Maximum Wall Deflection Research Articles

Behaviors of Wall and Ground due to T-shaped Excavation

Extensive monitoring was performed on a T-shaped site with a length of 280 m, a width of 16 m, and a maximal depth of 20.4 m. The braced excavation was performed under retaining comprised of cast-in-situ bored piles and jet grouting piles. The field databased wall performance and its influences to ground were assessed by detailed comparisons with that in other excavations. It is showed that the wall deflections, ground movements and bracing forces all exhibited a typical camelback-shaped characteristic along the length direction, and a maximum 100% reduction of which was observed due to the jet grouting. The rebar near sections with varied excavation depths was in a tension state both on the excavation and the retained sides due to the two-dimensional unbalanced force, and the corresponding bracing force was small. The maximum wall deflection δhm decreased as the partitioning excavation moved horizontally, and it was less than 0.04% of the final horizontal excavation length Le. The normalized Fσmax approximately approached to be identical with the normalized Fbmax, while most of the occurring depths for Fσmax were greater than that for Fbmax.

Two dimensional finite element modeling of Tabriz metro underground station L2-S17 in the marly layers

Deep excavations for development of subway systems in metropolitan regions surrounded by adjacent buildings is an important geotechnical problem, especialy in Tabriz city, where is mostly composed of young alluvial soils and weak marly layers. This study analyzes the wall displacement and ground surface settlement due to deep excavation in the Tabriz marls using two dimensional finite element method. The excavation of the station L2-S17 was selected as a case study for the modelling. The excavation is supported by the concrete diaphragm wall and one row of steel struts. The analyses investigate the effects of wall stiffness and excavation width on the excavation-induced deformations. The geotechnical parameters were selected based on the results of field and laboratory tests. The results indicate that the wall deflection and ground surface settlement increase with increasing excavation depth and width. The change in maximum wall deflection and ground settlement with considerable increase in wall stiffness is marginal, however the lower wall stiffness produces the larger wall and ground displacements. The maximum wall deflections induced by the excavation with a width of 8.2 m are 102.3, 69.4 and 44.3 mm, respectively for flexible, medium and stiff walls. The ratio of maximum ground settlement to maximum lateral wall deflection approaches to 1 with increasing wall stiffness. It was found that the wall stiffness affects the settlement influence zone. An increase in the wall stiffness results in a decrease in the settlements, an extension in the settlement influence zones and occurrence of the maximum settlements at a larger distance from the wall. The maximum of settlement for the excavation with a width of 14.7 m occurred at 6.1, 9.1 and 24.2 m away from the wall, respectively, for flexible, medium and stiff walls.

Sequential Measurement and Analysis of Large Underground Retaining Structures by Diaphragm Wall Anchor for the Spring Area

The performance of a diaphragm wall‐anchor structure in spring area in Jinan city, China, is studied. Based on field measured data, lateral wall deflections, lateral soil movements, horizontal displacement of the capping beam, the maximum lateral wall deflection, ground surface settlement, lateral earth pressures on diaphragm wall, internal force of diaphragm wall, axial anchoring forces, settlements of adjacent building, and pore‐water pressure are investigated. The results indicate that the maximum deflections of the lateral wall are 0.07%∼0.18% of the excavation depth (He). The ground surface settlement influence zone extends beyond 2.5He from the pit for this project. The δv,max ranges from 0.67 δh,max to 1.0 δh,max. The maximum lateral active earth pressures on diaphragm walls above the excavation bases range between 0.4He and 0.6He. The axial anchoring forces of the top three layers of anchors change significantly during the excavation while the axial anchoring force of the fourth layer of anchor is constant. The deformation of surrounding building has three stages, including a uniform subsidence stage, an accelerated subsidence stage, and a stable subsidence stage.

