Excavation-induced Ground Movements Research Articles

Effect of Wall Stiffness on Excavation-Induced Horizontal Deformations in Stiff-Hard Clays

Excavation-induced ground movements are affected by the stiffness of the support system as well as the soil properties. Displacement estimations of deep excavations are generally made using the finite element method (FEM). However, the accuracy and reliability of the results obtained from the finite element calculations will change significantly in proportion with the quality of the parameters employed in the program, thus, the use of probabilistic analysis that considers soil variability’s impact has become a popular approach in recent studies. Based on these considerations, this study aims to investigate the influence of wall bending stiffness on excavation-induced lateral displacements for deep excavations in stiff to hard clays, and provide a practical methodology to be used in preliminary design. For this purpose, finite element analyses were carried out using various practically achievable support system stiffness values and soil parameters. Considering the inherent variability of the soil, effective stress friction angle and effective cohesion of the soil were randomly generated by Monte Carlo simulations to be used in the finite element analyses. The performance of the analyses was evaluated using results from 22 case histories from deep excavations in stiff-hard clays. The results indicate that, lateral movement in excavations in stiff-hard clays is minimally affected by the stiffness of the wall. Soil variability was found to have a significant impact on the outcome of Monte Carlo simulations, resulting in a wide range of normalized maximum lateral deformations for a given wall stiffness. A new stiffness factor has been proposed that incorporates the horizontal spacing of the support elements, which is capable of covering a wider range of excavation support system types, thus enhancing the accuracy of the analyses.

Method for Estimating Fully Coupled Response of Deep Excavations in Soft Clays

The influence of excavation rate, geometric layout, and hydraulic conductivity of basal and retained soils on the fully coupled solid–fluid behavior of braced excavations in cohesive soils is presented. Fully coupled excavation analyses were performed using the hypoplasticity clay model to reproduce the constitutive soil behavior combined with Biot’s consolidation theory. A method aimed at predicting excavation-induced ground movements using excess pore-water pressure ratios as a function of site-specific groundwater considerations is presented for the determination of the recommended type of excavation analysis (i.e., drained, partially drained, or undrained). Results obtained from the numerical simulations indicated that excavation rate to hydraulic conductivity ratios, ER/k, smaller than 0.1 and larger than 10,000 can be analyzed under drained and undrained conditions, respectively. The proposed method was validated with published case histories, and its ability to estimate excavation performance in terms of excess pore-water pressures and excavation rates is presented in this paper.

Building Response to Excavation-Induced Ground Movements from a Nonlinear-Inelastic Perspective

The nonlinear-inelastic response of reinforced concrete moment-resisting frame buildings due to an adjacent excavation in soft to medium clays is presented. An advanced numerical model is used to account for building-soil-excavation interactions, post-yielding behavior of the structural members, and solid-fluid coupled behavior of supporting soils. The effects of the excavation on the internal force redistributions of structural members, lateral and vertical distortions, ground surface settlements, and lateral wall movements are presented in terms of angular distortions and drifts, curvature ductility, axial forces, and flexural moments. Results showed how beams progressively developed plastic deformations as deep-seated movements occurred during the excavation of soft and medium clays, reaching maximum curvature ductility ratios larger than 2. As the excavation advanced, maximum curvature ductilities of up to 5 were computed in beams closer to the excavation, causing localized inelastic mechanisms in the building. This paper shows how even well-designed buildings to withstand large levels of lateral load demands using strong column–weak beam approaches can still be subjected to significant excavation-induced nonlinear-inelastic demands that can cause damage.

