engineering geology, hydrogeology, and foundation engineering. With the improvement of the utilization rate of underground space, the demand for the construction of large-scale underground structural engineering is growing, making the excavation of underground soil become increasingly frequent, which also brings about the safety problems of deep foundation pit engineering and the surrounding environment. Prediction of foundation pit deformation is an important research direction with diverse historical developments, but it is also facing a series of difficulties and challenges. In order to solve these problems, this article proposes an improvement plan, establishes a prediction model based on the combination model of grey BP (back propagation) neural network, and verifies its effectiveness through experiments. The results show that the average error of the new model’s prediction of horizontal deformation is about 0.31, which is about 32% lower than the traditional model’s prediction error. The difference between the vertical deformation prediction and actual monitoring results is also controlled. The vertical deformation predicted by wavelet transform is 7% to 9% larger than the actual monitoring results, meeting the prediction requirements. Finally, this article explores the research on the prediction of foundation pit deformation in deep excavation engineering, An improved grey BP neural network combination model was proposed and its effectiveness was verified through experiments. This article has important reference value for the study of deformation prediction in deep excavation engineering.

Research on Optimization of Deep Excavation Support Scheme Based on Distance Discriminant Analysis Method

With the rapid growth of China's national economy and urban construction, various factors make deep excavation engineering a challenging, high-risk and difficult geotechnical engineering technical subject. It plays an important role in concrete construction and has very high requirements for technology. In deep excavation engineering, in order to achieve the same supporting purpose, there are many alternative schemes, among which each scheme has its own characteristics. The choice of deep excavation support scheme is a complex multi-factor decision-making problem. Based on the idea of distance discriminant analysis theory, considering the principle of distance discriminant analysis method and the specific characteristics of deep excavation support scheme, this article tries to apply discriminant analysis method to the optimization research of deep excavation support scheme, so as to discuss the optimization design of deep excavation support project. It is hoped that the research in this article can further ensure the construction effect of building projects and provide some reference for similar projects.

A Deterministic Method for Evaluating Safety Factor of Deep Excavation Stability against Groundwater Inrush Equivalently Considering Soil Uncertainty

In current design specifications for deep excavation, the determination of safety factors against groundwater inrush only considers the self-weight effect of soil mass at the bottom. However, the shear strength and its spatial variability in a cement-solidified bottom layer also plays an important role in safety factor estimation. Based on that, in this study, the strength reduction method was introduced into reliability analysis of deep excavation engineering, and the influence of shear strength and its spatial variability of cement-solidified soil on the stability of deep excavation is studied. Furthermore, a deterministic analysis method that can equivalently consider soil uncertainty is proposed and verified.

Assessment of Earth Retaining Performance for Long-Short Piles Composite Structures from Field Experiments and Numerical Analysis

Retaining pile structure is commonly utilized in excavation maintenance design. In recent years, the long-short combined retaining piles have received more and more attention. According to the actual deep excavation engineering, the working mechanism of the long-short, long-double-short, and long-triple-short combined retaining piles was tested in the field. Based on the field test parameters, the finite element model of the test area was established and the simulation results were verified, and the effects of short pile length and pile spacing on bending moment, horizontal displacement of piles, surface settlement, and excavation bottom heave were further investigated. The results show that the bending moment of the long pile is larger than the short pile. The bending moment of the long pile and short pile increases gradually with the increase in the number of short piles. When the combination changes from combination 1 to 3, the peak moment of the long pile and short pile increases by 15.8% and 15.2%, respectively. The maximum displacement is near the pile top, combination 3 has the largest horizontal displacement, and the peak displacement of the long pile and the short pile is 17.21 mm and 17.87 mm, respectively, but almost no effect exists on the horizontal displacement below the excavation bottom. In addition, reducing short pile length and increasing pile spacing will increase bending moment and horizontal displacement of the long and short piles to a certain extent, and this phenomenon is mainly concentrated above the excavation bottom, the influence of short pile length and pile spacing on surface settlement and excavation bottom heave can be ignored.

Fractal Analysis of Fragmentation Distribution of Rockbursts Induced by Low-Frequency Seismic Disturbances

Low-frequency seismic disturbances frequently induce violent rockburst hazards, seriously threatening the safety of deep excavation and mining engineering. To investigate the characteristics and mechanisms of rockbursts induced by seismic disturbances, in this study a series of true triaxial experiments, including the moderate seismically induced, the weak seismically induced, and the self-initiated rockburst experiments under different conditions were conducted. The fractal geometry theory was applied to study rockbursts and the fractal dimensions of fragmentation distribution of different types of rockbursts were calculated. The results show that the fragmentation distributions of both the seismically induced and self-initiated rockbursts exhibit fractal behaviors. For the moderate seismically induced rockbursts, as the static stresses (i.e., the maximum and minimum static stresses) and disturbance amplitude increase, the fractal dimension increases, whereas, as the disturbance frequency increases, the fractal dimension decreases first and then increases. Under similar static loading conditions, the moderate seismically induced rockbursts have the largest fractal dimension, followed by the self-initiated rockbursts, and the weak seismically induced rockbursts have the smallest fractal dimension. There is a linear relationship between the average fractal dimension and kinetic energy of these rockbursts, implying that the fractal dimension can serve as an indicator for estimating rockburst intensity. Furthermore, from a fractal point of view, the energy input, dissipation, and release of these rockbursts are all linear processes.

