| 1. |
- Holmberg, M., et al.
(författare)
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Evaluation of pre-grouting for the city line project using the RTGC method
- 2012
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Ingår i: ISRM International Symposium - EUROCK 2012. - : International Society for Rock Mechanics.
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Konferensbidrag (refereegranskat)abstract
- An access tunnel for the City Line project in Stockholm was excavated in the early parts of 2010. The works also included pre-grouting with cement. The performance of pre-grouting operation was evaluated for 14 continuous fans that included 326 grouted holes. A method called “Real Time Grouting Control (RTGC)”was used in the analysis. It is shown how the RTGC method can be used to investigate the effectiveness of existing stop criteria. It is first time an evaluation using RTGC carried out in this magnitude. The water inflow to the tunnel after grouting satisfied requirements. The grouting effect is quantified by assessments of the average conductivity of the rock mass and of the grout spread outside the tunnel. The evaluation indicates that the stop criteria in the design were chosen conservatively relative to the achieved grouting results. A model is discussed where the required grout spread is used as a design parameter to quantify the potential for reducing the pumping time.
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| 5. |
- Stille, Björn, 1969, et al.
(författare)
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Experiences With Real Time Grouting Control Method
- 2010
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Ingår i: Bergmekanikdag : föredrag vid Bergmekanikdag i Stockholm 8 mars 2010.. - 0281-4714. ; , s. 119-132
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In the paper the concept of “Real Time Grouting Control Method” is described in order to calculate the grout penetration and to control grouting in real time by applying developed theories for grout spread. The stop criterion can with this method be related to achieved groutspread such as the fact that grouting is completed when the grout penetration for the smallest fracture that has to be sealed is above a certain minimum value (target value) or before the grout penetration for the largest fracture aperture reaches a certain maximum value (limitingvalue).It might also be possible by following the ongoing grouting minute by minute to predict the course of the grout flow and spread and also analyze the risk for uplift and jacking. These issues will also be discussed in the paper.Verification of the “Real Time Grouting Control Method”, with field data from four tunnel projects in Sweden is presented in the paper. The calculated flow dimensionality, the calculated fracture apertures and the calculated grout flows were quite close to thosemeasured. This indicates that the “Real Time Grouting Control Method” may be applicable to real grouting design and control.
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| 6. |
- Alejano, L. R., et al.
(författare)
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Rock engineering design and the evolution of Eurocode 7
- 2013
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Ingår i: ISRM International Symposium - EUROCK 2013. - : International Society for Rock Mechanics. - 9781138000803 ; , s. 777-782
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Konferensbidrag (refereegranskat)abstract
- The Eurocode for Geotechnical Design, EN-1997-1:2004, informally known as Eurocode 7 or EC7, was fully implemented within the European Union in 2010. This Eurocode is intended to apply to all geotechnical engineering design, including rock engineering. In recognition that all codes must continue to evolve in order to remain applicable, and the long time that such evolution takes, work is already underway under the auspices of the European Committee for Standardisation, CEN, to identify how the code should develop for future revisions. This paper presents a summary of the maintenance procedures for Eurocodes in general and the specific maintenance work currently being undertaken on EC7 in respect of rock engineering design. It also highlights potential future development of EC7, and the need for enthusiastic involvement by the European rock engineering community to direct these developments.
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| 7. |
- Bagheri, Mehdi, et al.
(författare)
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A new analytical solution based on joint relaxation for analyzing symmetrical block stability
- 2013
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Ingår i: International Journal for Numerical and analytical in geomechanics. - : Wiley. - 0363-9061. ; 37:8, s. 771-786
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Tidskriftsartikel (refereegranskat)abstract
- The magnitude of clamping forces has a significant influence on the estimated ultimate pullout force of a block. The Crawford–Bray equation, which is fundamental in considering clamping forces, is only a function of horizontal stress and block height. Further research to incorporate the influence of induced stress in block stability analysis was considered, but all the previous analytical solutions for analyzing block stability assume a continuum medium to estimate clamping forces and do not allow joint deformations to occur before block movement due to gravity. Assuming a continuous medium to estimate clamping forces leads to an overestimation of block stability and therefore unsafe design. In this paper, an attempt has been made to deepen the understanding of the block failure mechanism and correct the estimated magnitude of clamping forces in a discontinuous medium. A conceptual model is proposed based on the loading–unloading of the block from an in-situ state to failure. Based on this model, an analytical solution has been developed that calculates clamping forces in a discontinuous medium. The validity and model uncertainty of the solution were checked for different conditions. The new analytical solution is both precise and accurate and can be used as a design tool to estimate block stability.
