Induced Ground Deformation Research Articles

Numerical analysis of relative density effects on shallow TBM tunnel excavation: Ground behavior and principal strains at surface in greenfield conditions

Tunnel construction in urban areas may result in ground deformations that pose a risk to existing buildings and infrastructure; thus, accurate prediction of these induced ground deformations during the design phase is crucial. The paper focuses on the effects of sandy soil relative density on the ground deformations induced by tunnels excavated with Tunnel Boring Machines (TBMs). The study utilizes the Finite Element Method (FEM) and the NorSand model to simulate the behavior of a sandy ground. The validity of the FEM modeling approach is established by comparing predictions with results from six centrifuge tunnel tests from the literature. The centrifuge tests were performed on sand at different relative densities, tunnel diameters, and tunnel depths. The parameters for the NorSand model were determined based on laboratory tests. Only the state parameter was modified to achieve the desired relative density in the numerical simulations. The effects of relative density observed in centrifuge tests (Franza et al., 2019) have been numerically reproduced with no further adjustments of the model parameters. The rich outputs from the numerical models enabled an in-depth investigation of tunnel behavior, yielding new insights into how tunnels respond under varying relative densities, depths, and diameters. A comprehensive analysis of the induced ground deformations caused by shallow tunnels in sandy ground and the potential to damage buildings is included.

Liquefaction triggering and induced ground deformations at a metallurgical facility in Dörtyol-Hatay after the February 6 Kahramanmaraş earthquake sequence

The performance of a Metallurgical Facility located on the Dörtyol-Hatay coast is investigated from seismic soil liquefaction engineering perspective. The facility was shaken by the M7.8, and M7.6 Pazarcık and Ekinözü-Elbistan Kahramanmaraş earthquake sequence. This paper presents the assessment results of soil liquefaction triggering and induced ground deformations at the site. It discusses: i) the seismic response of the facility, more specifically, the surface manifestation of seismic soil liquefaction in the form of soil ejecta, ground deformations and displacements, mapped after the earthquake sequence, ii) the results of site investigation studies, performed prior to the events, iii) subsurface soil characterization of the site, iv) assessments of soil liquefaction triggering, v) analyses of liquefaction-induced ground settlements, lateral deformations and displacements, and vi) comparisons of them with those of the predicted. The case history performance documented herein, and the assessment results are believed to be useful in the development of case history-based predictive models for the assessment of liquefaction triggering and post-liquefaction ground deformations.

Energy tunnels: A review of the state of the art and knowledge gaps to harness renewable energy from underground infrastructure

The thermal activation of underground tunnels, also known as energy tunnels, has shown significant potential to harness geothermal and aerothermal energy as a low-carbon and economical solution for space heating and cooling, water heating and road de-icing. The heat and load transfer mechanisms in energy tunnels are, however, far less understood compared to other energy geostructures, due to their complex interaction with the ground and tunnel environment. This paper aims to provide a comprehensive overview of the current state of knowledge on the thermal and thermo-mechanical performance of energy tunnels based on recent analytical models, field tests, model-scale experiments, and numerical studies. Results suggest that a thermal yield ranging from 5 to 6 W/m2 is attainable for each degree Celsius difference between the fluid inlet temperature and the ground temperature in the presence of groundwater flow and tunnel airflow. In the reviewed studies, the thermally induced tunnel structural responses appear to be insignificant compared to those caused by tunnel excavation. However, the long-term thermally induced ground deformation in clay deposits can reach up to 15 mm, which may become a crucial issue and therefore needs to be examined in geotechnical design. As a new area of research, there is a lack of long-term experimental investigations to solidify the current knowledge of the thermal, structural and geotechnical performance of the system. Further research is also required to develop an integrated analysis and design method considering the techno-economic aspects and explore innovative business partnership models. This work can serve as a useful resource for researchers, engineers, and policymakers seeking to further develop and promote the adoption of this technology in infrastructure projects.