Field Rebound and Recompression Curve of Soft Clay

Abstract During sampling and sample preparation, the soil specimen is disturbed, which is accompanied by a decrease in void ratio, and the stresses within it release from in situ status to a residual one, usually associated with an expansion to some extent. As a result, the in situ void ratio and field recompression index, i.e., ev0 and CFR, change to e0 and CLR, respectively, which have not been properly accounted for in the traditional method. A rebound-recompression method (RRM) is proposed in this article for the derivation of a field compression curve from laboratory compression test results, with techniques being developed to modify these two parameters from laboratory measurements to field ones. This method has the clear advantage that the rebound and recompression behavior prior to the yield stress can be satisfactorily captured. Moreover, criterion to assess the sampling and preparation quality of soil samples is also proposed. This new method is validated against three consolidation tests with differing stress paths. In addition, measurements from an excavation in the field suggest that the RRM yields reliable results and highlight the nonconservativeness of the traditional method in deep excavation engineering.

Performances and Working Mechanisms of Inclined Retaining Structures for Deep Excavations

Because of the limits of struts, braceless retaining structures (BRS) have become a preferred option in deep excavation engineering. A type of BRS, that is, inclined retaining system, has been successfully applied in several projects. However, its performance and working mechanism have not been systematically studied. A case study and finite element results in this study show that inclined piles (IP) are more effective than vertical piles (VP), while composite inclined retaining structures (CIRSs) are more effective than IP in terms of deflection and bending moment reduction. The deformation‐control mechanism of IP mainly comes from the decrease in the active earth pressure. For CIRSs, the working mechanism is governed by several combined effects, that is, the rigid frame effect, inclined strut effect, earth berm effect, and gravity wall effect. For instance, in composite vertical and inward‐inclined piles (VIIP), inclined piles function as struts for the vertical piles in this rigid frame system and frictional force between the soil and the inclined piles significantly influences its retaining performance; the soil between the vertical and inclined piles plays a role similar to an earth berm; additionally, the entire retaining system is similar to a gravity retaining wall, which has relatively high overturning stability.

Pit-retaining Structure Construction Technique of H-shaped Steel Anchor Composite Pile- Prefabricated Wallboard Adopting Compaction Grouting Method of a High-rise Building in Guangzhou

Taking the deep excavation engineering of a tall building in Guangzhou as an example, this paper introduces the pit-retaining structure construction technique of H-shaped steel anchor composite pile- prefabricated wallboard adopting compaction grouting method. The main construction process of this technique includes: (1) surveying setting-out to fix piles’ locations, (2) hoisting piles into place and adjustment, (3) H-shaped steel piles driving, (4) layered and segmented excavation and pile body treatment, (5) layered and segmented drilling anchor stocks one by one from top to bottom, (6) hoisting prefabricated wallboard in position, (7) inserting reinforcement and binding firmly with protruding bar of precast wallboard, (8) layered and segmented high pressure grouting, (9) pouring expansive concrete at joints,(10) repeated step(4) to step (9), (11) steel bar binding of middle beams, framework supporting and concrete grouting, (12) acceptance check. This method utilizes the integral foundation pit enclosure structure formed by the H-shaped steel pile, anchor rod and precast wallboard and the construction follows the principle of layered and segmented excavation, setting anchors step by step and grouting immediately after hoisting, which realize the assembly construction of the foundation pit enclosure structure and can effectively saving time, retain soil and seal water.

MECHANICAL PERFORMANCE OF COMPOSITE RETAINING AND PROTECTION STRUCTURE FOR SUPER LARGE AND DEEP FOUNDATION EXCAVATIONS

The reliable retaining methods and a good stress system are the key to the success of super large and deep excavation engineering. In this paper, the deepest foundation pit in Hainan province is taken as an example. The method of mutual verification between in-situ monitoring and numerical simulation is adopted. The mechanical performance of composite retaining structure composed of reinforced concrete cast-in-situ soldier pile wall, diaphragm wall and prestressed anchor cable are studied. The interaction between the reinforced concrete cast-in-situ pile retaining structure at the upper part and the diaphragm wall retaining structure at the lower part is revealed, and the variation of internal forces of the diaphragm wall retaining structure in the time and space is demonstrated. And then the influence of insertion ratio and rigidity on the mechanical properties of diaphragm wall is discussed. Research shows, the range of interaction between the upper and lower retaining structures is limited. During the excavation process, the maximum bending moment of the diaphragm wall is always near the excavation surface, and the curvature of the bending moment curve decreases gradually with the increase of excavation depth and axial tension of anchor. When the insertion ratio of diaphragm wall increases, the maximum bending moment moves upward. With the rigidity of the diaphragm wall increases moderately, the bending moment of the retaining structure increases, but the lateral displacement decreases. The research results can provide theoretical basis and practical experience for the composite retaining structure design of super large and deep foundation excavations.

