Vertical Excavation Research Articles

Novel Application of a Swift-Assembled Support Method with Prefabricated Corrugated Steel for Vertical Shaft Excavation in a Metro Station

For the construction of a subway station, temporary vertical shafts were commonly used to facilitate machine operation. In densely urban areas, the requirement of settlement control and environmental impact called for a novel construction method of vertical shafts. In this paper, a novel swift-assembled support (SAS) structure and construction method for vertical shafts of a metro station was proposed, using prefabricated steel components. A comprehensive scheme of full-time monitoring was conducted to evaluate the performance of this novel support structure and ground response. Field monitoring results indicated that the SAS method was able to control the settlement of ground and adjacent buildings. Based on the field measurements, the calculation theory for design parameters were discussed. The active earth pressure yield from the method considering wall movement was closer to the field measurements. All of the local buckling values were both overestimated based on the technical standards’ methods. The calculation methods were thereby adopted carefully to determine the designed loading share ratio of structure components. The advantage of the SAS method, including rapid construction, safety, and lower environmental impacts, were obviously clear.

Impact of excavation footage on vertical shaft lining deformation and surrounding rock stress in Xiyu conglomerate

The Xiyu conglomerate, which is extensively distributed in Xinjiang, China, presents challenges for vertical shaft construction owing to its poor cementation and low strength. The selection of an appropriate footage length is paramount for ensuring safe construction. Based on the shaft pipeline construction project of the Xinlongkou Hydropower Station on the Kuitun River, this study investigated the impact of footage length on the stability of vertical shafts within the Xiyu conglomerate strata using finite element simulation and measurement data to analyze the lining displacement and change in stress in the surrounding rock. The results show that the excavation footage has little effect on the lining’s horizontal displacement during vertical shaft excavation. A mathematical model was developed to describe how the vertical displacement of the lining varies with the excavation footage and vertical shaft depth. Below a critical threshold, the stress in the surrounding rock cannot be effectively alleviated, leading to a concentration of stress; above that critical threshold, an excessively large excavation increases the load on the surrounding rock. Based on the simulation results and factors such as economic benefits, construction speed, and safety, an excavation footage of 4 m is judged to be appropriate.

Stability analysis of deep foundation pit with a double-row cast-in-place piles and diagonal steel lattice braces under sloped excavation conditions

Existing deep foundation pit support structures are commonly composed of external earth-retaining structures, internal horizontal bracings, and vertical columns. A closed bracing system, often formed by a horizontal support through a bracket board, frequently impedes vertical excavation and soil removal operations in the foundation pit, and the processes of assembly and dismantling are complex and time-consuming. This study presents a combined support system and construction method consisting of cast-in-place piles and diagonal steel lattice braces. For sloped excavation, diagonal braces were constructed by slotting through the reserved soil, allowing the use of a single layer of support within the excavation depth. This approach significantly optimizes the construction process, reducing both project duration and overall cost. The field monitoring results indicated that the support method effectively controlled the lateral displacement of the pile bodies. Field monitoring results demonstrated that the proposed support system effectively controlled the lateral displacement of the pile bodies. The adoption of a support-first, excavation-second approach significantly controlled the settlement of the ground surface around the foundation pit, thereby preventing excessive increments in the axial force of the supports due to the large longitudinal depth excavation. The calculation results of the three-dimensional finite element model for foundation pit excavation and support indicate that the proposed support method results in a decreasing ratio of the maximum lateral deformation depth of the pile body, denoted as δh-m, to the excavation depth He as the excavation depth increases. This implied that the displacement of the pile body was strictly controlled. When the depth of the foundation pit excavation exceeded 10 m, the maximum lateral deformation occurred below 10 m along the pile shaft. The diagonal steel lattice braces transferred the load to the top of the cast-in-place piles at the bottom of the pit, where the stress concentration occurred. During construction, special attention must be paid to the strength of the connection between the pile top and the connecting beams.