Novel Excavation and Construction Method for a Deep Shaft Excavation in Ultrathick Aquifers

Dewatering using the dewatering systems composed of diaphragm walls and pumping wells is commonly adopted for deep excavations that are undertaken in deep aquifers. However, dewatering can sometimes induce environmental problems, especially when diaphragm walls cannot effectively cut off the aquifers. This paper mainly presents an innovative excavation technique combining dewatering excavation and underwater excavation without drainage, which is employed for a deep shaft excavation in ultrathick aquifers (up to 60–70 m thick aquifer) in Fuzhou, China. The shaft excavation with the depth of 41.6 m below the ground surface (BGS) is divided into two major phases, that is, (1) the first part of the excavation (the depth of 23.6 m BGS) is conducted by the way of conventional dewatering and braced excavation (Phase I) and (2) the second excavation with the depth of 23.6 m to 41.6 m BGS is carried out by the novel underwater excavation without drainage technique (Phase II). Field monitoring results show that the ratios of maximum ground surface settlement δvm to the excavation depth He in this case ranged from 0.03% to 0.1%. Most of the ratios of maximum lateral wall deflection δhm to excavation depth He are less than 0.1%. All these results are lesser than that predicted by empirical methods, which also confirmed the applicability of this innovative excavation. Thus, this innovative solution can be applicable to other deep excavations that are undertaken in ultrathick aquifers, especially for the excavation of coarse sediments with high permeability.

A Multivariate Adaptive Regression Splines model for determining horizontal wall deflection envelope for braced excavations in clays

The horizontal wall deflection of the braced excavations is influenced by many factors, including the excavation geometry, wall stiffness, soil parameters, struts spacing and so forth. In this study, three-dimensional (3D) finite element (FE) analyses were carried out to examine the corner restraining effects. A series of 3D FE analyses using the Hardening Soil (HS) model were carried out to investigate the effects of the strength of the clay, wall stiffness, excavation length, excavation depth and width, on the horizontal wall deflection envelope induced by braced-excavation in clays. Based on the results, a Multivariate Adaptive Regression Splines (MARS) model able to accurately learn the complicated implicit relationship between the maximum wall deflection envelope and these influential factors as well as the various interaction factors is developed. The developed MARS model is of good interpretability and enables the design engineer to estimate the shape of the wall deflection profiles. In addition, wall deflection profiles computed by this method compare favourably with a number of field and published records.

Plane strain evaluation of stress paths for supported excavations under lateral loading and unloading

Excavations are generally analyzed as plane strain problems. The shear strength parameters determined from the triaxial conditions are not representative of the real field conditions. Therefore, plane strain tests on reconstructed silty clay were performed using a modified apparatus to measure the stress-strain curves directly. Three stress paths were tested, where the lower shear strength and the failure strain were measured for tests with unloading in the minor principal stress direction and compared to tests with loading. A set of hyperbolic constitutive models was developed to fit the experimental data at different stress paths. The stress-strain-strength characteristics and the deformation parameters were determined for these tests. A displacement-dependent earth pressure model was then proposed for retaining walls due to excavations, and then it was calibrated against the measured soil response. In the end, a case history of bored pile walls subjected to excavations was illustrated. Calculations using the proposed approach and the standard Mohr-Coulomb model were compared. The analysis using the standard Mohr-Coulomb model was found to underestimate the maximum wall deflection by 15%.

Full-scale mechanically stabilized earth (MSE) walls under strip footing load

This study analyses two full-scale model tests on mechanically stabilized earth (MSE) walls. One test was conducted with a rigid and one with a flexible wall face. Other parameters were the same in these two tests, like the number and type of geogrid layers, the vertical distance between the layers and the soil type. The loads and strains on the reinforcement are measured as function of the horizontal and vertical earth pressure and compared with analytical models. Specifics regarding the behavior of the geogrids under the compaction load during the construction of the model and under strip footing load are included in the study. Results are compared with AASHTO and the empirical K-stiffness method. In this study, an analytical method is developed for the MSE walls taking into account the facing panel rigidity both after backfill construction and after strip footing load. There is good agreement between the proposed analytical method and the experimental results considering the facing panel rigidity. The results indicate that the tensile force on reinforcement layers for rigid facing is less than the flexible facing. The maximum strains in the reinforcement layers occurred in the upper layers right below the strip footing load. The maximum wall deflection for the flexible facing is more than for the rigid facing. The maximum deflection was at the top of the wall for the rigid facing and occurred at z/H = 0.81 from top of the wall for the flexible facing.

