| 1. |
- Sundell, Jonas, 1984, et al.
(författare)
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Comprehensive risk assessment of groundwater drawdown induced subsidence
- 2019
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Ingår i: Stochastic Environmental Research and Risk Assessment. - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 33:2, s. 427-449
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Tidskriftsartikel (refereegranskat)abstract
- © 2019, The Author(s). We present a method for risk assessment of groundwater drawdown induced land subsidence when planning for sub-surface infrastructure. Since groundwater drawdown and related subsidence can occur at large distances from the points of inflow, the large spatial extent often implies heterogeneous geological conditions that cannot be described in complete detail. This calls for estimation of uncertainties in all components of the cause-effect chain with probabilistic methods. In this study, we couple four probabilistic methods into a comprehensive model for economic risk quantification: a geostatistical soil-stratification model, an inverse calibrated groundwater model, an elasto-plastic subsidence model, and a model describing the resulting damages and costs on individual buildings and constructions. Groundwater head measurements, hydraulic tests, statistical analyses of stratification and soil properties and an inventory of buildings are inputs to the models. In the coupled method, different design alternatives for risk reduction measures are evaluated. Integration of probabilities and damage costs result in an economic risk estimate for each alternative. Compared with the risk for a reference alternative, the best prior alternative is identified as the alternative with the highest expected net benefit. The results include spatial probabilistic risk estimates for each alternative where areas with significant risk are distinguished from low-risk areas. The efficiency and usefulness of this modelling approach as a tool for communication to stakeholders, decision support for prioritization of risk reducing measures, and identification of the need for further investigations and monitoring are demonstrated with a case study of a planned railway tunnel in Varberg, Sweden.
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| 2. |
- Dahlin, Torleif, et al.
(författare)
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Mapping of quick clay by ERT and CPT-R in the Göta Älv river valley
- 2014
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Ingår i: Landslides in Sensitive Clays. - Dordrecht : Springer Netherlands. - 2213-6959 .- 1878-9897. - 9789400770782 - 9789400770799 ; 36, s. 217-228
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Bokkapitel (refereegranskat)abstract
- Within clay prone areas it is important to know if and to what extent quick clay is present. In Sweden undisturbed sampling and laboratory investigations are used to determine clay sensitivity and identify quick clay. Recent research for mapping of quick clay areas with the resistivity method is based on the fact that low pore-water salinity constitutes a criterion for quick clay formation. Electrical resistivity tomography (ERT) is an established geophysical method that provides an overview of the resistivity in large volumes, but resolution decreases rapidly with depth. CPT-R probes (Cone Penetration Test with Resistivity module) on the other hand can register the resistivity with very high resolution continuously along the probed depth. In a known quick clay area along the Göta river in Gothenburg, Sweden, both ERT and CPT-R were used to evaluate possible synergy effects when the results were combined. Field investigations comprised 11 CPT-R soundings and five parallel ERT profiles, each 400 m long. The results gave good agreement between the methods down to depths of 10–15 m. Below that the CPT-R probe generally registered lower values than the ERT inverted resistivity models. The results from ERT comply with the value of 6 Ωm as a lower threshold value for possible quick clay formation in Sweden. From CPT-R measurements this value was found to be approximately 3 Ωm. The discrepancy appears to be related to sulphide content and may have measurement technical explanations or be due to the differences in chemical composition. The results show that a combination of ERT and CPT-R provides an efficient approach for mapping of possible quick clay volumes. It can be an integral part of an optimized detailed geotechnical investigation program, and form a decision basis for where to do undisturbed sampling for laboratory analyses. It also opens possibilities for correlation between resistivity and mechanical parameters via the CPT-R results.
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| 3. |
- Tornborg, Johannes, 1984, et al.
(författare)
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Benchmarking of a contemporary soil model for simulation of deep excavations in soft clay
- 2019
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Ingår i: Proceedings of the XVII European Conference on Soil Mechanics and Geotechnical Engineering. - 9789935943613
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Konferensbidrag (refereegranskat)abstract
- Measurement data from previous excavation works in soft clay deposits are revisited to benchmark a contemporary constitutive soil model, referred to as the Creep-SCLAY1S. The research is motivated by the planned deep excavations for the West Link tunnel in Gothenburg that require analyses of both short- and long-term performance. Unique data on prior excavation works, which were instrumented and monitored during the construction period, will be utilised. In contrast to previous studies, that focused on the construction period, also the long-term performance will be assessed using satellite data. The analyses are carried out using a contemporary rate-dependent model, considering the on-going (background) creep deformations in the clay deposit. The study shows that while the recent model developments result in improved predictions, additional features need to be further developed: most notably, the formulations for the rate-dependent small strain stiffness in loading and unloading stress paths requires attention. Also, it is evident that modelling details, such as installation effects (sheet pile wall and pre-cast concrete displacement piles) are important for prediction of the subsequent response.
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| 4. |
- Tornborg, Johannes, 1984, et al.