Mechanical Response in Existing Structure under Varied Subsurface Excavation Techniques

With the slowdown of urban incremental construction in China, reinforcement and renovation of existing buildings have become a hot topic in the fields of engineering and theoretical research. Underpinning pile foundations and underground excavation are commonly used methods for foundation renovation and reinforcement in existing buildings reinforcement and renovation projects. Nevertheless, there remains a dearth of relevant research concerning the effects of different excavation methods on the stability of existing structures during foundation reinforcement and underground space excavation. In the context of existing building pile foundation underpinning and underground excavation, this paper adopts a numerical simulation research method based on the modification of experimental model parameters, and it compares the overall stress changes and settlement of the underpinning pile foundation and the building under two modes of lateral and vertical excavation. The results indicate that there is a good agreement between the stress and settlement changes of the components in the indoor model experiment and the finite element simulation. Both excavation methods show that lateral and vertical excavation will generate maximum stress on the bottom components of the upper structure and the upper part of the pile. In terms of differences, vertical excavation will cause greater overall settlement of the building, but the settlement in different areas is basically the same. On the other hand, lateral excavation will have smaller overall settlement but may cause the structure to tilt. At the same time, lateral excavation will cause greater stress changes in the columns in the structure. Based on these findings, relevant engineering suggestions are provided to choose different excavation methods and strengthen existing buildings.

Study on the critical stable height of vertical excavation in rocky foundation pit within layered structural plane

The structural plane characteristic was the most critical factor for determining the self-stability ability of deep foundation pit vertical-rock-wall in layered rock stratum. Multiple methods such as model testing, numerical calculation, and theoretical calculation were utilized comprehensively in this paper. The self-stabilizing control effect on the deep foundation pits vertical-rock-wall that under the different structural plane inclination angle (α) and under the different structural plane strength was systematically studied. The results indicated that the overall variation trend of "Sharp decrease ~ Slow decrease ~ Slow increase ~ Sharp increase" in the symmetrical distribution for the self-stability critical height (Hcr) varied with the gradually increasing of α was presented. Meanwhile, the variation trend of "continuously decreasing and rapidly decreasing first, and then slowly decreasing and tending to stabilize" with the structural plane strength reduction coefficient (k). The key factor to control the self-stability of the deep foundation pit vertical-rock-walls lied in fully grasping and utilizing the basic characteristics of rock structural planes. The research results of this paper provided the theoretical basis for scientifically determining the safety level and designing reasonable support structures of the deep foundation pit vertical-rock-walls in layered rock stratum.

Application of super large and deep diameter assembly shafts in soft soil layers

Considering the background of the Shanghai Jing’an Smart Garage Project, first, we introduced the world’s largest vertical shaft boring machine, which was suitable for vertical shaft excavation of diameter 12∼23 m. Then, we expounded the design points and key technologies of super large and deep diameter assembly shafts in soft soil layers. Finally, we verified the applicability of the vertical shaft boring technology in soft soil layers in Shanghai through on-site measurement results. It was observed that this technology had a minimal impact on the surrounding environment, indicating its potential for widespread applications in the coming years.

Effect of Sleeping Position on the Retinal Nerve Fiber Layer in Individuals with Glaucoma.

