Håkan Stille

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.

Support of weak rock with grouted bolts and shotcrete

Abstract This paper presents a closed form elastoplastic analytic solution of grouted bolts considering four different approaches to bolt performance. The equations consider bolt loads and displacements round a circular opening subjected to hydrostatic pressure. The solutions allow for the interaction of bolts and a shortcrete lining. The analytic results are compared with bolt load data and readings obtained from instrumented bolts and extensometers in the Kielder Experimental tunnel excavated in mudstone. Two different support systems are included in the study, one with grouted bolts and one with grouted bolts together with shotcrete. The bolt load distribution obtained from the analytic solutions show good consistency with the measured results for two of the four different theoretical solutions. The analytic solutions that correspond to the measured values take into account the existing low bond strength between rock mass and bolt and the effects of local deformations in the rock mass under the end plate. It is shown, that a good contact between the rock surface and the end plate have effects on the magnitude of the bolt load and that it is important to use grout of high quality to secure the transfer of load from rock mass to the bolt. The displacement values, obtained from extensometers installed together with the two different support systems, coincide with the deformations obtained from the corresponding analytic solution.

Numerical calculations for prediction of grout spread with account for filtration and varying aperture

Grouting as a mean to reduce the ingress of water to underground facilities has been used for decades. With an increased demand for tightness and cost efficiency, the incentive to improve the metho ...

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.

A Method for Measuring and Evaluating the Penetrability of Grouts

This paper suggests a method for measuring the penetrability of grouts. The proposed method evaluates the penetrability of the grout based on measurements with a newly developed device where the grouts ability to pass filters of different widths is measured. After evaluation two especially descriptive parameters are obtained, a minimum and a critical aperture. These two parameters describes the penetrability of the grout and can be used for comparing grouts and in modelling grout propagation. In the paper some measurements and evaluated results are presented. This is to study some governing factors for the penetrability of grouts but the main objective is to demonstrate the proposed method. The results confirms that the main factor governing the penetrability is the type of cement used and that variations in w/c ratio and addition of superplasticizers only have limited influence. Measurements on the filter cake shows that the thickness and the density are influenced by pressure and w/c ratio.

Controlling grout spreading in tunnel grouting — analyses and developments of the GIN-method

In order to choose the best grouting technique, predictions of the grouting result can be made. Due to uncertainties in the predictions, control of the grouting during ongoing work is an important ...

COMPUTER-SIMULATED FLOW OF GROUTS IN JOINTED ROCK

Abstract This article presents a model for simulating grout propagation in jointed rock. The joint planes are described as channel networks initially filled with water. The grouth can be either a Bingham or a Newtonian fluid, with time-dependent properties. The presentation includes the mathematical base for the model and some practical examples. The practical examples include testing of a grouting method based on manipulations of the groundwater level, a comparison of results when using grouts having different rheological properties, and a comparison of pre- and post-grouting.

Rheological properties of microfine cement grouts

Abstract This paper describes a measuring technique, based on rotational viscometry, that can be used to evaluate the flow properties of grouts. The technique has been used on cement grouts, assuming the Bingham model. The paper discusses field equipment that can be used easily to estimate the flow properties on site. The results shown indicate the effect on the flow properties by different admixtures and additives. It is concluded that an increase in specific surface and addition of bentonite will increase both the yield stress and the plastic viscosity. Plasticizing admixtures reduce the yield stress and the plastic viscosity. By combining bentonite and plasticizers in the grout, improved flow properties (i.e., low yield stress, low plastic viscosity) can be achieved.

Design and excavation of rock caverns for fuel storage—a case study from Zimbabwe

Abstract This article summarises the design and construction of an unlined underground fuel storage facility in Harare, Zimbabwe. The paper focuses on geological, hydrogeological and rock mechanical issues related to the project. Special attention has been paid to the design and excavation of two large silos for jet fuel storage.

CLASSIFICATION OF JOINTED ROCK WITH EMPHASIS ON GROUTING

Abstract This article includes the mathematical foundations of a proposed geometrical model describing the rock, and shows how the geometrical properties of the rock mass can be evaluated. The base for evaluating the parameters describing the rock mass can be a continuous recording of the flow and pressure for a grout hole during a grouting session. Recorded data are then fitted to a mathematical function that describes the flow in the geometrical model. A rough estimation of the geometrical properties can also be done from the volume of injected grout, combined with ordinary water pressure tests. The evaluated geometry can be used to classify the rock.