Vinayagamoorthy Sivakumar, Pratiksha Pandey, Snehasis Tripathy, Jonathan Black, Paul Dunlop, Kyle McKee
Many available ground improvement techniques are effective, but involve large amounts of carbon dioxide emissions. Any green ground improvement technique would thus be beneficial. In this work, dry air, supplied at low pressure and relative humidity, was used to remove water from a soft soil deposit. The investigation was carried out at model scale, with a soft soil layer formed in a box of size 1.0 × 1.0 × 0.75 m. The soil bed was fitted with slender granular columns for the injection of dry air. The technique is the reverse process of vacuum consolidation, in which the magnitude of negative pore water pressure that can be applied to the soil is limited and thus requires careful construction procedures. The dry-air approach is simple and does not require any complex construction procedures. The investigations carried out over a limited period showed a significant improvement in the strength of the soil bed, indicating possible full-scale implementation. Full-scale implementation of the technique may not require any new construction methods as the procedure is very similar to that adopted in vacuum consolidation. However, variabilities in ground conditions, including the groundwater table, may pose additional challenges and supplementary information (soil–water characteristic data and numerical modelling) may be necessary to implement this technique at full scale.
{"title":"Dry-air technology for stabilising weak deposits","authors":"Vinayagamoorthy Sivakumar, Pratiksha Pandey, Snehasis Tripathy, Jonathan Black, Paul Dunlop, Kyle McKee","doi":"10.1680/jgeen.21.00231","DOIUrl":"https://doi.org/10.1680/jgeen.21.00231","url":null,"abstract":"Many available ground improvement techniques are effective, but involve large amounts of carbon dioxide emissions. Any green ground improvement technique would thus be beneficial. In this work, dry air, supplied at low pressure and relative humidity, was used to remove water from a soft soil deposit. The investigation was carried out at model scale, with a soft soil layer formed in a box of size 1.0 × 1.0 × 0.75 m. The soil bed was fitted with slender granular columns for the injection of dry air. The technique is the reverse process of vacuum consolidation, in which the magnitude of negative pore water pressure that can be applied to the soil is limited and thus requires careful construction procedures. The dry-air approach is simple and does not require any complex construction procedures. The investigations carried out over a limited period showed a significant improvement in the strength of the soil bed, indicating possible full-scale implementation. Full-scale implementation of the technique may not require any new construction methods as the procedure is very similar to that adopted in vacuum consolidation. However, variabilities in ground conditions, including the groundwater table, may pose additional challenges and supplementary information (soil–water characteristic data and numerical modelling) may be necessary to implement this technique at full scale.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138495405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tunnel lining is usually installed with delay behind the tunnel face excavation, which requires that a displacement has to be considered at the tunnel boundary before the support structure installation. This delayed installation comes with a release and redistribution of stress in the rock mass. Internal tunnel lining forces significantly rely on the stress relaxation process taking place in the rock mass surrounding the excavated tunnel. One of the difficulties when designing tunnel supports is, therefore, to analyze the rock-support interaction considering the tunnel lining convergence caused by the stress redistribution. In this study, a simple and effective calculation process based on the combination of two methods, the Hyperstatic Reaction Method (HRM) and Convergence Confinement Method (CCM), is presented to analyze the interaction of rock mass and support structure. The rock mass is assumed to obey the Hoek-Brown criterion. The stress release is also taken into consideration in the present method. The present method is validated by comparing results of the HRM in terms of tunnel lining forces against the analytical ones. Thereafter, the effect of the stress release coefficient, of the tunnel depth and of the Hoek-Brown criterion parameters (the Geological Strength Index (GSI) and σci), on the lining internal forces are presented and discussed.