Predicting longitudinal tunnel deformation due to deep excavation-induced ground movement

Many excavations in urban areas are carried out near existing subway tunnels. To protect the tunnels, it is important to predict the longitudinal tunnel deformation induced by the soil movement caused by excavation. A three-stage method is proposed in this paper. In the first stage, a dual-spring Winkler model is proposed to calculate the lateral deflection of the retaining wall by explicitly accounting for the small-strain behavior of soils. In the second stage, the three-dimensional free-field soil movement induced by braced excavation is calculated by an analytical model that considers the lateral deflection of the retaining wall as the only input. In the third stage, the response of the tunnel is evaluated by simplifying the tunnel as an elastic foundation beam on Winkler springs and subjecting it to the soil movement computed in the previous stage. The validity and accuracy of each stage in this method are examined with finite element simulation results and field observations. Finally, parametric studies are also performed to investigate the effects of the small-strain behavior of the soil, the parameters of the retaining system, and the tunnel depth on the susceptibility of tunnels to deep excavation-induced ground movement.

Performance of inclined-vertical framed retaining wall for excavation in clay

A new strut-free retaining wall system, referred to as an inclined-vertical framed retaining wall (IVFRW), is constructed for excavation in clay. It has been successfully used in engineering practice to limit excavation-induced ground movement and protect adjacent buildings. This paper presents the performance of an excavation constructed by using IVFRW in Tianjin, China. Field investigations indicate that the proposed retaining structures effectively limit the wall deflection. Parametric studies based on the validated three-dimensional finite element model are conducted to improve the fundamental understanding of the mechanism of IVFRW. The influence of the inclined pile and vertical pile lengths on the deformation, internal forces, and wall friction are studied. A concept of neutral plane in retaining wall is proposed, and the mobilization of the skin friction and the axial force linking with earth pressure are analysed. Finally, a design concept for IVFRW is discussed.

Performance monitoring of a curved shield tunnel during adjacent excavations using a fiber optic nervous sensing system

With the accelerated urbanization and population growth in the Yangtze River Delta of China, numerous metro tunnels are in operation or under construction, and adjacent deep excavation activities are frequently encountered. For curved shield tunnels, the impact of excavation-induced ground movements is more complicated due to their asymmetric shape. This paper presents the monitoring results of a curved shield tunnel in clayey soil in Suzhou, China, which were captured by a fiber optic nervous sensing system. This system utilized Brillouin optical frequency domain analysis technology to monitor the distribution of longitudinal and circumferential strains of tunnel linings induced by adjacent excavation. The results show that the tunnel linings were mainly subjected to bending deformations along the tunnel alignment. Maximum compressive strains were observed below the tunnel springline, and their absolute values were higher than those of maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into a rotated oval/ellipsoid. Based on the monitoring results, two kinematic models reflecting the spatial relationship between movements of tunnel segments and measurements of strain sensing cables are proposed. Furthermore, a mechanical method is proposed to convert strain measurements into radial displacements of tunnel linings and the structural health condition of the tunnel is evaluated using longitudinal and circumferential risk indexes. The conclusions drawn in this study provide improved insight into the deformation pattern and health condition of curved shield tunnels subjected to adjacent excavations.

Construction-induced effects in a cofferdam excavation using Hypoplasticity and Shotcrete models

Construction-induced effects of concrete bracings on excavation-induced ground movements in an urban cofferdam are investigated using advanced constitutive models. Hypoplasticity model for clays and Shotcrete model for concrete were used to reproduce the performance of a bottom-up cofferdam excavation braced with seven levels of concrete ring beams. Construction effects associated with rapid cycles of soil removal and lateral bracing, low temperatures during concrete curing and installation, and concrete time-dependent effects (i.e., shrinkage, creep, and aging) are studied parametrically in terms of excavation-induced lateral wall movements. The computed results from the numerical simulations matched well field performance measurements. Concrete material time-dependent effects represented approximately 30% of the maximum lateral wall movements; aging was the predominant effect. Concrete curing and ring beam installation effects represented 25% of the computed maximum lateral wall deformations. Excavation designs ignoring the proposed effects would potentially cause damage to nearby infrastructure.