To evaluate the effect of sleeping in the lateral decubitus position on the average thickness of the retinal nerve fiber layer (RNFL) in the peripapillary region of the optic nerve since the effect of posture on intraocular pressure (IOP) and glaucoma progression is not yet sufficiently understood. A cross-sectional observational study was carried out with 40 volunteers who preferably slept in a right lateral decubitus (RLD) (RLD group N = 20) and left lateral decubitus (LLD) (LLD group N = 20) position. IOP was measured in both eyes, first in the sitting position and again after 10 minutes in a supine position, right lateral, and LLD, respectively. The mean thickness of the RNFL and the vertical papillary cup were measured by optical coherence tomography. The average age of the volunteers was 60.53 ± 7.26 years. There were 32 female and eight male. There was an increase in IOP with the change from the sitting position to the lateral decubitus of 2.7 and 3.6 mm Hg in the RLD group (p < 0.001) and an increase of 3.0 and 3.15 mm Hg in the LLD group (p < 0.001), right eye (RE) vs left eye (LE), respectively. However, there was no difference in IOP values between the groups. The average thickness of the RNFL was in the RLD group-75.10 vs 78.05 μm (p = 0.325) and in the LLD group-81.55 vs 79.95 μm (p = 0.580). Vertical papillary excavation was in the RLD group-0.70 vs 0.65 (p = 0.175) and in the LLD group-0.65 vs 0.65 (p = 1.000), RE vs LE, respectively. We found no relationship between the lateral decubitus position when adopted preferentially for sleeping and the reduction of the RNFL. Search for risk factors for the asymmetrical development of glaucoma, especially in well-controlled IOP in daytime measurements. Vaz RT, Montenegro AAL, Quintas Segundo ADS, et al. Effect of Sleeping Position on the Retinal Nerve Fiber Layer in Individuals with Glaucoma. J Curr Glaucoma Pract 2024;18(2):57-62.

Stability analysis of a vertical excavation reinforced with horizontal nails using three-dimensional finite elements limit analysis

Three-dimensional stability analysis of a vertical excavation, reinforced with grouted horizontal nails, has been carried out by using the three dimensional lower and upper bounds based finite elements limit analysis (FELA) using Optum G3. The nail along with the surrounding grouted cementitious material is assumed to behave as a single monolithic cylindrical block which was assumed to be either rigid or an elasto-plastic material following the Von-Mises yield criterion. The excavation is assumed to fail on account of either an interface shear slippage between nails and surrounding soil mass or on an account of axial tensile rupture of the composite nail material for a few typical cases as well. The soil unit weight has been varied to induce the ultimate shear failure of the soil nailed excavation. The unit weight of the soil mass at which the failure of the nailed wall occurs is termed as γcr. Two different types of boundary conditions along the base of the excavation have been considered. In the first case, the in-situ soil mass behind the excavation is extended below the base as well (Case 1) and in the second case, the excavation is assumed to simply lie on a hard stratum (Case 2). The results have been provided in the form of a non-dimensional stability number N=γcrHc as a function of soil friction angle φ, Sv/H, SH/H, d/H, L/H and m; where H refers to height of the wall, d is diameter of the grouted nail, Sv and SH imply centre to centre vertical and horizontal spacing of the nails, and m is the mobilization factor between grouted nails and adjoining soil mass. The results from the analysis have been found to compare well with the data reported in literature. All the results have been presented in the form of non-dimensional stability charts, which will be useful for design for any given values of height H and cohesion c. From the observed failure mechanisms, an analysis has also been carried out to determine the optimized lengths of nails. The optimized lengths of nails for both Cases 1 and 2 have been also provided. The type of failure mechanism, base or face failure, dictates the optimized lengths of the nails.

Excavation and Construction Technology of Diversion Tunnel under Complex Geological Conditions

During the construction of a diversion tunnel, geological problems often include faults, fragile strata, hard rock formations, karst landforms, etc., which may have adverse effects on the excavation and construction of the diversion tunnel. Based on the analysis of the engineering overview, this study designed a new construction technology for the excavation of water diversion tunnels in hard rock layers and high-karst areas. Based on tunnel seismic prediction (TSP) technology to achieve advanced geological prediction, combined with actual geological conditions, construction difficulties are analyzed. Then, detection technology is used to collect two-way travel time, amplitude, and waveform data. By processing and analyzing the detection image, the spatial orientation and length of the main tunnel during the construction of the diversion tunnel are calculated. After completing the construction ventilation and wind, water, and electricity layout, the excavation construction procedure is designed. In the specific excavation design, the tunnel curtain excavation technology, tunnel body excavation and support technology, excavation grouting technology, important unfavorable geological tunnel section excavation technology, upper/lower flat section excavation technology, upper/lower curved section excavation technology, and vertical shaft section excavation technology were elaborated. Finally, a plan was made for the reuse process of slag material and a construction quality control system was established. During the testing process, it was found that the antidamage coefficient of the side wall was above 0.9 after using the technology described in this article. Therefore, it indicates that the excavation construction technology designed in this article can ensure the support capacity of the side wall of the diversion tunnel, which is suitable for the excavation of the main tunnel during the construction of the diversion tunnel.