{"title":"Design of Deep Rock Tunnels combining the Hyperstatic Reaction and Convergence Confinement methods","authors":"D. Du, D. Dias, N. Do","doi":"10.1680/jgeen.22.00051","DOIUrl":"https://doi.org/10.1680/jgeen.22.00051","url":null,"abstract":"Tunnel lining is usually installed with delay behind the tunnel face excavation, which requires that a displacement has to be considered at the tunnel boundary before the support structure installation. This delayed installation comes with a release and redistribution of stress in the rock mass. Internal tunnel lining forces significantly rely on the stress relaxation process taking place in the rock mass surrounding the excavated tunnel. One of the difficulties when designing tunnel supports is, therefore, to analyze the rock-support interaction considering the tunnel lining convergence caused by the stress redistribution. In this study, a simple and effective calculation process based on the combination of two methods, the Hyperstatic Reaction Method (HRM) and Convergence Confinement Method (CCM), is presented to analyze the interaction of rock mass and support structure. The rock mass is assumed to obey the Hoek-Brown criterion. The stress release is also taken into consideration in the present method. The present method is validated by comparing results of the HRM in terms of tunnel lining forces against the analytical ones. Thereafter, the effect of the stress release coefficient, of the tunnel depth and of the Hoek-Brown criterion parameters (the Geological Strength Index (GSI) and σci), on the lining internal forces are presented and discussed.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73889563","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Peng-Cheng Wang, Xiaotian Yang, Jian Zhang, Xueyan Ge
This paper investigates the clogging effect of soil pile in vacuum preloading of dredged soil combined with a prefabricated vertical drain (PVD) through laboratory model tests and analytical model. Variation in water content and permeability of soil around the PVD clarify the formation of soil pile. Seepage and consolidation tests with a formed soil pile indicate that the clogging effect slows down the drainage of pore water rather than stops it. Taking soil pile as a filter layer, an analytical model is established incorporating the clogging effect, varying permeability and compressibility of soil. Finally, based on comparison between existing cases and the analytical model, an empirical linear relationship is suggested for estimating the likely range of the permeability and scale of soil pile against the reduction of void ratio in the vacuum- assisted consolidation of soil. It is clarified that the proposed model with suggested parameters could simulate the consolidation process of soil with high water content appropriately. The soil pile with lower permeability or larger diameter leads to more serious clogging effect on the consolidation of soil. The development in clogging effect due to the extension of soil pile decreased persistently.
{"title":"Analysis for vacuum consolidation of soil incorporating clogging effect, varying permeability and compressibility","authors":"Peng-Cheng Wang, Xiaotian Yang, Jian Zhang, Xueyan Ge","doi":"10.1680/jgeen.21.00237","DOIUrl":"https://doi.org/10.1680/jgeen.21.00237","url":null,"abstract":"This paper investigates the clogging effect of soil pile in vacuum preloading of dredged soil combined with a prefabricated vertical drain (PVD) through laboratory model tests and analytical model. Variation in water content and permeability of soil around the PVD clarify the formation of soil pile. Seepage and consolidation tests with a formed soil pile indicate that the clogging effect slows down the drainage of pore water rather than stops it. Taking soil pile as a filter layer, an analytical model is established incorporating the clogging effect, varying permeability and compressibility of soil. Finally, based on comparison between existing cases and the analytical model, an empirical linear relationship is suggested for estimating the likely range of the permeability and scale of soil pile against the reduction of void ratio in the vacuum- assisted consolidation of soil. It is clarified that the proposed model with suggested parameters could simulate the consolidation process of soil with high water content appropriately. The soil pile with lower permeability or larger diameter leads to more serious clogging effect on the consolidation of soil. The development in clogging effect due to the extension of soil pile decreased persistently.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85808493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, numerical analyses of connected and disconnected piled- raft foundations (PRFs) comprising of single pile, 2×1, 3×1, 2×2, 3×2, 3×3 and 5×5 pile groups subjected to different lateral loads with a constant vertical load have been carried out by a three- dimensional finite element analysis. Results from the present analysis have been validated with reported field studies considering vertical load and reported experimental studies considering lateral load. The reported multilayered sub-soil profile has been considered for the analysis. Parametric studies in terms of effect of variation in pile length (L/d=20, 30, 39), spacing of piles in the pile group (S/d=3, 5, 6), number of piles, thickness of raft (0.5m, 1.2m, 2m), variation of axial force, excess pore water pressure, bending moment and shear force along depth of piles for connected and disconnected PRFs have been discussed for a time period of 20 years. The horizontal connected piled- raft coefficients have been determined corresponding to the lateral deflections. Generalised equation has been predicted for the horizontal connected PRF coefficient.