A multivariate adaptive regression splines model for estimation of maximum wall deflections induced by braced excavation

With rapid economic growth, numerous deep excavation projects for high-rise buildings and subway transportation networks have been constructed in the past two decades. Deep excavations particularly in thick deposits of soft clay may cause excessive ground movements and thus result in potential damage to adjacent buildings and supporting utilities. Extensive plane strain finite element analyses considering small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by diaphragm walls and bracings. The excavation geometrical parameters, soil strength and stiffness properties, soil unit weight, the strut stiffness and wall stiffness were varied to study the wall deflection behaviour. Based on these results, a multivariate adaptive regression splines model was developed for estimating the maximum wall deflection. Parametric analyses were also performed to investigate the influence of the various design variables on wall deflections.

A new measurement approach for deflection monitoring of large-scale bored piles using distributed fiber sensing technology

A novel distributed fiber optic strain sensing technology, named Brillouin optical time-domain analysis (BOTDA), has been used to study the performance of large-diameter bored piles subjected to a slope excavation in Hong Kong. A new installation method for the distributed fiber optic sensors (FOS) in the bored piles was proposed in this study. Distributed strains along the instrumented bored piles were obtained by BOTDA sensors during multi-stage excavations. Details of sensor design, field installations, sensor protections, and data analysis are presented in this paper. Axial and bending strains along the instrumented pile were obtained by two sets of BOTDA sensors installed on diametrical opposite sides along the pile. The calculation method for deriving the lateral deflections from distributed strains is described. Thus, the calculated lateral deflections from BOTDA sensors were compared with the traditional inclinometers which were installed at the center of the same instrumented bored pile. Measurements obtained from the BOTDA sensors were found to be in good agreement with the inclinometer data. The maximum lateral wall deflection over the excavation depth was between 0.05% and 0.1%. The lessons learned from this field implementation are discussed and suggestions provided for further similar applications. Field application in this study reveals that the BOTDA measurement has great potential to be used for performance monitoring of large diameter piles.

Multivariate Adaptive Regression Splines Approach to Estimate Lateral Wall Deflection Profiles Caused by Braced Excavations in Clays

Based on a database including a total of 30 case histories for braced excavation in stiff, medium and soft clays, a multivariate adaptive regression splines (MARS) approach for estimating wall deflection profile caused by deep braced excavations is presented in this study. For each soil type, ten case histories with information on subsurface soil conditions, geometry characteristics, excavation support system details, the maximum wall deflections and the wall deflection profile against embedded depth are provided. Seven input variables, including wall length, excavation depth, excavation length, system stiffness, average unit weight and undrained shear strength of the soil, and the depth below the ground surface, are adopted as inputs to the MARS deflection profile model. Comparison with three more excavation case histories indicates that the developed MARS model can give an accurate graphical representation of the wall deflection profile. It is capable of not only predicting the value of maximum wall deflection but also estimating the possible depth at which maximum lateral deformation occurs.

Wall and Ground Movements due to Deep Excavation of Tianjin Subway Station

This paper analyzes wall deflection and ground surface settlement due to deep excavation. 21 case histories of Tianjin subway line 6 are collected and analyzed. And the results are compared with previous field studies worldwide. The mean value of maximum wall deflection δhm is 0.11%H, in which H is the excavation depth. The upper limit of δhm is 0.44%H when H is less than 8m and 35mm when H is more than 8m. When excavation finished, δhm ranges from 0.02%H to 0.24%H with an average value of 0.12%H. The depth of maximum wall deflections Hδhm is within 0.75H±8m and the average Hδhm is 0.69H when excavation finished. It’s greatly affected by the embedded depth ratio. Hδhm can be predicted by exponential function more accurately. The distribution of δvm generally extends to a distance of 2H from the diaphragm wall. The bound of stiff clay line proposed by Clough and O’Rourke (1990) and bilinear curve proposed by Erin H. Y. Leung (2007) can be used as the upper bound for ground surface settlement for excavation of Tianjin subway line 6. The ratio between δvm and δhm generally ranges from 0.34 to 2.66, with an average value of 1.13. It’s consistent with the average value of 1.21 collected from literature in similar soil conditions. This paper is a reference for design and construction of Tianjin’s deep excavation of subway station.

