Maximum Lateral Wall Deflection Research Articles

Mechanical responses of shallowly buried pipelines to adjacent deep excavations considering heavy rainfall influence

Climate change has resulted in a high global incidence of heavy rainfall, severely damaging the urban infrastructure. The analytical method used to predict the mechanical response of pipelines under the influence of rainfall influence could serve as a valuable design basis in the preliminary stage. This study developed an analytical solution based on the stratified Green-Ampt model and displacement-controlled two-stage method. The first stage evaluates the greenfield soil displacement at pipeline elevation by employing the Mindlin solution and considering the superposed effects of excavation (unloading) and rainfall infiltration. The second stage predicts the mechanical responses of the pipeline by simplifying the pipeline–soil interaction into a continuous Euler–Bernoulli beam resting on a Winkler foundation model. The analytical solution was calculated using the finite difference method and verified against a published study. Finally, parametric studies were conducted to investigate the rainfall– excavation–pipeline interaction, including the rainfall intensity and duration, maximum lateral wall deflection, and pipeline location. The results showed that a 48-8-mm/h rainfall increased the maximum displacement and maximum bending moment of the pipeline by 6.54% and 7.93%, respectively. The prediction results provide practical guidance for designing deep excavations adjacent to pipelines buried under heavy rainfall conditions.

State-of-the-art review of soft computing applications in underground excavations

Soft computing techniques are becoming even more popular and particularly amenable to model the complex behaviors of most geotechnical engineering systems since they have demonstrated superior predictive capacity, compared to the traditional methods. This paper presents an overview of some soft computing techniques as well as their applications in underground excavations. A case study is adopted to compare the predictive performances of soft computing techniques including eXtreme Gradient Boosting (XGBoost), Multivariate Adaptive Regression Splines (MARS), Artificial Neural Networks (ANN), and Support Vector Machine (SVM) in estimating the maximum lateral wall deflection induced by braced excavation. This study also discusses the merits and the limitations of some soft computing techniques, compared with the conventional approaches available.

Deformation Characteristics of Retaining Structures and Nearby Buildings for Different Propped Retaining Walls in Soft Soil

Abstract This article reports the field performance of deep excavations of two subway station cases, including the lateral wall deflection behavior and settlement trends of the surrounding soil and nearby buildings. The retaining structures employed in these cases were contiguous pile walls (CPW), soil-mixing walls, and diaphragm walls (DW), all of which were embedded in soft clay. The measured wall deflection profiles exhibited typical bulging behavior at the end of the excavation. The ratios of the measured maximum wall deflection to the excavation depth were found to be similar for all three types of retaining wall. Furthermore, the maximum and minimum corner effects on the wall deflection development were obtained for the DW and CPW, respectively. The measured ground surface settlement increased linearly with increased maximum lateral wall deflection, while the settlement magnitude became extraordinarily large because of the presence of sludgy soil. A concave pattern was proposed for the surface settlement profiles for all three types of retaining wall. The building settlement was quantified, with the value lying between those of the surface settlement and soil settlement at 10-m depth. The soil displacement field induced changes in the side and end resistance behaviors of the loaded piles, along with additional settlement of pile-foundation buildings. In addition, the pile-foundation building settlement was influenced by the corner effect. These research results will enhance our understanding of the deformation characteristics of the retaining structure and nearby buildings. Meanwhile, the findings will provide guidance for the optimal design of the retaining structure in soft soil.

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.

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.

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 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.

Performance of a Deep Excavation and Its Effect on Adjacent Tunnels in Shanghai Soft Clay

AbstractA 267-m-long, 54-m-wide, and 14.9–16.4-m-deep multipropped deep excavation with three cross walls in Shanghai soft clay was constructed at a side of an existing metro station. To investigate the performance of this deep excavation and the effect of this deep excavation on adjacent metro station and shield tunnels, the ground deformation and structure responses were extensively monitored. Based on the field observations, the deflections and vertical movements of diaphragm walls, surface settlements, vertical and horizontal displacements of the up track and the down track within the station and nearby shield tunnels, as well as tunnel convergence were extensively analyzed. By adopting cross walls, jet grouting and large dimension concrete struts, the measured maximum lateral wall deflection and ground deformation were much smaller than those at other sites without installing cross walls in Shanghai soft clay. The maximum excavation-induced lateral wall movements and ground settlement behind the reta...

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.

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.

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.

Comparison of excavation-induced wall deflection using top-down and bottom-up construction methods in Taipei silty clay

This paper compares the excavation-induced wall deflection caused by the top-down method (TDM) and the bottom-up method (BUM). First, a total of 26 quality excavation case histories in Taipei silty clay were collected and analyzed. The field observations show that the maximum lateral wall deflection ( δ hm) induced by the TDM were 1.28 times as large as that induced by the BUM. Factors affecting wall deflection are investigated and four of them are selected for further numerical experimentation to investigate the discrepancy of δ hm caused by the two methods. Analysis results showed that the average ratio of δ hm induced by the TDM over that induced by the BUM is approximately equal to 1.1, excluding the effect of thermal shrinkage of concrete floor slabs. Both observed data and analysis results revealed that greater δ hm is generally induced by the TDM despite its use of floor slabs with higher support stiffness.

Displacement Flexibility Number for Multipropped Retaining Wall Design

The results from 30 nonlinear finite-element analyses of undrained deep excavation in stiff clay are used to support the use of a new displacement flexibility number in multipropped retaining wall design. The analyses address the effects of different initial stress regimes and various values of prop stiffness for the internal supports to the excavation. It is demonstrated that this flexibility number defines support systems that will displace to the same maximum lateral wall deflection and will result in the same profiles of vertical and horizontal ground surface displacement behind the wall. It is concluded that, as it is these movements that must be controlled to limit the damage to adjacent buildings, structures, and services, the new flexibility number gives the engineer more confidence in assessing possible support strategies to a given problem at a given site.

Characteristics of ground surface settlement during excavation

The objective of this paper is to study the characteristics of ground surface settlement during excavation. Ten excavation cases in Taipei with good-quality construction and field observation data are selected to study the characteristics of excavation behavior. The location of maximum lateral wall deflection, magnitude of maximum lateral wall deflection, relationship of maximum lateral wall deflection and maximum ground surface settlement, location of maximum ground surface settlement, and apparent influence range are thus established based on the actual excavation cases. Finally, an empirical formula is proposed to predict the ground surface settlement profile at the center section of an excavation, where the behavior may be characterized by plane-strain conditions. Key words : excavation, surfac settlement, wall deflection, plane strain, empirical formula.