{"title":"Long term effect of vertical and lateral loads on piled raft foundations: A case study","authors":"Kajal Tarenia, N. Patra","doi":"10.1680/jgeen.22.00030","DOIUrl":"https://doi.org/10.1680/jgeen.22.00030","url":null,"abstract":"In this study, numerical analyses of connected and disconnected piled- raft foundations (PRFs) comprising of single pile, 2×1, 3×1, 2×2, 3×2, 3×3 and 5×5 pile groups subjected to different lateral loads with a constant vertical load have been carried out by a three- dimensional finite element analysis. Results from the present analysis have been validated with reported field studies considering vertical load and reported experimental studies considering lateral load. The reported multilayered sub-soil profile has been considered for the analysis. Parametric studies in terms of effect of variation in pile length (L/d=20, 30, 39), spacing of piles in the pile group (S/d=3, 5, 6), number of piles, thickness of raft (0.5m, 1.2m, 2m), variation of axial force, excess pore water pressure, bending moment and shear force along depth of piles for connected and disconnected PRFs have been discussed for a time period of 20 years. The horizontal connected piled- raft coefficients have been determined corresponding to the lateral deflections. Generalised equation has been predicted for the horizontal connected PRF coefficient.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89539072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In recent decades, numerical calculations are often used to optimize from a technical and economical point of view the design of underground works. Nowadays, using these tools permits to obtain efficient and affordable designs. The simulation of the tunneling procedure in case of the use of a tunneling boring machine and in urban areas is a complex soil/structure interaction problem. The use of continuum numerical methods is then required. In this paper, a three-dimensional code using finite differences is used. The reference case of this study is the Lyon metro line D project in France where a non-symmetric load is present at the surface due to the presence of a retaining wall. An accurate on-site monitoring system was set up to assess ground movements during the mechanized excavation of twin tunnels. The collected data is used as a reference to show the validity and accuracy of the developed three-dimensional model. A procedure that simulates the segmental lining installation is developed to simulate the tunneling process. Two constitutive models were used to simulate the soil behavior: Plastic Hardening (PH) and linear elasticity with perfect plasticity (Mohr-Coulomb shear failure criterion). The simpler soil constitutive model shows some drawbacks which can be eliminated by using the Plastic Hardening. The existence of a retaining wall induces a non-symmetric load condition; however, the settlement trough predicted by advanced numerical models shows a good agreement with the monitoring data one.
{"title":"Twin earth pressure balance tunneling – Monitoring and numerical study of a soft soil urban case","authors":"M. Nematollahi, D. Dias","doi":"10.1680/jgeen.21.00165","DOIUrl":"https://doi.org/10.1680/jgeen.21.00165","url":null,"abstract":"In recent decades, numerical calculations are often used to optimize from a technical and economical point of view the design of underground works. Nowadays, using these tools permits to obtain efficient and affordable designs. The simulation of the tunneling procedure in case of the use of a tunneling boring machine and in urban areas is a complex soil/structure interaction problem. The use of continuum numerical methods is then required. In this paper, a three-dimensional code using finite differences is used. The reference case of this study is the Lyon metro line D project in France where a non-symmetric load is present at the surface due to the presence of a retaining wall. An accurate on-site monitoring system was set up to assess ground movements during the mechanized excavation of twin tunnels. The collected data is used as a reference to show the validity and accuracy of the developed three-dimensional model. A procedure that simulates the segmental lining installation is developed to simulate the tunneling process. Two constitutive models were used to simulate the soil behavior: Plastic Hardening (PH) and linear elasticity with perfect plasticity (Mohr-Coulomb shear failure criterion). The simpler soil constitutive model shows some drawbacks which can be eliminated by using the Plastic Hardening. The existence of a retaining wall induces a non-symmetric load condition; however, the settlement trough predicted by advanced numerical models shows a good agreement with the monitoring data one.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73024255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Newman, Oscar Hueso Cuberos, Mikel Martinez Goirigolzarri
An 8.8 m diameter earth pressure balance tunnel boring machine has been used to construct a 7.6 km section of the Thames Tideway Tunnel through central London, UK, between Battersea and Bermondsey. Two major geological structures: the Lambeth Anticline and the London Bridge Fault Zone have imposed significant changes in the tunnel face geology. The tunnel boring machine was continually monitored for operating parameters, such as cutterhead torque, thrust and injection of spoil conditioning additives. This led to the recognition of the structures, in addition to a high frequency of sand channels within the upper Lambeth Group strata. The monitoring led to validation of the preconstruction geological model and in conjunction with inspection of the tunnel face during scheduled interventions and geological logging of several interception shafts, has provided valuable assurances for the predicted ground ahead of tunnelling operations.