Deformations caused by subsurface heat islands: a study on the Chicago Loop

Deformations caused by subsurface heat islands: a study on the Chicago Loop

Developing software to assess the seismic risk of natural gas infrastructure: OpenSRA

As part of a multi-year study, the Pacific Earthquake Engineering Research (PEER) center in conjunction with Lawrence Berkeley National Laboratory (LBNL), the NHERI SimCenter at Berkeley, Slate Geotechnical Consultants (Slate), and several subcontractors, developed an open-source seismic risk analysis (OpenSRA) program that implements the performance-based earthquake engineering (PBEE) risk framework using a user-friendly interface, capable of operating on a desktop computer. This effort is made up of two elements: 1) research of seismic demand and capacity models, laboratory testing, and finite element modeling, and 2) implementing these findings into a backend calculation program with an easy-to-use interface. The NHERI SimCenter, Slate Geotechnical Consultants, and PEER researchers developed an integrative method to create an efficient code with a useful interface.OpenSRAimplements and updates current models addressing different forms of seismically induced ground deformation (e.g., fault rupture, liquefaction, and landslide) as well as ground shaking. It quantifies resistance to deformation in buried pipelines, well heads, caprocks, and aboveground components, and then provides a framework for estimating the uncertainty in both the models and parameters. The software allows the end-user to utilize these models according to the resolution of the available data (i.e., state-wide, regional, or site-specific). The interface provides a visualization of the inputs (e.g., ground motion, and liquefaction potential) and outputs (risk of leaks/breaks) overlaid on different maps of California.OpenSRAprovides the industry with updated seismic demand and capacity models, an efficient calculation method, and user-friendly software.OpenSRAenables end-users to estimate the risk of seismic damage to their infrastructure. Using risk-informed decisions enables utility owners to proactively and cost-effectively maintain infrastructure.

Seismic Induced Ground Deformation and Ionospheric Perturbations of the 29 July 2021, Mw 8.2 Chignik Earthquake, Alaska

AbstractThe subsurface, surface, and ionospheric characteristics associated with the 29 July 2021 Mw 8.2 Chignik Earthquake are studied in detail using continuous Global Positioning System (cGPS) data over Alaska. The cGPS‐inverted coseismic displacements demonstrate that the slip is distributed along the rupture area northeast of the epicenter with a maximum coseismic slip of ∼3.85 m occurring at a depth of ∼24.25 km. The vertical surface displacement estimated from the coseismic slip exhibits a similar deformation pattern with a maximum uplift of ∼1.0 m over the highly slip area. The ionospheric electron density perturbations associated with the Chignik earthquake were investigated using cGPS‐derived Total Electron Content (TEC) data. Unlike the northeast‐directed coseismic rupture and surface uplift, the ionospheric imprints of this event are more dominant southwest of the epicenter. This study reveals that the Earth's magnetic field and the ionospheric background electron density significantly controlled the TEC perturbation orientation and amplitudes rather than the rupture propagation and coseismic uplift pattern.

Ensuring face support and control in soft ground urban tunnels: FEM validation

AbstractWhen designing and constructing a tunnel in an urban setting with the use of a closed face Tunnel Boring Machine (TBM), the objective is to ensure both the tunnel face stability and the control of induced ground deformations within predefined, acceptable limits. Unless the exerted active face pressure will match the in situ ground stresses, there will be ground deformations taking place in the advance core, i.e., face extrusion and pre‐convergence, resulting in settlements or heave for active pressure lower or higher than the in situ stresses, respectively. This article presents the validation through finite element method (FEM) of an analytical methodology that can be applied on soft ground urban tunnels to assess the level of active face support to be considered in numerical analysis, to ensure elastic relaxation in the advance core and thus effective ground deformation control. The methodology combines the classic Anagnostou and Kovari method with the Convergence–Confinement method for face support proposed by Aristaghes and Autuori. In the current article, the methodology is described in detail and subsequently validated through three‐dimensional FEM analyses. The article concludes with a discussion on the results and the applicability range of the methodology.