(författare)
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Experience from short-and long-term performance of deep excavations in soft sensitive clays
- 2021
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Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 710:1
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Konferensbidrag (refereegranskat)abstract
- Design of excavations and permanent underground structures requires accurate predictions of e.g. deformations and earth pressures for both the short-and long-term. As excavation depths increase and/or the proximity to adjacent infrastructure decreases, there is a need to improve and develop existing design methods and validate numerical models. The first part of this paper revisits the measurement data from a previous excavation, the Göta Tunnel in Gothenburg, Sweden, in order to benchmark a contemporary constitutive soil model, called Creep-SCLAY1S. This study looks into time series including e.g. final dewatering of the excavation, followed by the development of pore water pressures, earth pressures and deformations over time (until 2 years after excavation). The model predictions are in general in good agreement with the measurement data up to final dewatering. However, installation effects due to drilling are believed to have caused continued deformations which are difficult to capture in the numerical model. Part two of the paper presents details of a recently instrumented excavation in soft clay in Central Gothenburg. The measurement data comprises e.g. pore water pressures, deformations as well as vertical and horizontal earth pressures at three locations under the permanent structure. Continued long-term measurements are planned and the existing and future data are believed to provide valuable insights on the development of the stress state and earth pressures under permanent structures in soft clay.
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| 5. |
- Tornborg, Johannes, 1984, et al.
(författare)
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Modelling the construction and long-term response of Göta Tunnel
- 2021
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Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 134
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a benchmark of a rate-dependent constitutive model for soft soils, implemented in a 2D finite element code, against the response of an instrumented excavation in sensitive clay: Göta Tunnel in Gothenburg. The monitoring data, which comprise time-series of pore water pressures, displacements, earth pressures and strut forces, provide valuable insights of the time-dependent response during the construction period. The long-term response, in terms of the ongoing settlement rates, is assessed using remote sensing data. The results of the numerical simulations demonstrate that the constitutive model, Creep-SCLAY1S, is capable of capturing the observed response. The trends of vertical and horizontal displacements are captured well until the stage of dewatering, and the evolution of pore pressures and earth pressures is computed with high accuracy, excluding peaks in the measurement values arising from pile and rock anchor installation. Most importantly, the results demonstrate that the rate-dependent model enables to model the complete service life of the tunnel, from construction of the excavation to the tunnel operation, with one unified model parameter set. Furthermore, the comparisons highlight the importance of assessing installation effects both in the choice of construction methods and modelling.
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| 6. |
- Tornborg, Johannes, 1984
(författare)
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On the temporal evolution of earth pressures in deep excavations in soft clay
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Urbanisation and sustainable development of cities drives the need to increasingly utilise underground space. Consequently, there is more demand for deeper and larger excavations in urban areas, pushing the limits of current engineering experience. The vast majority of the reported observations of earth pressures in deep excavations, however, are on lateral earth pressures only and cover the construction stage. Reports on the performance in the serviceability stage are scarce, especially for underground structures in soft clays. In particular, there is a lack of investigations on the evolution of earth pressures below permanent structures at the base of deep excavations. Additionally, quantifying the magnitude and evolution of earth pressures due to delayed heave restrained by structural elements, remains challenging. This thesis investigates the temporal evolution of earth pressures acting on underground structures in deep excavations in soft clay, by means of field monitoring and numerical analyses. The ultimate goal is to generalise the results and develop non-dimensional design charts that quantifies the magnitude and evolution of earth pressures beneath the base of deep excavations and underground structures. The research consists of three parts i) benchmarking of a soil model (Creep-SClay1S) against the observed response of two well-documented excavations, ii) field monitoring of the hydro-mechanical response of soil elements below the base of an excavation and underground structure, and iii) a parametric study, using the Finite Element Method, designed and evaluated using dimensionless parameter groups to generalise the results. The first part demonstrates that the Creep-SClay1S model can be used to compute the magnitude and evolution of earth pressures acting on underground structures in soft clays with sufficient accuracy. Subsequently, the field monitoring of the hydro-mechanical response with clustered instruments enabled unique observations of the evolution of effective stresses and the stress ratio K =σ’h/σ’v at soil element level. The parametric study quantifies the impact of the normalised time between the end of excavation and the completion of the restraining structure at the base of the excavation on the emerging magnitude of the effective heave pressures for several scenarios. The results compare well to the field monitoring data and physical model tests. The work presented in this thesis reveals the mechanisms that control the development and evolution of earth pressures in deep excavations. The combination of field monitoring, dimensional analysis and the numerical modelling of the system response have been integrated into design charts. The results can readily be used as a tool for industry to assess the magnitude of effective heave pressure and complement detailed project-specific analyses.
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| 7. |
- Tornborg, Johannes, 1984, et al.
(författare)
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Permanent Sheet Pile Wall in Soft Sensitive Clay
- 2023
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Ingår i: Journal of Geotechnical and Geoenvironmental Engineering - ASCE. - 1090-0241 .- 1943-5606. ; 149:6
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Tidskriftsartikel (refereegranskat)abstract
- Reports on the serviceability stage and long-term performance of embedded retaining structures are scarce, even more so in areas with background settlements. This paper presents a case study of an excavation with a permanent sheet pile wall in soft sensitive clay in Uppsala, Sweden. The monitoring data span the short-term and four years of the serviceability stage. The monitoring data are compared with finite element analyses using the rate-dependent Creep-SClay1S model. A historic groundwater drawdown is accounted for in the modeling and challenges with respect to the proper initialization of the in situ stress state, preconsolidation pressure, fabric, and bonding are discussed. The results show that even though the background settlements are somewhat underpredicted, the horizontal displacements as well as anchor forces were captured rather accurately. This valuable case study of the short- and long-term behavior of a permanent sheet pile wall in soft sensitive clay confirms the performance of using this cost-effective solution for a permanent construction. Furthermore, the paper highlights the challenges of an accurate description and modeling of the initial in situ state.
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