A simple estimation model for 3D braced excavation wall deflection

A series of two-dimensional (2D) and three-dimensional (3D) finite element analyses using the Hardening Soil (HS) model were carried out to investigate the influences of soil properties, wall stiffness, excavation length, excavation depth, clay thickness at the base of the excavation and wall embedment depth, on the maximum wall deflection induced by braced-excavation. The results show that the 3D maximum wall deflections are generally much smaller than those for 2D. Comparisons were also made with other commonly used semi-empirical charts. Based on the finite element results in this study, a simple wall deflection equation was developed for estimating the maximum wall deflection that takes the 3D effects into consideration through different ratios of excavation length over excavation width.

Probabilistic analysis of responses of cantilever wall-supported excavations in sands considering vertical spatial variability

The influence of vertical spatial variability of sands on the excavation-induced lateral wall deflection and bending moment of excavations supported by cantilever retaining walls is investigated in this paper. Herein, the random finite element method (RFEM) is adopted to explicitly study the effect of one-dimensional spatial variability of internal friction angle of sands on the predicted wall and ground responses. The RFEM analysis consists of three components: (1) finite element method for analyzing lateral wall deflection and bending moment, (2) random field theory implemented with Monte Carlo simulation (MCS), and (3) statistical interpretation of MCS results through confidence intervals. This study reveals the importance of random field modeling in coping with the spatial variability of sands in the problem of supported excavations: (1) neglecting spatial variability of soil property will cause an overestimation of the variation in the predicted wall deflection and bending moment; (2) the estimated probability of failure based on a well-established serviceability limit state may be overestimated or underestimated depending on the chosen limiting lateral wall deflection. This study further investigates the effect of the number of MCS on the confidence intervals of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment. The results also demonstrate that the confidence interval analysis of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment provides a rational tool for interpreting the statistical data from RFEM.

Three-dimensional effects on deformation of deep excavations

To research the influence of three-dimensional (3D) effects on the deformation of deep excavations, a database of 30 deep excavations of Nanjing metro stations in China was analysed and comparisons with worldwide cases were conducted. It was found that maximum wall deflections in zones influenced by 3D effects are generally less than those in zones not influenced by 3D effects, while the normalised locations of maximum wall deflections are the same in the two zones. The ratios of maximum wall deflection to excavation depth in zones influenced by 3D effects was found to be generally less than those in zones not influenced by 3D effects. 3D effects were also found to influence ground settlement. Three settlement models – for zones not influenced by 3D effects, zones influenced by 3D effects and zones of soil arch springs – are proposed and comparisons are made. The ratio of maximum ground settlement to excavation depth was found to be 0·12% on average and the ratio of maximum ground settlement to maximum wall deflection was 0·64 on average. The findings of this research can be applied to predict deformation and protect surrounding buildings.

Updating Soil Parameters Using Spreadsheet Method for Predicting Wall Deflections in Braced Excavations

A back analysis procedure implemented in a spreadsheet environment that uses construction monitoring data for supported excavation systems to continuously recalibrate the soil parameters and thus enable updating of the lateral wall deflection predictions is presented. With this framework, the observed maximum wall deflections are used to update the soil parameters through a recently developed semi-empirical polynomial regression model. This paper demonstrates that the updated soil parameters recalibrated from the current stage of excavation can be used to predict the maximum wall deflection in the subsequent stages of excavation. The proposed framework is computationally efficient and can easily be implemented in a spreadsheet. The feasibility and effectiveness of the proposed methodology is illustrated through seven well-documented excavation case histories. The results of the case histories show that the updated soil parameters improve the accuracy of estimations of the wall deflections in braced excavations.

Interaction between a large-scale triangular excavation and adjacent structures in Shanghai soft clay