3D numerical analysis of a masonry façade subjected to excavation- induced ground deformation

ABSTRACT To gain new insights to estimate the damage developed in a masonry façade founded on a strip footing due to adjacent excavation, a three-dimensional numerical study is carried out. An advanced hypoplastic (sand) constitutive model that takes account of small-strain stiffness is adopted. The responses of the masonry façade (which is perpendicular to the diaphragm wall) to excavation at different depths were investigated. The traction-separation behaviour of the cohesive element was employed to model the mortar joints. The computed results revealed that excavation adjacent to the masonry façade founded on a strip footing caused significant differential settlement in the masonry façade. As a result, the façade was subjected to damaging factors, which are induced by slope, tilting, and angular distortion. Consequently, cracks were developed in the façade on completion of the excavation. The maximum crack width (i.e., 8 mm) was developed at the top of the façade due to excavation.

Construction strategies for a NATM tunnel in São Paulo, Brazil, in residual soil

Due to the fast growth of urban areas worldwide, the demand for tunnels in developed areas is increasing. The design and construction of those tunnels are complex because of their shallow depths and their interaction with existing aboveground and buried structures, which results in rather limited allowable ground deformations induced by the tunnel excavation and support. In tropical regions, residual porous soils near the surface are common. Those soils are highly deformable; thus, tunneling may induce large ground deformations that may damage nearby structures. The new Austrian tunneling method (NATM) and the sprayed concrete lining (SCL) technique are being widely employed in several big cities in tropical regions, but little research has been conducted to assess the induced ground deformations in residual soils, common in tropical areas. This paper provides insight into this issue. A well-documented metro tunnel in São Paulo, Brazil, in a residual red porous clay, was analyzed using 3D finite element method (FEM). The behavior of the residual red porous clay was approximated by an advanced constitutive soil model calibrated with triaxial tests on intact samples extracted at the site. Predictions of the tunnel deformations during construction matched the field data. The calibrated model was then used to explore the tunnel performance under different construction strategies. The influence of partial face excavation, unsupported span length, support stiffness and pipe roof umbrella were assessed. The numerical results showed that partial face excavation was effective to reduce ground deformations ahead of the face of the tunnel and to improve face stability; however, the settlements behind the face increased because of the delay in closing the primary lining. The installation of a stiffer liner closer to the face reduced the ground deformations significantly. The pipe roof umbrella was the most effective technique to reduce the ground deformations around the tunnel; however, the numerical results did not consider deformations that could be induced by the drilling and grouting operations. The results shown in this paper provide both qualitative and quantitative information about the ground deformations induced by NATM tunneling in residual porous soils, that could help designers and contractors choose the optimum support and construction methods to minimize ground deformations.

The effects of unloading on drained cyclic behaviour of Sydney sand

New excavation or tunnelling affects the stress state of soils in ground. The change of stress state due to excavation may affect the cyclic behaviour of soils. Cyclic loading, such as traffic and earthquake loading, induced ground deformation may be greater than expected if such effect is not considered. A series of cyclic triaxial tests were performed on Sydney sand with different relative densities. The effect of unloading sequence on deformation of the sand under cyclic loading was simulated by reducing lateral stress in steps between loading cycles. The dependence of strain accumulation on the magnitude of confining pressure reduction and on unloading stress paths was studied. The results indicate that the sand has a memory of stress history and the stress history of such unloading enlarges the strain accumulation during the subsequent cycles, and the greater the reduction of lateral stress, the greater the accumulated strain. Under cyclic loading, the accumulated axial strain could increase nonlinearly or linearly with the ratio of unloading magnitude to initial mean effective stress, depending on the stress state before cyclic loading. The unloading stress paths have limited effects on the final accumulated strain if the initial and final stress states are the same. The variation of strain accumulation direction attributes to the change of average stress ratio resulting from lateral stress reduction, but hardly depends on relative density and unloading stress paths. The strain accumulation direction after unloading roughly agrees with the modified Cam Clay flow rule.

