Gunnar Gustafson

Prediction of groutability from grout properties and hydrogeological data

Abstract Sealing tunnels and caverns in fractured crystalline rocks has been considered notoriously unpredictable and possible to manage only through experience and intuitive knowledge. Words such as “witchcraft” and “black art” have been used ironically in Sweden to describe the state of the art. In this paper, initially grout penetration and grout take in parallell planar fractures are discussed. General expressions for these entities are also derived for fractures with varying width. In this paper, the grout take of a system of inhomogeneous channels in a fracture plane is studied further and the grout takes of such systems are modelled numerically. Grout takes are calculated for increased variability of the fracture aperture and the influence of this is assessed. In normal Swedish grouting procedures, the grouting boreholes are tested by water pressure tests (WPT). The hydrogeological information from these tests can be transferred to grouting apertures, and thus yield design information for grouting operations. Finally, the applicability of the findings is evaluated using field data from grouting of the access tunnel of the Aspo Hard Rock Laboratory, Sweden. The conclusion is that field methods for prediction and design of grouting operations can successfully be based on the theory.

Application of New Theories and Technology for Grouting of Dams and Foundations on Rock

Permeation grouting is used to improve rock conditions under dams and foundations. During recent decades, there has been a substantial increase of understanding of the mechanism behind grout spread in fractured rock. It is the penetrability of the grout mix and the spread in the joints which will be the governing factors for the quality of the grout curtain. The flow properties and the pressure will give the required time to achieve the quality. The empirical based refusal and completion criteria of today can be replaced by a more engineering based grouting process. An active control method has been developed in order to govern the grout spread during the grouting operation based on the new theory of spreading of grout. The concept is called the “real time grouting control method”. The concept and the latest finding of the mechanism of spreading of the grout in the fractures of the rock mass are presented in the paper. The application of the method on two dam projects is also presented.

Steering Parameters for Rock Grouting

In Swedish tunnel grouting practice normally a fan of boreholes is drilled ahead of the tunnel front where cement grout is injected in order to create a low permeability zone around the tunnel. Demands on tunnel tightness have increased substantially in Sweden and this has led to a drastic increase of grouting costs. Based on the flow equations for a Bingham fluid the penetration of grout as a function of grouting time is calculated. This shows that the time-scale of grouting in a borehole is only determined by grouting over-pressure and the rheological properties of the grout, thus parameters that the grouter can choose. Pressure, grout properties and the fracture aperture determine the maximum penetration of the grout. The smallest fracture aperture that requires to be sealed thus also governs the effective borehole distance. Based on the identified parameters that define the grouting time-scale and grout penetration an effective design of grouting operations can be set up.

A new stochastic model for fracture transmissivity assessment

A new stochastic model is proposed for fracture counts and transmissivities in a borehole interval. This new model incorporates several empirical observations, including: (i) Clustering of fractures; (ii) Exponential fracture spacings; (iii) Transmissivities extending over several orders of magnitude; (iv) Power law probability tail for transmissivities at finer scales; (v) Log-normal transmissivities at larger scales; and (vi) Dependence between fracture counts and transmissivities. Several example applications are provided using borehole data from Sweden

Äspö Hard Rock Laboratory—Research, development and demonstration for deep disposal of spent nuclear fuel

Abstract The Aspo Hard Rock Laboratory (Aspo HRL) provides an important scientific and technical basis for the programme o f implementation and operation of a future deep repository for spent nuclear fuel in Sweden. A major milestone has now been reached with the completion of the pre-investigation and construction phases. The comprehensive research conducted has permitted valuable development and verification of site characterization methods applied from the ground surface, boreholes and underground excavations. The present database of the crystalline rock at the Aspo area is one of the most comprehensive databases in the world, containing data from a large number of investigation methods from the surface down to 1700 m below ground level. Site characterization in conjunction with construction work at Aspo has basically confirmed the pre-construction models. The work at Asp

A swedish grouting design concept: Hydraulic testing and selection of grout

has shown that such pre-construction models can be obtained for the studied key issues through the application of “standard methodology of good quality” for measurements, data analyses, modelling and evaluation The site characterization at Aspo has been a realistic “adress-rehearsal” that will be invaluable for planning and executing surface and underground site characterization for the deep repository for spent fuel in Sweden.