Observed performance of a deep excavation of Qingdao Metro Line 4 in China

The L-shaped excavation of Anshan Road Station, with the maximum excavation depth of about 40 m, is one of the deepest excavations of Qingdao Metro Lines in Qingdao, Shandong Province, China. The deep excavation was constructed mainly in coarse-grained granite of different weathering degrees. A comprehensive field monitoring scheme was carried out to study excavation-induced ground movement and the response of nearby structures. Characteristics of ground surface settlement and pier settlement of Hang’an Expressway Viaduct adjacent to sub-zone D of the L-shaped excavation was studied based on the long-term monitoring data. A high-risk zone of rock failure at sub-zone D was successfully identified based on abnormal variations in the horizontal displacement of pile head and axial force of cable, concentration of microseismic events, and development of a 44-m-long longitudinal crack adjacent to the excavation boundary. A temporary bracing system, consists of two layers of steel struts and built-up steel columns, was designed and conducted to maintain the stability of the high-risk zone of rock failure at sub-zone D. Furthermore, effectiveness of the temporary bracing system in controlling rock failure of the L-shaped excavation was validated by analyzing the evolution of the axial force of steel struts, horizontal displacement of pile head and axial force of cable. This study may be valuable for monitoring, warning and controlling rock failure of deep excavations in hard rocks in dense and busy urban areas.

Damage Estimation in Masonry Buildings Based on Excavation-Induced Ground Movements

Excavation-induced ground movements and the resulting damages to adjacent structures and facilities is a source of concern for excavation projects in urban areas. The concern will be even higher if the adjacent structure is old or has low strength parameters like masonry building. Frame distortion and crack generation are predictors of building damage resulted from excavation-induced ground movements, which pose challenges to projects involving excavations. This study is aimed to investigate the relation between excavation-induced ground movements and damage probability of buildings in excavation affected distance. The main focus of this paper is on masonry buildings and excavations stabilized using soil nail wall method. To achieve this purpose, 21 masonry buildings adjacent to 12 excavation projects were studied. Parametric studies were performed by developing 3D FE models of brick walls and excavations stabilized using soil nail wall. Finally, probability evaluations were conducted to analyze the outputs obtained from case studies. Based on the obtained results, simple charts were established to estimate the damage of masonry structures in excavation affected distance with two key parameters including “Displacement Ratio” and “Normalized Distance”. The results also highlight the effects of building distance from excavation wall on its damage probability.

The Effects of Multipropped Deep Excavation-Induced Ground Movements on Adjacent High-Rise Building Founded on Piled Raft in Sand

In this paper, a three-dimensional numerical parametric study was conducted to predict the deformation mechanism of a 20-storey building sitting on a (4 × 4) piled raft to an adjacent 25 m deep basement excavation. The influences of different excavation depths were investigated. An advanced hypoplastic sand model (which is capable of taking small-strain stiffness into account) was adopted to capture soil behaviour. The computed results revealed that excavation adjacent to a building resting on the piled raft caused significant settlement, differential settlement, lateral deflection, and interstorey drift in the building. With settlement due to working load (i.e., 4.8dp%), the total settlements of the building (7.8dp%) exceed the maximum allowable foundation settlement (i.e., 50 mm). In addition, substantial bending moment, shear forces, and changes in axial load distribution along pile length were induced. The findings from this study revealed that the building and pile responses are significantly influenced by the excavation depth.

A simplified estimation of excavation-induced ground movements for adjacent building damage potential assessment

Adjacent building damages induced by excavations is crucial for excavations in urban areas. Excavation induced damage involved complex soil-structure interactions and complicated ground movements which should be evaluated at the depth of foundation of adjacent buildings. Empirical or semi-empirical methods for evaluation of ground movements induced by excavations have not been well-established because the observed ground movements are very limited. The objective of this study is to establish a simplified assessment for building damage potential based on subsurface ground movements caused by excavations. A series of parametric study by numerical analyses with an advanced soil model was carried out. A set of simplified equations for predicting the profiles for both subsurface ground settlements and lateral ground movements were proposed. Three assessment models with or without considering structural stiffness and subsurface ground movements were employed in estimating the damage potential index (DPI) for two case histories. The models were proved to yield a more reasonable assessment result for building DPI based on the proposed simplified expression of subsurface ground movements.

