Excavation-induced Settlements Research Articles

Finite-Element Investigation of Excavation-Induced Settlements of Buildings and Buried Pipelines

Finite-Element Investigation of Excavation-Induced Settlements of Buildings and Buried Pipelines

Hydro-mechanical behavior of a deep excavation with dewatering and recharge in soft deposits

Dewatering is mandatory for deep excavations above confined aquifers. Artificial recharge is then commonly used to alleviate the adverse impacts of dewatering. Together, these construction technologies complicate stratum responses including groundwater flow and stratum deformations. This study conducted a coupled hydro-mechanical numerical analysis on a case history of a deep excavation with dewatering and recharge construction measures. The numerical model and input parameters were validated by field data. Results of drawdown distributions, pore pressure variations, vertical effective stress and stratum deformations were analyzed in association with construction activities. It is found that the drawdown of the confined aquifer was closely correlated to dewatering and recharge activities. The excavation-induced settlement mainly occurred in soft soil layers, whereas the stratum deformation induced by dewatering and recharge occurred in the aquifer and adjacent aquitards. The distinct stratum responses could be attributed to different changes in pore pressure and effective stress induced by excavation, dewatering and recharge.

Role of Shear Deformability on the Response of Tunnels and Pipelines to Single and Twin Tunneling

Tunneling can compromise the safety and serviceability of existing buried infrastructure because of settlements, crack openings, dislocations, and material strains. A continuum-based soil-structure interaction model, implementing an equivalent Timoshenko beam, is used to evaluate the excavation-induced settlements and longitudinal deformations of existing tunnels and pipelines. Both single and twin tunneling scenarios are examined. The shear flexibility of shield and sprayed concrete lining tunnels may be significant. This increases tunneling-induced settlements while it decreases tilt, curvature, and the associated bending moment, with implications for optimal monitoring installations. In this work, a new dimensionless shear factor is introduced, governing the relative importance of shear and bending deformations and accounting for the settlement trough width. This can be used to evaluate if a pure-bending, shear-dominated, or mixed deformation mode should be expected. Design charts to assess existing infrastructure affected by either single or twin tunnels are proposed.

InSAR monitoring data to assess building response to deep excavations

Recently, there has been growing interest to use Interferometric Synthetic Aperture Radar (InSAR) to quantify ground displacements. While InSAR can well determine the area and magnitude of subsidence, very little attention has been paid to explore InSAR measurements to assess the building response adjacent to geotechnical works (e.g., deep excavations, tunnelling). Specifically, few studies have investigated the ability of using InSAR to derive widely accepted building deformation parameters including angular distortion and horizontal strain. On the other hand, geotechnical engineers generally use traditional monitoring data to assess the behaviour of existing structures adjacent to excavations, but often only spatially and temporally limited monitoring data exist to reliably evaluate the governing mechanisms. This contribution follows a case study approach to explore the value of InSAR to quantify the effects of excavation-induced settlements on buildings. Conventional monitoring data of structures adjacent to excavation works for a construction project in Oslo, Norway, are compared to InSAR measurements from satellites with different spatial resolutions and from two different processing methods. Differences between displacements obtained from these different InSAR monitoring datasets and their practical implementation are discussed. Building deformations and respective damage categories are then quantified using a methodology that combines both InSAR and inclinometer measurements. As expected, it was found that high resolution InSAR measurements are more reliable when assessing the building response to excavation works.

Assessment of building damage due to excavation-induced displacements: The GIBV method

This paper presents an original methodology for the rapid assessment of “potential” building damage caused by an excavation. The combination of the Ground-work Impact (GI), in terms of induced greenfield displacements, and the Building Vulnerability (BV) form the basis for the GIBV damage assessment method. Both short- and long-term displacements are considered in the impact evaluation. In addition to short-term displacement due to undrained shear deformations, groundwater drawdown can result in significant consolidation settlements at considerable distance from the excavation site. In the proposed method for soft soil ground conditions, the short-term excavation-induced settlement is derived using empirical expressions and long-term displacement is estimated by coupling empirically-derived relationships for excavation-induced groundwater drawdown with a soil stratification model and consolidation theory. The building vulnerability is assessed by considering different physical characteristics and conditions of the buildings.The GIBV method has been implemented in a GIS tool to predict damage classes for buildings exposed to excavation-induced settlements. Two different case studies in Norway were used to test the reliability of the predictions of the tool and validate the methodology. A comparison between the predicted damage classes with the back-calculated ones shows a relatively high accuracy of the methodology. Moreover, the coupled model, which considers both impact and vulnerability for the damage assessment of buildings, has a higher accuracy and lower overestimation rate compared to the results obtained by just considering the impact.