A Swedish Grouting Design Concept: Decision Method for Hard Rock Tunneling

Some grouting boreholes take no grout and some boreholes take too much, two extremes related to grouting technique, grout properties and the properties of fractures intersecting the boreholes. Successful sealing of rock and soil demands an adequate description of the system to be grouted as a basis for grouting design and selection of grouting material. The basis for this Swedish concept of grouting design is the individual fractures and the hydraulic apertures, b, of these fractures. The hydraulic aperture is an important parameter to describe the grouting behavior and is used to determine if the grout can enter the fractures, the penetrability. The hydraulic aperture also determines the penetration length in addition to grout parameters e.g. yield stress, τ0, and viscosity, μg as well as grouting pressure and time. Knowing these parameters, a proper grouting technique can be adapted. Important input for both design and performance are simple and practical tests of rock and grout and the intention of this paper is to present a testing procedure and give examples from laboratory and field experiences that the approach actually works.

A Swedish grouting design concept: Grouting with silica sol in the Nygård and Törnskog tunnels

Efficient grouting of hard rock requires adequate knowledge of the water-bearing fracture system in the rock mass. The observational method approach involves identifying different possible scenarios and relating them to predefined strategies for grouting design. Parameters useful in preparing a relevant description of the rock mass are presented, as well as a method for choosing a conceptual model. The implications of different fracture systems for the grouting design are discussed. A method is presented for deciding whether grouting is needed in order to ensure a high degree of probability that tunnel leakage will remain below the inflow requirements. The methods presented are applied to data from a real tunnel to illustrate the procedures.

Fracture Deformation Measurements during Grouting in Hard Rock

The scope of this paper is to present two tunnel grouting design case studies where the waterproofing aimed not only to reduce the water inflow to a specified level, but to minimize the number of dripping spots by means of pre-excavation grouting. Every grouted section of around one hundred meters in both tunnels used relevant parameters from the rock and the grout material properties to develop an adequate, pre-excavation grouting design. Both tunnels, constructed in crystalline rock, used silica sol as the main grouting material and were evaluated later by means of control boreholes and dripping characterization. Control boreholes showed a decrease in the transmissivity in these sections, and the dripping characterization showed a reduction in the number of dripping spots compared to the rest of the tunnel, where this pre-excavation grouting concept was not used. This led to minimization of the number of drains used, which was clearly visible in the Nygard case, suggesting that the designs were successful and confirming that an understanding of the rock and grout properties is crucial to the design concept.

Stop Criteria for Cement Grouting

When a fracture system in crystalline rock is grouted the rock mass may deform. Such deformations may reduce the grouting efficiency since new flow paths are opened. The work presented here show that deformations occur at hydraulic tests and grouting and that deformation can be measured and evaluated as stiffness from in situ tests. Deformation measurements, hydraulic testing, and grouting was conducted in spring 2010 in the Hallandsas tunnel and hydraulic testing in a service tunnel in Gothenburg (Runslatt and Thorn, 2010). For measuring physical deformation recently developed equipment from Chalmers University of Technology was used. Deformations were measured seven times in the same borehole. Three measurements were during grouting, and the remaining four from water pressure tests. Most deformations occurred at pump pressures of 1-1.4 MPa, which is lower than the calculated normal rock stress. Stiffness has been evaluated in several ways, including a new method, (Fransson, et al., 2010). Generally the evaluated stiffness is lower in the Hallandsas tunnel than in the Gothenburg tunnel. The results show agreement with other in situ experiments.