Investigation of effects of different construction sequences on settlement and load transfer mechanism of single pile due to twin stacked tunnelling

Construction of tunnels in urban cities may induce excessive settlement and tilting of nearby existing pile foundations. Various studies reported in the literature have investigated the tunnel-soil-pile interaction by means of field monitoring, centrifuge and numerical modelling, but the influence of construction sequence of twin stacked tunnelling on an existing pile is seldom reported in the literature. This paper presents a 3D coupled-consolidation numerical parametric analysis to understand settlement and load transfer mechanism in single pile due to twin stacked tunnelling with different construction sequences in stiff saturated clay. To accurately capture the tunnelling induced ground deformation, path- and strain-dependent soil stiffness at small strains were taken into account in each numerical analysis, by adopting an advanced hypoplastic clay model coupled with the inter-granular strain formulation. Twin stacked tunnelling was simulated one after the other with the first tunnel excavated near the mid-depth of the pile shift and the second either next to the toe of the pile (case ST) or below the pile (case SB). In addition, two more analyses were performed with change of construction sequence of twin stacked tunnels (i.e. cases TS and BS). The first tunnel was excavated either near the pile toe (case TS) or below the pile (case BS) and second tunnel near the mid-depth of the pile shaft. The different construction sequence of twin stacked tunnels at different depth had a substantial effect on induced pile deflection and settlement. In contrast, no significant effect was found on load transfer mechanism in the pile due to the change in construction sequence of tunnels.

A Spatial Mixing Model to Assess Groundwater Dynamics Affected by Mining in a Coastal Fractured Aquifer, China

A linear mixing model method based on principal component analysis (PCA) in three-dimensional space was used to assess groundwater dynamics. PCA was performed on a series of hydrochemical datasets collected from 2009 to 2014 (except in 2010). The results of PCA and a prior conceptual model were used to identify the evolution and potential end-members of water. Then, a mixing calculation code was applied to compute the mixing proportions, and the results were used to reconstruct the mixing process. Deviations were evaluated by comparing the computed and measured concentrations of ions. The accuracy of this method was compared to that of a 2D model that was based on only conservative ions and a 3D model developed in this study that does not consider the water’s physical parameters. The results indicated that the method that considered all of the measured ions, stable isotopes, and physical parameters, performed well. Its accuracy was demonstrated by good agreement between its measured and simulated values. The mean values of deviation for δ18O, δD, K, Na, Ca, Mg, Cl, and SO4 were 0.26, 0.51, 0.19, 0.08, 0.21, 0.15, 0.05, and 0.08, respectively. Five water sources and their groundwater dynamics were interpreted using this model; the results demonstrated that mining has had a substantial influence on the groundwater flow system in both the vertical and lateral directions. Above a depth of -375 m, freshwater is the dominant source, and its proportions in most sites exceeds 40%. Seawater has reached a depth of − 510 m, and its maximum proportion of 82% can be observed at 510-2a. Quaternary water recharged the area between F3 and the prospecting line 2230. Its proportion exceeded 45% at most sites. The recharge depth reached − 510 m at most sites and − 600 m at some sites. Calcium-rich and Mg-rich water were distributed above and below − 510 m, respectively. These distinguishing features indicate that induced ground deformation broke through the Quaternary aquifuge and increased the vertical recharge in the tensional zone, while preventing vertical recharge in the compressive zone at the subsidence center.

Analysis of PV Drains for Mitigation of Seismically Induced Ground Deformations in Sand Slopes

AbstractPrefabricated vertical (PV) drain arrays have been proposed as a minimally intrusive technique for mitigating seismically induced ground deformations in sandy liquefiable slopes. This paper...

