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Applicability of using GIN method, by considering theoretical approach of grouting design
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0002-3556-3562
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
2015 (English)In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529, Vol. 33, no 6, 1431-1448 p.Article in journal (Refereed) Published
Abstract [en]

In the practice of grouting of fractured rock, currently, empirical methods are used. Amongst them, the GIN method is popular mostly in Europe and has been tried in many projects. The concept of this method is to limit the combination of pressure and injected volume to a specific grout intensity number in order to control the energy induced in the rock fractures and to avoid uplift. However, difficulties in employing this method have been reported, which are mainly due to uncertainties in recognizing the distance of grout penetration and the state of the fractures during grouting and at the completion grouting. In this paper, the purpose has been examining the applicability of the GIN method by defining the characteristic curve of the P·V diagram (referred to here as the hyperbola) and suggesting appropriate completion criteria based on the radius of grout spread around the borehole. This will provide the chance to assign a permitted level of fracture deformation (or jacking) to the GIN by considering the formulation of fracture deformation based on grout propagation in a previously developed theoretical approach by Stille et al. (Geotech Geol Eng 30:603–624, 2012) as a part of the Real Time Grouting Control Method. Thus, in attaining the hyperbola, the identified radius of grout spread is achieved and the resulting fracture deformation at this completion point can be beneficial in improving penetrability. However, if the full extent of this deformation extends beyond the grouted zone, part of the fracture may remain un-grouted, and this will affect the sealing efficiency of the grouting program. This may be continued by selecting a smaller GIN and reducing the grouting pressure as the real time pressure–volume plot moves along the hyperbola, which will bring the fracture back to its initial state as grouting approaches the completion point, i.e. when the grout has spread to the desired distance. This hypothesis has been examined against the grouting works performed in three different real projects, for which the grouting parameters can be determined from the available grouting records. It is concluded that the GIN used in practice was much higher than the theoretically estimated values obtained through the proposed analytical solution. Furthermore, in the grouting of fractures close to the surface, the radius of grout spread impacts the GIN significantly, and only a limited grouting pressure is applicable, thus in using split spacing technique in such circumstances, different GINs should be selected for different sets of boreholes to obtain enough propagation at the maximum applicable pressure. The introduced analytical solution introduced in this paper can be a useful procedure for designing the GIN based on the grout spread. Nevertheless, it becomes complicated in dealing with fracture deformation. In a difficult grouting case where the demand for sealing is high, the recommendation is to use the proposed theoretical approach, which provides detailed information during the actual grouting procedure, by estimation of the radius of grout spread and the state of the fracture in real time

Place, publisher, year, edition, pages
Springer, 2015. Vol. 33, no 6, 1431-1448 p.
Keyword [en]
Fracture deformation, GIN method, Grout spread, Grouting pressure, Stop criteria, Theoretical approach
National Category
Geotechnical Engineering
URN: urn:nbn:se:kth:diva-155457DOI: 10.1007/s10706-015-9910-8ISI: 000364507900004ScopusID: 2-s2.0-84946025502OAI: diva2:761242

Updated from Manuscript to Article. QC 20160209

Available from: 2014-11-06 Created: 2014-11-06 Last updated: 2016-02-09Bibliographically approved
In thesis
1. Study of Pumping Pressure and Stop Criteria in Grouting of Rock Fractures
Open this publication in new window or tab >>Study of Pumping Pressure and Stop Criteria in Grouting of Rock Fractures
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Today practice of grouting is based on empirical approaches in that, pumping pressure and stop criteria are determined by benchmarking similar projects. Considering a maximum limit for grouting pressure would allow applying a relatively high pressure that may lead to jacking of the fracture or even uplift of the rock mass. On the other hand, keeping the pressure lower than the overburden, in order to avoid any deformation, will prolong grouting process. Determination of pumping pressure is more complicated considering the induced energy to the rock fracture due to combination of the injected volume and pumping pressure. In other word, pressurizing large volume of the injected grout with a low pumping pressure establish the same force inside the fracture as the high applied grouting pressure on small injected volume do. Therefore, an stop criterion to limit grouting volume along with grouting pressure, which is a hyperbola trimming maximum pressure-maximum volume limits and  named as grout intensity number (GIN), has been defined. However, in using this stop criterion and at completion point, the state of the fracture and the distance that grout spread inside the fracture are unknown. As a theoretical approach, examining the flow of the Bingham fluid in network of fractures led to development of a numerical model and later an analytical solution, which enabled estimation of distance that grout spread in the fractures in real time. Finally, theoretical curves to limit elastic and ultimate jacking were established to limit grout pressure in correlation with depth of grout penetration by considering the state of the fracture.  

Despite empirical and theoretical developments, determination of optimum grouting pressure is still challenging. In this study, In addition to examining performance of the analytical solution in estimation of grout spread and distinguishing onset of fracture jacking, the goal is coming up with recommendations for selection of optimum grouting pressure, by examining mechanism of elastic jacking. For this purpose, negative aspects of fracture deformation, which are increase of grouting time and remaining transmissivity, were quantified and discussed against its positive effect on increase of penetrability. By that, application of a relatively high pressure was recommended in order to opening of the fracture to a permitted level, with purpose of increasing penetrability while considering negative effects of elastic jacking. The stop criterion is defined as the grouting time of achieving the required distance of grout spread at the highest applicable grouting pressure.

In examining empirical methods, in grouting of fractures in deep levels, pressure-depth graph suggests usage of higher pressure in compare with the estimated pressure by theory while GIN method is conservative. In further studies GIN was estimated analytically and applying a relatively high grouting pressure in order to opening the fracture, up to attaining the hyperbola, and continuation of grouting with decreasing trend, in order to bringing the fracture back to its initial size at refusal, were proposed. Complexity of using this methodology in compare with theoretical approach was discussed.

As the future work, there is a need to verify the results in the field, and to confirm well performance of this analytical solution in different geologies. Examining variation of grout mixture properties during grouting program as well as significance of simplification of geological pattern to a single horizontal fracture, in that grout flow radially, are among other future studies that can develop this theoretical application further.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 42 p.
TRITA-JOB PHD, ISSN 1650-9501 ; 1020
Rock Mechanics, Grouting
National Category
Geotechnical Engineering
Research subject
Solid Mechanics
urn:nbn:se:kth:diva-155323 (URN)
Public defence
2014-11-21, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 14:00 (English)

QC 20141106

Available from: 2014-11-06 Created: 2014-11-04 Last updated: 2014-11-06Bibliographically approved

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