Influence of the opening timing of recharge wells on settlement caused by dewatering in excavations

In deep excavation engineering, the head of the confined aquifer below the excavation bottom must be lowered when the anti-uprush safety factor is not satisfied. However, the drawdown of the confined aquifer may cause ground settlement around the excavation and endanger adjacent buildings, tunnels or municipal pipes. Artificial recharge (AR) is a measure that has been applied in such situations to recover the water level and control the settlement. However, practical engineering cases have shown that AR could control only the development of settlement and could hardly recover the settlement caused by long-term dewatering. Therefore, three recharge schemes, namely, “recharge first”, “simultaneous pressure relief and recharge” and “pressure relief first”, are studied using numerical modeling. The results show that the opening timing of the recharge wells and pressure relief wells has a significant impact on the final settlement. In different recharge schemes, different stress paths of the soil in the confined aquifer and overlying aquitards cause different plastic compressive deformations. To reduce plastic deformation, recharge should begin at the same time as pressure relief when the surrounding environment of the deep excavation must be strictly protected. Additionally, the case study and numerical simulation both show that the most significant settlement or uplift occurs in the deep soil layer rather than at the ground surface, a phenomenon that occurs because the vertical displacement of the soil adjacent to the relief and recharge wells is larger than that in the soil far away, leading to a vertical soil arching in the strata above the confined aquifer.

Experimental study on the artificial recharge of semiconfined aquifers involved in deep excavation engineering

Artificial recharge measures have been adopted to control the drawdown of confined aquifers and the ground subsidence caused by dewatering during deep excavation in Tianjin, Shanghai and other regions in China. However, research on recharge theory is still limited. Additionally, confined aquifers consisting of silt and silty sand in Tianjin have lower hydraulic conductivities than those consisting of sand or gravel, and the feasibility and effectiveness of recharge methods in these semiconfined aquifers urgently require investigation. A series of single-well and multiwell pumping and recharge tests was conducted at a metro station excavation site in Tianjin. The test results showed that it was feasible to recharge silt and silty sand semiconfined aquifers, and, to a certain extent, the hydrogeological parameters obtained from the pumping tests could be used to predict the water level rise during single-well recharge. However, the predicted results underestimated the water level rise near the recharge well (within 7 m) by approximately 10–25%, likely because the permeability coefficient around the well was reduced during the recharge process. Pressured recharge significantly improved the efficiency of the recharge process. Maintaining the recharge and pumping rates at a nearly equal level effectively controlled the surrounding surface and building settlement. However, the surrounding surface subsidence tended to rapidly develop when recharge stopped. Therefore, the recharge process should continue and gradually stop after the pumping stops. The twin-well combined recharge technique can be used to control the head loss of an aquifer when one of the recharge wells requires pumping to solve the associated clogging problems.

Experimental Study of an Inflatable Recyclable Anchor

This paper describes an investigation into the performance and pullout capacity of a new inflatable anchor system embedded in deep excavation engineering. The proposed inflatable recyclable anchor system consists of a rubber pneumatic bag, movable steel plate, and force transmission bar, which can all be recycled after use. By conducting a number of field pullout tests, it is found that the pullout bearing capacity of the proposed anchor is related to the inflation pressure, the length of the rubber pneumatic bag, and the embedment depth. It is found that, with the exponential increase of inflation pressure or length of the rubber pneumatic bag, the pullout bearing capacity of the novel inflatable anchor increases exponentially. The proposed inflatable recyclable anchor can meet the bearing requirements of traditional grouted anchors. Moreover, the proposed anchor not only has better supporting effects than traditional grouted ones, but it also has the advantages of recyclability, repeated use, and rapid formation of anchorage force. It is a new green and low‐carbon anchorage, so it will have good application prospects in temporary foundation pit slope engineering.

Optimization of Small Strain Stiffness Parameters in Deep Excavation Engineering

Optimization of Small Strain Stiffness Parameters in Deep Excavation Engineering

Researches on the Influence on Neighboring Buildings by Concave and Convex Location Effect of Excavations in Soft Soil Area

For an irregular shaped excavation, the settlement pattern of soil layers and structures was greatly affected by the concave and convex location. In this paper, a case study of the ShuangXing Yuan deep excavation engineering located in Yingkou, China, is examined to investigate the deformation characteristics of buildings located in concave or convex positions of the excavation. It was found that the affected areas of soil settlement near the concave and convex location were much different from the middle of the excavation. Due to the corner effect, the adjacent building was not only suffered from settlement but also torsional deformation. The settlement pattern in the corner location of excavation is a three-dimensional surface and cracks in buildings induced by significant differential settlement and torsional deformation can appear when buildings are located in the main affected-areas of the corner effect of excavation. In addition, the embedded depth of foundation has a great impact on building settlement at the corner of excavation and it must be considered in the process of excavation design.