Calculation of penetration depth of a support retaining system anchored on the top, for underground network and buried energy pipelines

AbstractThe object of the present paper is to determine the minimum support requirements provided for the safe execution of trench excavation works for underground network receptacles. This term is used to define the open excavations, which are carried out for underground networks to be installed or constructed, and which are classified in terms of place of execution and soil categories. This paper focuses on the study of the free earth support method in excavations carried out in earthy soils and in places where the passage of the pipeline requires deep excavations of vertical front. In these cases, for reasons of safety of both the personnel and the equipment, it is necessary to support the vertical excavation fronts, even when the analyses indicate their stability. In this context, and to avoid the consequences, before the start of the excavation and at its limit, the formation of vertical support structures is required, which are commonly known as "retaining bulkheads". The basic criteria for selecting the type of the support system are soil characteristics, local conditions (surface load, groundwater table) and finally, the lifetime of the trench. Based on the above, the objective of the study is to investigate the temporary support of vertical fronts of depth trenches about 10 m, the excavation of which is carried out on earthy soil. The study is based on the implementation of the limit equilibrium method, which is applied according to the provisions—guidelines set out in Eurocode 7 (EN 1997). The study investigates the distribution of earth pressures in an anchored retaining structure of a deep excavation by extracting the main design parameters of similar systems. The goal of this work is to select the type of the support system depending on the soil properties (c, γ, φ and Ε) and local conditions, as a prerequisite for safe and rational design, while in the end of the project useful conclusions are drawn.

Implementation of Surrogate Models for the Analysis of Slope Problems

Numerical modeling is increasingly used to analyze practical rock engineering problems. The geological strength index (GSI) is a critical input for many rock engineering problems. However, no available method allows the quantification of GSI input parameters, and engineers must consider a range of values. As projects progress, these ranges can be narrowed down. Machine learning (ML) algorithms have been coupled with numerical modeling to create surrogate models. The concept of surrogate models aligns well with the deductive nature of data availability in rock engineering projects. In this paper, we demonstrated the use of surrogate models to analyze two common rock slope stability problems: (1) determining the maximum stable depth of a vertical excavation and (2) determining the allowable angle of a slope with a fixed height. Compared with support vector machines and K-nearest algorithms, the random forest model performs best on a data set of 800 numerical models for the problems discussed in the paper. For all these models, regression-type models outperform classification models. Once the surrogate model is confirmed to preform accurately, instantaneous predictions of maximum excavation depth and slope angle can be achieved according to any range of input parameters. This capability is used to investigate the impact of narrowing GSI range estimation.

Settlement and bearing capacity of soil basis near vertical excavation

In the present paper, there was provided development of the method determining the statement and analytical solution of a problem which evaluates stress statement, settlement and load-bearing capacity of the weighty soil layer of limited thickness that is rested upon an incompressible soil basis and the excavation pit wall on exposure to a foundation with the distributed load in the vicinity of a wall. The analytical solution for determining the stress state component in an engineering problem is based on the Ribere-Fileon trigonometric series. Analytical solutions for determining the settlements of the soil bases based on nonlinear dependencies, taking into account the nonlinear elastic-plastic deformation properties of soils, as well as nonlinear rheological properties, are presented The obtained solutions enable to assess the deformation of soil basis and load-bearing capacity with respect to non-linear properties that accurately corresponds to the actual behaviour of soil basis under the loading. The results of stress statement were verified by numerical modelling in PC PLAXIS 2D to prove their validity and accuracy.