{"title":"Effects of changing geology on the performance of a Thames Tideway tunnel boring machine","authors":"T. Newman, Oscar Hueso Cuberos, Mikel Martinez Goirigolzarri","doi":"10.1680/jgeen.22.00060","DOIUrl":"https://doi.org/10.1680/jgeen.22.00060","url":null,"abstract":"An 8.8 m diameter earth pressure balance tunnel boring machine has been used to construct a 7.6 km section of the Thames Tideway Tunnel through central London, UK, between Battersea and Bermondsey. Two major geological structures: the Lambeth Anticline and the London Bridge Fault Zone have imposed significant changes in the tunnel face geology. The tunnel boring machine was continually monitored for operating parameters, such as cutterhead torque, thrust and injection of spoil conditioning additives. This led to the recognition of the structures, in addition to a high frequency of sand channels within the upper Lambeth Group strata. The monitoring led to validation of the preconstruction geological model and in conjunction with inspection of the tunnel face during scheduled interventions and geological logging of several interception shafts, has provided valuable assurances for the predicted ground ahead of tunnelling operations.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75921023","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yongsheng Wang, Xiaobin Zhang, Bin Wang, Jianshe Liu
In current studies, when calculating the stability of a permeable dam under half-full or full reservoir conditions, seepage force has not been considered. Based on the stability calculation equation of a new debris flow grille dam structure, combined with the accumulation seepage model and the Bernoulli principle, the simplified expression of seepage force was derived, and its effect on the dam body was found to be equivalent to the overturning moment; thus, the original calculation equation was corrected. The effect of changing the internal friction angle on the stability was analyzed, making the corrected equation universal and applicable. The verification results showed that the overturning stability coefficient of the blocking dam was positively correlated with the internal friction angle. Compared to the original calculation equation, the anti-overturning stability coefficient of the blocking dam was reduced by about 44.5% on average after considering the seepage force; the attenuation amplitude increased with the increase of the friction angle in the accumulation, which was closer to the actual stress situation.
{"title":"Stability Correction Calculation of New Debris Flow Grille Dam Considering Permeation","authors":"Yongsheng Wang, Xiaobin Zhang, Bin Wang, Jianshe Liu","doi":"10.1680/jgeen.21.00219","DOIUrl":"https://doi.org/10.1680/jgeen.21.00219","url":null,"abstract":"In current studies, when calculating the stability of a permeable dam under half-full or full reservoir conditions, seepage force has not been considered. Based on the stability calculation equation of a new debris flow grille dam structure, combined with the accumulation seepage model and the Bernoulli principle, the simplified expression of seepage force was derived, and its effect on the dam body was found to be equivalent to the overturning moment; thus, the original calculation equation was corrected. The effect of changing the internal friction angle on the stability was analyzed, making the corrected equation universal and applicable. The verification results showed that the overturning stability coefficient of the blocking dam was positively correlated with the internal friction angle. Compared to the original calculation equation, the anti-overturning stability coefficient of the blocking dam was reduced by about 44.5% on average after considering the seepage force; the attenuation amplitude increased with the increase of the friction angle in the accumulation, which was closer to the actual stress situation.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89115353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper discusses the use of vacuum consolidation to improve soft ground and increase its undrained shear strength (Su). Since soft soils, particularly peat and organic clay soils, have very low Su values, the construction of embankments and structures on these soils often cause ground failure. For the trial embankment conducted in this research project, soft ground composed of peat, organic clay and clay was improved by using vacuum consolidation, resulting in a significant increase in Su values, and an embankment 10.7 m in height could be constructed on the improved ground without causing ground failure. The initial Su values of the peat and organic clay were lower than the strength of the clay, namely, 48% (peat) and 59% (organic clay) of that of clay. However, after vacuum consolidation of these soils, their final Su values greatly increased to 199% (peat) and 154% (organic clay) of the final strength of clay. It was demonstrated that the increased Su was the result of synergy of the relatively high normalized undrained shear strength (Su/σ′v, where σ′v is the effective overburden stress) of peat and organic clay, and the unique loading mechanism of vacuum consolidation. It was also demonstrated that in case of a relatively narrow embankment (e.g., road embankment and river levee), the effect of isotropic consolidation also contributes to increase the stability of the vacuum consolidated peaty ground. It was also found that if the (Su/σ′v)NC of the original ground and the over-consolidation ratio (OCR) are known, the (Su/σ′v)OC of the given ground over-consolidated by vacuum consolidation can be predicted.