Estimation of building damage in a 3D distorting structure to tunnel and underground excavation-induced ground movements

Estimating building damage due to ground movements induced by tunneling or open cutting is very important for planning, design, and construction. Such efforts can minimize any possible damage in adjacent structures and help in choosing the most efficient protection measures if needed. This study extends a damage estimation criterion based on the 2D state of strain (Son and Cording, 2005) to estimate building damage and distortion in 3D structural distortion conditions. The 3D state-of-strain concept is used to develop a damage criterion that can be used to estimate building damage and distortion in 3D distorting structural units. The extended 3D criterion is compared with observed field observations as well as numerical test results. The study results can provide a better understanding of building damage estimation in 3D structural distortion conditions in response to tunnel and underground excavation-induced ground movements.

Crack Pattern Investigation in the Structural Members of a Framed Two-Floor Building due to Excavation-Induced Ground Movement

Increased urbanization causes traffic and parking issues especially in metropolitan cities like Karachi, London, Shanghai, etc. To accommodate parking issues for the vehicles mainly in urban areas (excavated) underground parking areas under or nearby high rise buildings are preferred. As a result of excavation, ground movements occur that have a major impact on structures, buildings, and utilities. The past research usually oversimplified surface structure as an equivalent elastic beam, which is unable to represent the behavior of a framed building realistically. In this study, the detrimental effects (i.e. crack pattern) on a two-floor RCC framed building founded on piles due to an adjacent excavation-induced ground movement are investigated. Elasto-plastic coupled-consolidation analysis was adopted. The hypoplastic constitutive model was used to capture soil behavior. It is an advanced model which is able to capture the soil unique features which are non-linear behavior, stiffness degradation (with stress, strain & path-dependent), and stress-strain dependent soil dilatancy. The concrete damaged plasticity (CDP) model was used to capture the cracking behavior in the concrete beams, columns and piles. It was revealed that the induced slope and tilting are not equal. Consequently, the frame was distorted. As a result, tension cracks were induced at the inner side of the column.

Numerical Simulation of Recent Stress-History Effects on Excavation Responses in Soft Clays

AbstractA finite element analysis of a hypothetical excavation was conducted to investigate recent stress-history effects on excavation-induced ground movements. The numerical simulations were cond...

Single Pile Settlement and Load Transfer Mechanism due to Excavation in Silty Clay

In densely built areas, development of underground transportation system often involves excavations for basement construction and cut-and-cover tunnels which are sometimes inevitable to be constructed adjacent to existing piled foundations. In order to gain new insights into single pile responses (i.e. settlement and load transfer mechanism) to an adjacent excavation in saturated silty clay, a three-dimensional coupled- consolidation numerical analysis is conducted in this study. An advanced hypoplasticity (clay) constitutive model with small-strain stiffness was adopted. A linear increase in pile settlement was observed due to excavation-induced stress release. This is because part of the pile is placed within the boundaries of a major influence zone due to excavation-induced ground movement. Based on a settlement criterion, apparent loss of pile‘s capacity is 14%. A maximum bending moment of about 350 kNm is induced in the pile with the maximum deflection of 28 mm. In addition, mobilisation of shear strength at the pile-soil interface was found to be a key factor governing pile-soil-excavation interaction. During excavation, a downward load-transfer mechanism in the piles can be identified.