Long-term settlement and bearing capacity of foundations adjacent to vertical excavation at various parameters of soil viscosity

Introduction. When the underground part of a high-rise building interacts with the surrounding soil massif behind the excavation pit, a complex heterogeneous stress-strain state occurs, transforming in space and time — during construction and during the exploitation of the building. Special issues arise when the soil massif is heterogeneous and has rheological properties, and an additional load acts near the pit excavation at the same time.&#x0D; &#x0D; Materials and methods. For the problem of the stress strain statement of soil with a weight behind the enclosure of a pit with a depth h, taking into account the influence of a distributed load q = const with a width b = 2a at a distance c from the edge of the enclosing structure of the pit, the stress components were obtained using a solution based on the Ribier – Filon trigonometric series. To determine the settlement over time of the foundation near the pit, the A.Z. Ter-Martirosyan’s model was used. To describe shear deformations and the Kelvin – Foigt’s model was used to describe volume deformations, assuming that ε.z(t) = ε.v(t) + ε.γ(t), according to the Henky’s system of physical equations.&#x0D; &#x0D; Results. An analytical method has been developed for quantifying the settlement of soil bases and foundations of nearby buildings behind the pit over the time. The graphs of the settlement-time with double curvature, as well as the graph of the long-term stability of the base are obtained.&#x0D; &#x0D; Conclusions. The solutions obtained can be used to determine the long-term settlements and bearing capacity of the foundations of buildings and structures with rheological properties near the pits. The selected geomechanical model of the foundation (its geometric parameters, initial and boundary conditions), as well as the computational model of the soil (linear, nonlinear and rheological) and the type of physical equations (Hooke system or Henky system), significantly affect the type of the settlement-time curve (S–t), as well as the bearing capacity of the soils. Collaborative using of A.Z. Ter-Martirosyan’s rheological model and Kelvin – Foigt’s rheological model makes it possible to obtain settlement-time graphs with double curvature, as well as a graph of the long-term stability of the soil base.

Mathematical Computations of Long-Term Settlement and Bearing Capacity of Soil Bases and Foundations near Vertical Excavation Pits

The present paper describes and provides an analytical solution for the problem of evaluating the settlement and load-bearing capacity of weighty soil layers of limited thickness resting upon incompressible soil bases and an excavation pit wall, upon exposure of the foundation to a distributed load in the vicinity of a wall. The authors developed a method for determining the stressed state component in the reduced engineering problem based on the Ribere–Faylon trigonometric series, accounting for the nonlinear deformation properties of soils. To determine the settlement over time of the foundation near the pit, we used the A.Z. Ter-Martirosyan’s model to describe shear deformations and the Kelvin–Voigt model to describe volume deformations, assuming that ε·z(t) = ε·v(t) + ε·γ(t), according to the Hencky’s system of physical equations. The obtained solutions make it possible to assess the long-term deformation of soil bases and the long-term load-bearing capacity with respect to nonlinear rheological properties in a way that accurately corresponds to the actual performance of subsoils exposed to loading. The theoretical results were followed by numerical experiments to prove their validity.