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| 8. |
- Bagheri, Mehdi
(författare)
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Block stability analysis using deterministic and probabilistic methods
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a discussion of design tools for analysing block stability around a tunnel. First, it was determined that joint length and field stress have a significant influence on estimating block stability. The results of calculations using methods based on kinematic limit equilibrium (KLE) were compared with the results of filtered DFN-DEM, which are closer to reality. The comparison shows that none of the KLE approaches– conventional, limited joint length, limited joint length with stress and probabilistic KLE – could provide results similar to DFN-DEM. This is due to KLE’s unrealistic assumptions in estimating either volume or clamping forces. A simple mechanism for estimating clamping forces such as continuum mechanics or the solution proposed by Crawford-Bray leads to an overestimation of clamping forces, and thus unsafe design. The results of such approaches were compared to those of DEM, and it was determined that these simple mechanisms ignore a key stage of relaxation of clamping forces due to joint existence. The amount of relaxation is a function of many parameters, such as stiffness of the joint and surrounding rock, the joint friction angle and the block half-apical angle. Based on a conceptual model, the key stage was considered in a new analytical solution for symmetric blocks, and the amount of joint relaxation was quantified. The results of the new analytical solution compared to those of DEM and the model uncertainty of the new solution were quantified. Further numerical investigations based on local and regional stress models were performed to study initial clamping forces. Numerical analyses reveal that local stresses, which are a product of regional stress and joint stiffness, govern block stability. Models with a block assembly show that the clamping forces in a block assembly are equal to the clamping forces in a regional stress model. Therefore, considering a single block in massive rock results in lower clamping forces and thus safer design compared to a block assembly in the same condition of in-situ stress and properties. Furthermore, a sensitivity analysis was conducted to determine which is the most important parameter by assessing sensitivity factors and studying the applicability of the partial coefficient method for designing block stability. It was determined that the governing parameter is the dispersion of the half-apical angle. For a dip angle with a high dispersion, partial factors become very large and the design value for clamping forces is close to zero. This suggests that in cases with a high dispersion of the half-apical angle, the clamping forces could be ignored in a stability analysis, unlike in cases with a lower dispersion. The costs of gathering more information about the joint dip angle could be compared to the costs of overdesign. The use of partial factors is uncertain, at least without dividing the problem into sub-classes. The application of partial factors is possible in some circumstances but not always, and a FORM analysis is preferable.
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| 9. |
- Bagheri, Mehdi, et al.
(författare)
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Investigation of model uncertainty for block stability analysis
- 2011
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Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - : Wiley. - 0363-9061 .- 1096-9853. ; 35:7, s. 824-836
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Tidskriftsartikel (refereegranskat)abstract
- The application of probabilistic design, such as FORM, is expanding rapidly in the design of geotechnical structures. The analytical solution proposed by Crawford and Bray for analyzing block stability can be used as a performance function to carry out probabilistic design. The solution benefits from considering both clamping forces and joint stiffness. However, imperfect assumptions and simplifications in the solution generate model uncertainties. The amount of model uncertainty must be considered in order to assess a reliable design. The purpose of this paper is to identify when the analytical solution is applicable and quantify the model uncertainty of the solution. The amount of model uncertainty for the analytical solution has been assessed for different conditions. The results show that at a shallow depth with a low value of in situ stress ratio (horizontal stress/vertical stress), the analytical solution predicts that the block is stable whereas DEM shows that the block is unstable. The results of the analyses indicate that in cases with low stress ratio, cases with high anisotropy of joint stiffness or the case of a semiapical angle close to the friction angle, the accuracy of the analytical solution is low. Neglecting key parameters, such as the absolute value of joint shear and normal stiffness, vertical in situ stress and its influence on joint relaxation generate model uncertainty in the analytical solution. The analyses show that by having more information about the key parameters, the model uncertainty factor could be identified more precisely.
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| 10. |
- Draganović, Almir, et al.
(författare)
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Bleeding and bleeding measurement of cement-based grout
- 2012
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Ingår i: Grouting and deep mixing 2012. - Reston, VA : American Society of Civil Engineers (ASCE). - 9780784412350 ; , s. 1681-1690
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Konferensbidrag (refereegranskat)abstract
- Grouting is a common method of sealing rock in various geotechnical projects, and the bleeding of cement-based grout is an often-discussed issue. Current cylinder measuring methods for the estimation of the bleeding of cement-based grouts originate from the measurement of the bleeding of cement pastes used in ordinary building practices. Whether bleeding measured with these methods is relevant to bleeding in small fractures in rocks is one of the main questions in this study. This study showed that the bleeding process is very complex and is governed by different physical and chemical processes like sedimentation, consolidation, flocculation and hydration. It also showed that consolidation has little influence on bleeding in fractures. Bleeding in fractures is mainly the result of sedimentation. In addition, the study showed that the results measured using cylinder methods are not relevant for the bleeding of grout in fractures and that voids in the fractures caused by bleeding can be refilled during grouting. The bleeding should occur to a considerably lower extent in rock fractures, if it occurs at all.
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