{"title":"Increasing the Undrained Shear Strength of Soft Ground Improved by Vacuum Consolidation","authors":"H. Hayashi, Hijiri Hashimoto","doi":"10.1680/jgeen.21.00154","DOIUrl":"https://doi.org/10.1680/jgeen.21.00154","url":null,"abstract":"This paper discusses the use of vacuum consolidation to improve soft ground and increase its undrained shear strength (Su). Since soft soils, particularly peat and organic clay soils, have very low Su values, the construction of embankments and structures on these soils often cause ground failure. For the trial embankment conducted in this research project, soft ground composed of peat, organic clay and clay was improved by using vacuum consolidation, resulting in a significant increase in Su values, and an embankment 10.7 m in height could be constructed on the improved ground without causing ground failure. The initial Su values of the peat and organic clay were lower than the strength of the clay, namely, 48% (peat) and 59% (organic clay) of that of clay. However, after vacuum consolidation of these soils, their final Su values greatly increased to 199% (peat) and 154% (organic clay) of the final strength of clay. It was demonstrated that the increased Su was the result of synergy of the relatively high normalized undrained shear strength (Su/σ′v, where σ′v is the effective overburden stress) of peat and organic clay, and the unique loading mechanism of vacuum consolidation. It was also demonstrated that in case of a relatively narrow embankment (e.g., road embankment and river levee), the effect of isotropic consolidation also contributes to increase the stability of the vacuum consolidated peaty ground. It was also found that if the (Su/σ′v)NC of the original ground and the over-consolidation ratio (OCR) are known, the (Su/σ′v)OC of the given ground over-consolidated by vacuum consolidation can be predicted.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73880047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The most important issue regarding the safety and performance of concrete face rockfill dams (CFRDs) is to determine stresses and deformations. However, predictions of crest settlements of concrete face rockfill dams (CFRDs) are usually performed by using empirical relationships. Since, in recent years, CFRDs are constructed much higher and more complicated topographical and geological dam sites, these require performing numerical analysis to evaluate the stress and deformations in the entire dam body. Numerical estimation of deformations and crest settlements is also crucial particularly to determine parapet wall heights and freeboard allowances at the design stage. In addition, assessing long-term rockfill behavior and the concrete face membrane crack potential are important for post construction dam safety. The objective of this study is to evaluate post-construction deformations and crest settlements of a high concrete faced rockfill dam under two different loading cases considering nonlinear elasto- plastic behavior of the rockfill structure. As constitutive model, Duncan-Chang hyperbolic stress-strain model was applied in finite element simulations considering the failure criterion is isotropic and hardening. Calibration of the rockfill's hyperbolic parameters was performed by comparing the calculated displacements with the actual settlement measurements from the instruments. Computed crest settlements were also compared with those of some CFRDs given in the literature. Calculated crest settlement and other deformations were in good agreement with the rockfill settlement measurements and in acceptable ranges, and do not threat the dam's safety.