The polygenetic floodplain of the Upper Paraná River

The mega-river functions differently from ordinary rivers and its floodplain is characterized by its magnitude, morphological complexity, and evolutionary history. This study analyzes the morphological and evolutionary characteristics of the Upper Paraná mega-river floodplain (Qm 13,000 m3 s−1), characterizing it as polygenetic owing to the various formative processes involved, many of which are no longer active and have extended since the end of the Pleistocene. The Upper Paraná floodplain is adjacent to the channel and in-channel on the large islands of its lower section. The 235 km study reach river has anabranching stretches that are separated by nodal sections. The analysis used satellite images, aerial photographs, 35 colors, and 52 absolute dates. Four types of floodplains were characterized: inherited, formed by processes and morphologies no longer active in the system; bayfill, formed by overflow deposits in flooded areas; crest-and-trough, by the annexation of lateral bars; and mixed, by the combination of the types above and association of the Paraná floodplain with its tributaries. Floodplain formation occurred in three phases. 1) At the end of the Pleistocene when the river developed a braided sand-gravel pattern under a dry climate. 2) It began at the Pleistocene-Holocene limit, when climatic improvement produced hydrological changes in the river leading to the vertical and lateral excavation of the old floodplain, generating a new channel and a sandy terrace 10 m above the current river level. The formation of the current floodplain began in this phase with the abandonment of the pioneer lake-islands. 3) It started with a small semi-arid event in the mid-Holocene until the present. The current floodplain and river hydrology were defined in this phase. Tectonic interventions for forming the floodplain are also addressed in the text. Considering its varied origin, the floodplain is polygenetic, implying a complex mosaic of environments whose connectivity relationships are still unknown. We believe that the concept of polygenetic floodplains presented in this study will help the understanding of hydrological and ecological functioning of the polygenetic floodplains of tropical mega-rivers.

Numerical investigation of the influence of banded sand ditches on water infiltration in fine-textured soil.

Enhancing rainwater infiltration is important to reduce the risk of urban waterlogging and improve the utilization rate of urban rainwater resources. Using the HYDRUS model, a mathematical model of soil water movement under a banded sand ditch pattern (the vertical excavation of a deep trench with heavy soil and filled with light soil) was created. Forty-six scenarios were designed to examine effects of sand ditch soil saturated hydraulic conductivity (Kss), original homogenous fine-textured soil saturated hydraulic conductivity (Kso), sand ditch width (W), spacing (S), and depth (D) on the soil infiltration rate (i). Results indicate that banded sand ditches cause increased permeation and have a significant turning point 't0' in the curve of 'i' for 't.' Taking 't0' as the boundary, 'i' can be divided into two stages (t ≤ t0 and t > t0), 'i' and 't,' for each stage according to the power function relationship; there is little change in power function indices, which can be fixed at 0.34 and 0.63, respectively. In addition, the coefficient has a linear relationship with Kss, Kso, W, S, and D. Thus, an estimation model of the soil infiltration rate under a banded sand ditch pattern was proposed and verified for reliability.

Settlement and bearing capacity of foundations adjacent to vertical excavation

Introduction. This article provides a solution to the problem of the settlement and bearing capacity of foundations with finite width based on rigid soil body adjacent to vertical excavation when applying a uniformly distributed load on its surface. It is assumed, that the vertical wall is fixed with sprung structures, although vertical displacement of soil is acceptable.&#x0D; &#x0D; Materials and methods. The solution of the problem was obtained by the method of trigonometric Ribere – Fileon series. Formulas for determining vertical and horizontal deformations on any coordinate x and on any horizontal (z &gt; 0) are also given. To determine the relationship between stresses and deformations, systems of Genky’s physical equations are used, which take into account the influence of σm on the shear modulus G(σm) and on the volume deformation modulus K(σm) and transform to the system of Hook’s equations at G = const and K = const.&#x0D; &#x0D; Results. The problem of the stress-strain state of a weighty layer of soil of limited capacity on a rigid soil body adjacent to vertical excavation when applying a uniformly distributed load on its surface was analytically solved. The deformations of the soil base εz were determined as the sum of shear and volumetric deformations (εz = εzγ + εzν). Based on the deformations obtained, the unevenness of the foundation settlement adjacent to vertical excavation was estimated.&#x0D; &#x0D; Conclusions. From the analysis of the results of the task, it follows that the solution of the problem of the settlement and bearing capacity of foundations with finite width based on rigid soil body adjacent to vertical excavation when applying a uniformly distributed load on its surface allows to evaluate the deformation of the foundation soils taking into account nonlinear properties. Also it provides to assess the unevenness of the sediment foundations of buildings. The further development of new methods for quantifying the stress-strain statement of soils based on known theoretical solutions is one of the main tasks of modern design of foundations and foundations of buildings and structures.