Effect of pipe characteristics in umbrella arch method on controlling tunneling-induced settlements in soft grounds

Abstract Recent developments in tunneling have stimulated design practitioners to more effectively utilize the underground spaces. However, tunneling at shallow depth in soft grounds gives rise to concerns associated with tunnel instability. Umbrella arch method (UAM), as a pre-reinforcement approach of tunnels in complex geological conditions, is widely used to maintain the tunnel stability. Quantitative assessment of the impacts of the entire approach and forepoling pipe features on tunnel stability remains challenging due to the complex nature of the UAM application. This study aimed to assess the effect of pipe design parameters on reinforcing the tunnels excavated in soft grounds. This practical investigation considered the actual field conditions attributed to the tunneling procedure and UAM deployment. Then, the tunneling process was modeled and the tunnel excavation-induced settlements were calculated. The post-processed results confirmed that deploying the UAM substantially reduced the tunnel crown and ground surface settlements by 76% and 42%, respectively. Investigation of various design parameters of pipes underscored the significance of incorporating the optimum value for each individual parameter into design schemes to more effectively control the settlements. Additionally, contrasting the settlement reduction rates (SRRs) for pipe design variables showed that the tunnel stability is more sensitive to the changes in the values of diameter and length, compared to values of the installation angle and center-to-center distance of the pipes.

Predicting Excavation-Induced Settlement for Embedded Footing: Case Study

Predicting Excavation-Induced Settlement for Embedded Footing: Case Study

Erratum for “Excavation-Induced Settlement and Tilt of a 3-Story Building” by Yue Choong Kog

Erratum for “Excavation-Induced Settlement and Tilt of a 3-Story Building” by Yue Choong Kog

Selection, production, and testing of scaled reinforced concrete models and their components

This paper presents considerations and procedures for the selection, production, and testing of small-scale, reinforced concrete frames to maintain geometric and kinematic similitude. To verify the proposed solutions, 1/10th scaled models were subjected to adjacent excavation-induced settlements in 1-gravity, soil-structure experiments. Material scaling strategies were verified by comparing the resultant surface soil settlements with published studies and by comparing the model building response with numerical simulation, as well as the extent of the damage with previously established thresholds.

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 ...

Performance of an Overexcavated Metro Station and Facilities Nearby

This paper examines the performance of an overexcavated metro station in soft clay within Shanghai metropolitan area, in which there are many high-rise buildings and buried utility pipelines in the proximity. The excavation was supported by stiff concrete diaphragm walls braced by steel pipes. The measured performance included deflections of diaphragm walls, ground settlements, and settlements of the adjacent buildings and utility pipelines. On the basis of daily monitored data, the effects of overexcavation on wall deflections, deflection rates, and the locations in which the maximum wall deflections and the maximum wall deflection rates occurred were investigated. For those buildings in the proximity, the heavy high-rise steel-reinforced concrete buildings supported by deep foundations experienced limited uniform settlements, whereas the light brick buildings resting on shallow foundations experienced substantial total and differential settlements. For the adjacent utility pipelines, the excavation-induced settlements were relatively uniform.

Predicting RC Frame Response to Excavation-Induced Settlement

In many tunneling and excavation projects, free-field vertical ground movements have been used to predict subsidence, and empirical limits have been employed to evaluate risk. Validity of such approaches is largely unknown given that ground movements are in fact not one-dimensional and that adjacent applied loads are known to have an impact. This paper employed analytical and large-scale experimental efforts to quantify these issues, in the case of excavation adjacent to a reinforced concrete frame with tieback anchors and a sheetpile wall in dry sand. With this flexible system, a disproportionate amount of the soil and building movements occurred prior to installation of the first tieback, even when conservative construction practices were applied. Furthermore, free-field data generated a trough as little as one-half the size of that recorded near the building frames. Empirically based relative gradient limits generally matched the extent and distribution of the damage, while the application of various structural limits did not fully identify local damage distribution but did generally reflect global response. The use of fully free-field data or a failure to include lateral soil displacements both underpredicted building displacements by as much as 50% for low-rise concrete frames without grade beams on sand.

Reliability Analysis and Updating of Excavation-Induced Ground Settlement for Building Serviceability Assessment

In this paper, the excavation-induced settlement determined by the KJHH model, a recently developed semiempirical model, is used to assess the serviceability reliability of adjacent buildings. The calculated settlement, considered as the load in the context of reliability analyses in this paper, is compared with a tolerable settlement, considered as the resistance herein. The reliability of the adjacent building against “damage” (defined herein as the violation of serviceability requirements such as having intolerable settlement) is first analyzed and the probability of exceedance (i.e., exceeding the tolerable settlement) is calculated. Furthermore, as the excavation proceeds, observed settlement at the current excavation stage is used to update the prediction of settlement at subsequent stages, and the probability of exceedance is updated accordingly.

Building response to excavation-induced settlement : Boscardin, M D; Cording, E J J geotech engng div ASCEV115, N1, Jan 1989, P1–21

Building response to excavation-induced settlement : Boscardin, M D; Cording, E J J geotech engng div ASCEV115, N1, Jan 1989, P1–21