{"title":"Post-Construction Safety Assessment of a High Concrete Face Rockfill Dam","authors":"Ergin Erayman, U. S. Cavus, M. Yildiz","doi":"10.1680/jgeen.21.00167","DOIUrl":"https://doi.org/10.1680/jgeen.21.00167","url":null,"abstract":"The most important issue regarding the safety and performance of concrete face rockfill dams (CFRDs) is to determine stresses and deformations. However, predictions of crest settlements of concrete face rockfill dams (CFRDs) are usually performed by using empirical relationships. Since, in recent years, CFRDs are constructed much higher and more complicated topographical and geological dam sites, these require performing numerical analysis to evaluate the stress and deformations in the entire dam body. Numerical estimation of deformations and crest settlements is also crucial particularly to determine parapet wall heights and freeboard allowances at the design stage. In addition, assessing long-term rockfill behavior and the concrete face membrane crack potential are important for post construction dam safety. The objective of this study is to evaluate post-construction deformations and crest settlements of a high concrete faced rockfill dam under two different loading cases considering nonlinear elasto- plastic behavior of the rockfill structure. As constitutive model, Duncan-Chang hyperbolic stress-strain model was applied in finite element simulations considering the failure criterion is isotropic and hardening. Calibration of the rockfill's hyperbolic parameters was performed by comparing the calculated displacements with the actual settlement measurements from the instruments. Computed crest settlements were also compared with those of some CFRDs given in the literature. Calculated crest settlement and other deformations were in good agreement with the rockfill settlement measurements and in acceptable ranges, and do not threat the dam's safety.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86233117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Victor Hugo Franco Rattia, S. Divall, G. Gitirana, A. Assis
Soft-ground Tunnel Boring Machines (TBM) are the preferred solution for construction of long tunnels and linear infrastructure assets, especially in urban areas. TBMs allow the control of tunnel face stability, minimizing effects on the surrounding ground. Unfortunately, the existing methods for the assessment of ground surface movements due to TBM tunnelling either utilise complex and computationally expensive numerical analyses or rely on simplistic volume loss theories, which do not consider characteristics of the ground and TBM operation. This paper presents a simple formulation to estimate the immediate surface settlement due to the applied TBM support pressure, based on an analogy with the hyperbolic behaviour of stress-strain curves of soils. The maximum surface settlement and volume loss were the variables chosen to describe the ground movement while the TBM face support pressure describes the tunnel internal support pressure. Uncertainties due to the inherent variability of geotechnical parameters were also considered, resulting in definition of lower and upper boundaries. Data from a series of centrifuge test results, with and without tunnel face reinforcement by forepoles and a real scale TBM case study were used to validate the proposed model. The analyses show that the proposed model adequately represented the observed settlement data.
{"title":"Estimating settlements due to TBM tunnelling","authors":"Victor Hugo Franco Rattia, S. Divall, G. Gitirana, A. Assis","doi":"10.1680/jgeen.21.00103","DOIUrl":"https://doi.org/10.1680/jgeen.21.00103","url":null,"abstract":"Soft-ground Tunnel Boring Machines (TBM) are the preferred solution for construction of long tunnels and linear infrastructure assets, especially in urban areas. TBMs allow the control of tunnel face stability, minimizing effects on the surrounding ground. Unfortunately, the existing methods for the assessment of ground surface movements due to TBM tunnelling either utilise complex and computationally expensive numerical analyses or rely on simplistic volume loss theories, which do not consider characteristics of the ground and TBM operation. This paper presents a simple formulation to estimate the immediate surface settlement due to the applied TBM support pressure, based on an analogy with the hyperbolic behaviour of stress-strain curves of soils. The maximum surface settlement and volume loss were the variables chosen to describe the ground movement while the TBM face support pressure describes the tunnel internal support pressure. Uncertainties due to the inherent variability of geotechnical parameters were also considered, resulting in definition of lower and upper boundaries. Data from a series of centrifuge test results, with and without tunnel face reinforcement by forepoles and a real scale TBM case study were used to validate the proposed model. The analyses show that the proposed model adequately represented the observed settlement data.","PeriodicalId":54572,"journal":{"name":"Proceedings of the Institution of Civil Engineers-Geotechnical Engineering","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89902260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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