Building response to tunnelling- and excavation-induced ground movements: using transfer functions to review the limiting tensile strain method

In this paper, limiting tensile strain method (LTSM) is reviewed, and advantages and disadvantages resulted from the simplicity of this method are examined in the light of the findings of the existing experimental and numerical studies. Using the viewpoint of the transfer functions for the LTSM, a more independent sight for the interpretation of the relationships between deflection ratio, structure’s geometry, longitudinal/shear stiffness ratio and the limiting tensile strain is provided. In addition, the effect of average horizontal strain is included simply in the modified deep beam equations. Using reported data and observed damage classes of real and simulated case studies available in the literature, back-calculations for the coefficients of the transfer function are made. After comparing the back-calculated coefficients to the original coefficients of the LTSM, it is shown that observed damage and measured crack widths are reasonably compatible with the proposed limiting tensile strain boundaries. Also, it is shown that for the cases in which moderate or higher damage was observed, the original deep beam equations tend to underestimate the resultant damage.

Effect of structural features in a distorting structure due to excavation-induced ground movements

This study examined the effects of structural features in a distorting structure due to excavation-induced ground movements numerically based on the justifiable comparison between a physical model test and its numerical simulation. For examining the effects of structural features this study focused on the effect of roof restraint, the effect of window opening, and the effect of grade beam on structure distortion and cracking. In this study the considered structure was block-bearing structures, in which cracking can easily be formed along block joints so that the structural response can be directly compared each other. The 2-D Universal Distinct Element Code (UDEC 3.1) was used to model the structures and examine the responses of structures. The results of numerical studies indicated that the structural features affected a structural response considerably, and therefore for more reliable assessment of the response of structures subjected to excavation-induced ground movements the effects of structural feature should be carefully evaluated and considered.

Excavation-Induced Settlement and Tilt of a 3-Story Building

AbstractA 3-story building was found tilted badly as a result of a nearby deep excavation. Numerous cracks were developed on the facade walls and load-bearing brick walls. Dislodgement of some timber joists was observed at some parts of the second and third stories of the building. A detailed assessment of the conditions of the building was carried out. Unlike current prevailing practice, the assessment of damages caused by excavation-induced ground movements of this building includes tilts and out-of-plumbs of the load-bearing brick walls. The present study proposes to assume that the building behaves as a rigid body, and with appropriate empirical building correction factors to correct the inappropriateness of this assumption, reasonable estimates of the resulting out-of-plumbs of load-bearing brick walls of such buildings caused by a nearby deep excavation can be obtained. The empirically derived building correction factor is validated by comparing the predicted and measured out-of-plumbs of the brick ...

Back Analysis for Excavation-Induced Ground Movements Using a Direct Search Method

Back Analysis for Excavation-Induced Ground Movements Using a Direct Search Method

Evaluation of Rock Nail Wall Performance in Jointed Rock Using Numerical Method

The performance of excavation wall supported by nailing method is highly dependent on geological and geotechnical conditions of excavation area. In some cases, excavation area may be located in the jointed or weathered rocks. Joints are fractures of natural origin in the continuity of either a layer or body of rock http://en.wikipedia.org/wiki/Rock_(geology) that lacks any visible or measurable movement parallel to the surface plane of the fracture. Because of the low shear and tensile strengths of these discontinuities, as well as the looseness of a rock mass due to the unloading by excavation, rock masses can slide along these structural planes. It should be noted that excavation-induced ground movements are a major cause of deformation and damage to the existing buildings and utilities in the excavation affected zone. This paper concerns the performance of excavation walls supported by rock nails in rock masses having joints and damage levels of a structure adjacent to excavation area, using the results of numerical investigation. For this purpose, parameters such as wall deflections included cantilever and bulging displacements, settlement under structure and settlement ratio were investigated. In this regard, joints inclination and joints spacing effects were evaluated for this point. To evaluate the effects of mentioned parameters on the performance of excavation wall and building damage caused by wall deflections, a set of calibrated 2D finite element models were developed by considering all interactions between nail-rock-structure, anisotropic properties of jointed rock medium and staged construction process. This work was conducted over 100 developed models. The results of investigation indicated that different parameters such as anisotropy of rocks, joints inclination have significant effects on performance of excavation walls supported by rock nails, and damage levels of structures adjacent to the excavation area.