Despite much attention being paid to the performance of rectangular basement excavation, the deformation characteristics of triangular excavations and their effects on nearby structures are not fully studied. A large-scale triangular basement with a final excavation depth of 22.8m excavated at two sides of a cut-and-cover tunnel was extensively instrumented in Shanghai soft clay. Differing from the wall deflection in rectangular excavations, the lateral movements at the top of retaining walls in a triangular excavation was up to 70% of the maximum wall defection even though the first concrete props were cast before commencement of the main excavation. Upon completion of the base slabs, the maximum lateral wall deflection (δhm) ranged from 0.05% H to 0.35% H (excavation depth). During subsequent construction of remaining concrete slabs, δhm increased by up to 50%. Prior to completion of the base slabs, heaves were induced in interior column and diaphragm wall resulting from excavation-induced stress relief. Measured maximum heaves in the interior column and diaphragm wall were 0.08% H and 0.06% H, respectively. Different deformation mechanisms were observed in the cut-and-cover tunnel and shield tunnel. Heave was induced in the cut-and-cover tunnel located within excavation zone with a maximum value of 7.9mm. On the contrary, settlement was observed in the shield tunnel located outside of excavation zone with a maximum value of 8.0mm. Because of corner effects in basement excavation, three-dimensional deformation mechanisms were observed in the existing pipelines running parallel and behind the retaining walls. Due to post-excavation wall deflection induced ground settlement, the incremental maximum pipeline settlement was up to 120% of that upon completion of the base slabs.

Probabilistic Assessment of Serviceability Limit State of Diaphragm Walls for Braced Excavation in Clays

AbstractBraced excavation systems are commonly required to ensure stability in the construction of basements for shopping malls and underground transportation facilities. For excavations in deposits of soft clays, stiff retaining wall systems such as diaphragm walls help to restrain ground movements and wall deflections in order to prevent damage to nearby buildings and utilities. It is quite common for designers to limit the maximum wall deflection to 0.5% times the maximum excavation depth. However, a review of measured diaphragm wall displacements from various published case histories of successful deep excavations show that wall deflections can be up to more than 2% times the excavation depth. Since the allowable threshold wall displacement depends on various influencing parameters, wall deflections should not be limited to an arbitrary value. This paper presents a probabilistic framework combining a simplified wall deflection estimation model with reliability methods to determine the probability of s...

Simplified approach to estimate the maximum wall deflection for deep excavations with cross walls in clay under the undrained condition

Previous studies have shown that use of cross walls in deep excavations can reduce the wall deflection to a very small amount. However, design of cross walls is costly because the deflection behavior of the diaphragm wall with cross walls is in nature three dimensional. The objective of this study was to establish a simplified approach used as a first approximation to design cross walls such that the lateral wall deflection can satisfy a design criterion. A series of parametric studies using a three-dimensional numerical method was performed to obtain the influence factors on wall deflections, including excavation geometry, wall system stiffness, axial stiffness of strut, axial stiffness of the cross wall, normalized undrained shear strength of clay and the cross wall depth. Then, a simplified formula for predicting the wall deflection for excavations without and with cross walls was established using multivariate regression analysis, respectively. The formulas were validated through 36 excavation cases without cross walls and 12 cases with cross walls. The simplified formulas can be used to develop a spreadsheet that estimates the cross wall sizes and intervals based on the entered excavation geometry, material properties of retaining-strut system, in situ undrained shear strength and tolerable wall deflection. The estimated cross wall sizes and intervals should be verified by an appropriate full numerical analysis.

A simple prediction model for wall deflection caused by braced excavation in clays

Deep excavations particularly in deep deposits of soft clay can cause excessive ground movements and result in damage to adjacent buildings. Extensive plane strain finite element analyses considering the small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by retaining walls and bracing. The excavation geometry, soil strength and stiffness properties, and the wall stiffness were varied to study the wall deflection behavior. Based on these results, a simple Polynomial Regression (PR) model was developed for estimating the maximum wall deflection. Wall deflections computed by this method compare favorably with a number of field and published records.

Evaluation of wall deflections and ground surface settlements in deep excavations

A study to illustrate the ground surface and wall movements due to excavation is undertaken based on two-dimensional nonlinear finite element (FE) modeling and analysis. The FE model and nonlinear solution strategy are built in the open-source software platform, OpenSees, of the Pacific Earthquake Engineering Research Center. A drained analysis was carried out using Drucker–Prager multisurface kinematic plasticity model for sand. The proposed model is verified using a case history in an urban excavation. The ground surface settlement and wall deflection for the various conditions of excavation are calculated. The results indicate that the extent of the settlement zone depends on excavation depth and is predicted as 2.5–3 times excavation depth, and the upper limit of the maximum ground surface settlement is equal to the maximum lateral wall deflection.