Lower bound limit analysis for an axisymmetric problem in rock mass using power cone programming

AbstractBy using the lower bound finite elements limit analysis (LB‐FELA) and the power cone programming (PCP), a methodology has been introduced to solve an axisymmetric stability problem with the usage of the generalized Hoek and Brown (GHB) yield criterion‐ applicable for rock mass. The formulation involves the application of the GHB yield criterion in its native form without any smoothing and it does not require any assumption associated with the circumferential stress (σθ). The efficacy of the proposed formulation in a rock mass has been demonstrated by determining (i) the bearing capacity of a circular footing, (ii) the stability numbers for an unsupported vertical cylindrical excavation, and (iii) the vertical uplift capacity of a circular horizontal anchor. The obtained solutions have been compared with that reported in literature. Failure patterns for each problem have also been explored. For the anchor problem, for no solution is reported with the usage of the GHB criterion, the influences of different material yield parameters (GSI, mi, and σci), unit weight of rock mass (γ), and the embedment ratio (H/B) of the anchor on the uplift capacity have been comprehensively examined.

Probabilistic stability analysis of soil nailed vertical excavation using Monte Carlo simulation (MCS)

Soil nailing is considered as one of the widely used excavation retaining systems to reinforce and strengthen the soil surface in terms of stability. It provides resistance against the deformation of the wall and improves the overall stability along the soil interface, resulting in improved performance under seismic conditions. The soil nail walls are analyzed mostly using the conventional limit equilibrium approaches. Pseudo-static and pseudo-dynamic methods consider the effect of earthquake acceleration to analyse the stability. However, these methods also had some constraint that includes the dissatisfaction of no stress boundary condition. The deterministic approach towards any earth retaining structure is not reliable and also uneconomical since it produces inaccurate results on stability analysis with a specific value as safety factor. This happens because it does not calculate the uncertainty of the influencing parameters on determining the factor of safety. As a result, in this study, the probabilistic analysis is executed to forecast the realistic failure probability of soil nailed wall. To perform probabilistic analysis, many aspects are needed for the study such as influence and effect of various parameters on achieving soil stability, and significance of safety factor in case of different modes of failure. The probability of failure (Pf) of nailed wall is estimated by Monte Carlo simulation (MCS), which is a powerful tool for stability analysis performed using the software MINITAB. This simulation method reflects realistic conditions of problem than the conventional method of stability analysis based on safety coefficients. From the results of the simulation, it is found that the probability of failure decreases with an increase in pullout capacity, axial force, and tensile capacity of the nail.

Deformation Characteristic of a Supported Deep Excavation System: A Case Study in Red Sandstone Stratum

A complete case record of a deep foundation pit with pile-anchor retaining structure excavated in red sandstone stratum is presented in this study. The horizontal displacement of pile top, the horizontal displacement at various depths, the axial force of anchor cable, and ground settlement during construction are measured. A three-dimensional numerical model is established to analyze the additional stress and deformation induced by the excavation and the accuracy of the FEM model is verified by comparing with field measured results. Both the measured and numerical simulation results show that the deformation of the pile-anchor supported deep excavation is significantly affected by the spatial effect. The results show that the deformation in the middle of the foundation pit is greater than the pit angle and that the deformation of the long side is greater than that of the short side and gradually decreases from the middle to the pit angle. The deformation and stress in the middle of the long side of the foundation pit are the largest, which is the most unfavorable part. With the increase of vertical excavation depth, the spatial effects tend to increase, and the influence scope of spatial effects is about five times the vertical excavation depth in the red sandstone stratum. The ground settlement outside the pit is mainly distributed in a groove shape, and the maximum settlement occurs about 8.5 m away from the pit edge. Finally, parametric studies of reinforcement parameters indicated that 1.5–2.0 times the initial elastic modulus and cohesive force of soil should be used for reinforcement. It is recommended that the ranges for pile diameter, pile spacing, anchor cable prestressing and inclination angle should be selected as 0.8–1.2 m, 1.4–2.0 m, 100–150 kN, and 10°–20°, respectively.