Numerical modeling of tunneling induced ground deformation and its control

Tunnelling through cities underlain by soft soil, commonly associated with soil movement around the tunnels and subsequent surface settlement. The predication of ground movement during the tunnelling and optimum support pressure could be based on analytical, empirical or the numerical methods. The commonly used Earth pressure balance (EPB) tunneling machines, uses the excavated soil in a pressurised head chamber to apply a support pressure to the tunnel face during excavation. This face pressure is a critical responsibility in EPB tunnelling because as the varying pressure can lead to collapse of the face. The objective of the present study is to evalute the critical supporting face pressure and grout pressure by observing the vertical deformation and horizontal displacement of soil body during tunneling. The face pressure and grout pressures were varied to see how they might influence the magnitude of surface settlements/heave. A numerical model using PLAXIS-3D tunnel has been developed to analyse the soil movement around the tunnel that includes various geotechnical conditions. The ground surrounding the tunnel found to be very sensitive to the face pressure and grout pressure in terms of surface settlement and collapse of the soil body.

Hydro-mechanical influence of sub-seismic blind faults on integrity of CO2 geological storage in deep saline aquifer

Fluid injection in deep sedimentary porous formations might induce shear reactivation of reservoir faults. In this paper, we focus on ‘blind’ 1000-m-long normal faults (with limited shear displacement c.a. 1m), which can hardly be detected using conventional seismic surveys, but might potentially enable leakage pathways. In this study, a blind sub-seismic fault was assumed in the vicinity of a CO2 injection well (c.a. 1km). The study area is in the eastern part of the Paris Basin and targeting the Lower Triassic Sandstone formation which is deemed adequate for CO2 injection. The arbitrary geometry of the fault (with limited throw c.a. 1m), was set across the expected migration pathway of the injected CO2. The fault is assumed to extend vertically between the storage and control aquifer. A modeling approach coupling fluid flow and geomechanics is used to assess the pressure impact of the CO2 injection on in-situ fluids and formations. The model extends vertically from the Permian base to the ground surface assuming all layers to be homogeneous except in the storage aquifer where the heterogeneities of the braided channel environment are accounted for. The fault zone is modeled with heterogeneities both in the fault core and damage zones and the control aquifer and is explicitly gridded in the numerical model. In this study the fault core heterogeneities are assumed to be correlated to the Shale Gouge Ratio of the fault.The simulation scenarios aimed for a continuous CO2 injection at a rate of 0.8Mtpa during 30 years. When assuming the fault does not modify the formation flow and mechanical parameters, very little upward migration of CO2 is computed outside of the storage aquifer. This is not the case when the fault modifies the formation flow and mechanical parameters. In the latter case, the CO2 migrates up to the control aquifer preferably through the fault damage zones rather than through the fault core due to the parameter selection. In both cases, the pressure increase due to CO2 injection in the storage aquifer is small which imply small changes in effective stresses and negligible induced ground deformations. Most of the stress changes are limited to the vicinity of the fault and injection well.

Numerical Procedures for Simulating Earthquake Fault Rupture Propagation

AbstractNumerical simulations of earthquake fault rupture propagation can be used to design structures to resist damage from induced ground deformations. Several researchers have developed numerical models for analyzing the responses of soil and structures to underlying fault movement. Often, however, a relatively simple Mohr-Coulomb constitutive model that is modified to incorporate strain softening or other material nonlinearity is used. In this work, a modification of the UBCSAND soil constitutive model, one that has been shown to capture well the nonlinear shear response of soil for many stress paths, was used. The UBCSAND model was modified to add postpeak strain softening with a response that is dependent on the mode of fault rupture, a nonlinear failure envelope that is stress dependent, and a modified flow rule that is dependent on the mode of shear deformation. The numerical simulations captured well the observed trends in carefully performed geotechnical centrifuge experiments. The Modified-UBCS...

Distinguishing fluid injection induced ground deformation caused by fracture pressurization from porous medium pressurization

Ground deformation (both deformation patterns and deformation magnitudes) due to porous medium pressurization and fracture pressurization exhibits different characteristics. However, whether these differences can be detected during fluid storage is a complicated issue. Two analytical solutions have been previously developed to correlate ground deformation with underground fluid injection/extraction. One is Geertsma׳s (1973) solution on ground deformation associated with a disc-shaped reservoir (porous medium), and another is Sun׳s (1969) solution on ground deformation associated with a circular fracture. In this technique note, we compare these two solutions through a finite element modeling approach based on comparable boundary conditions, i.e., the similar areal extent , burial depth and fluid injection volume. We found that the deformation patterns are similar for these two cases on the ground surface, but very different underneath, especially in the horizontal direction. The radial extent of horizontal deformation is more restricted for the fracture pressurization case and more importantly, much higher magnitudes of ground deformation occur for the fracture pressurization case, which can provide new understanding of how to distinguish a fracture pressurization effect from porous medium pressurization. • Numerical tests are conducted to show ground deformation by fluid injection. • Two analytical solutions are compared based on comparable boundary conditions. • Deformation patterns are similar on the surface but very different underneath. • Higher magnitudes of ground deformation occur for the fracture pressurization case.

PERFORMANCE OF VACUUM CONSOLIDATION IN A THICK CLAYEY DEPOSIT IN SHANGHAI

A vacuum consolidation test was successfully carried out in a (more than 25 m) thick soft clayey deposit in Shanghai. At the site, there is a clayey silt layer located about 5.3 to 6.8 m depth with a relative higher hydraulic conductivity, and a cement deep mixing formed cut-off wall was able to prevent the vacuum leakage through this layer. Prefabricated vertical drains (PVDs) were installed with a spacing of 1.4 m and triangular pattern to a depth of 14 m. The measured results indicate that the degree of vacuum consolidation reached more than 90% in PVD improved zone for a period of about 38 days. Analysis results indicate that the vacuum pressure induced ground deformations can be calculated reasonably well by a previously proposed method. Further field monitoring results show that one month after stopping the vacuum loading, 10 to 65% of the vacuum pressure induced lateral displacement was rebounded, and the percentage rebounding increased with the depth.

Central Artery/Tunnel Project Excavation Induced Ground Deformations

Estimate of deformations around urban excavations is a primary concern for designers, contractors, owners, and potentially affected third parties. Significant efforts have gone into the development of empirically based methods to estimate deformations relying on a large number of case histories. The construction of the deep excavations for the central artery/tunnel project provides valuable information on observed deformations due to the construction of these excavations. Lateral deformations and surface settlements for three construction contracts are collected and summarized in a form similar to published empirical charts. The stiff support system used in these braced excavation and the embedment of the wall into stiff strata control deformations to minimal levels. The data show that surface settlements, although small, extend farther away from the excavation than previously reported.

Novel Approach to Integration of Numerical Modeling and Field Observations for Deep Excavations

Precedent and observation of performance are an essential part of the design and construction process in geotechnical engineering. For deep urban excavations designers rely on empirical data to estimate potential deformations and impact on surrounding structures. Numerical simulations are also employed to estimate induced ground deformations. Significant resources are dedicated to monitor construction activities and control induced ground deformations. While engineers are able to learn from observations, numerical simulations have been unable to fully benefit from information gained at a given site or prior excavation case histories in the same area. A novel analysis method, self-learning in engineering simulations (SelfSim), is introduced to integrate precedent into numerical simulations. SelfSim is an inverse analysis technique that combines finite element method, biologically inspired material models, and field measurements. SelfSim extracts relevant constitutive soil information from field measurements of excavation response such as lateral wall deformations and surface settlement. The resulting soil model, used in a numerical analysis, provides correct ground deformations and can be used in estimating deformations of similar excavations. The soil model can continuously evolve using additional field information. SelfSim is demonstrated using two excavation case histories in Boston and Chicago.