ABSTRACT:

Chemical injection grouts are used more and more frequently underground in order to stabilize jointed rock masses. The two grouts polyurethane resin and silicate resin were compared referring to their strength behavior in grouted discontinuities based on direct shear tests. The tests indicated significantly different strength behavior of both grouts irrespective of the selected rock type. Using an application example, the implication of these results is shown.

RESUME:

Pour la stabilisation des massifs rocheux dans l'exploitation souterraine, des coulis d'injection chimiques sont utilises de plus en plus frequemment. La resistance de discontinuites collees avec des polyurethanes et des silicates est comparee à l'aide d'essais de cisaillement. Independamment de la petrographie des echantillons, la resistance des deux materiaux est distinctement differente, L'importance des resultats est montree à l'exemple d'une application.

ZUSAMMENFASSUNG:

Chemische Injektionsmittel kommen untertage immer haufiger mit dem Ziel der Gebirgsverfestigung zum Einsatz. Auf der Basis von direkten Scherversuchen wurden die beiden Injektionsmittel Polyurethanharz und Silikatharz bezueglich ihres Festigkeitsverhaltens auf verklebten Trennflachen einander gegenuebergestellt. Unabhangig von der gewahlten Gesteinsart zeigten die Versuche ein signifikant unterschiedliches Festigkeitsverhalten der beiden Kleberarten auf. An einem Anwendungsbeispiel wird die Bedeutung der Ergebnisse herausgestellt.

1.
INTRODUCTION

Jointed rock masses are dominant in many cases of underground projects. The mechanical property of jointed rock is determined by the strength in the discontinuities. To improve this strength behavior, the use of chemical grouts in underground mining and tunnelling has taken over an important part along with the installation of rock bolts and supporting elements. An investigation has been carried out in order to quantify the effectiveness of chemical grouts for the stabilization of jointed rock masses. The grouts, silicate resin and polyurethane resin with a foam factor of 2–3, have stood the test of the in situ applications. They were tested under loading conditions, which simulated the state of stress underground. Using the stress conditions predominant in rock masses, which show compressive components in all principle directions and may cause shear or compression failure in overstressed zones, the testing methods used in the investigation were direct shear tests on grouted and non-grouted natural joints and uniaxial compression tests on cylindrical specimens made of pure grout. In addition to the type of grout, its hardening time and the rock type to be grouted were varied.

2.
IMPLEMENTATION AND RESULTS OF THE TESTS
2.1
The direct shear test

The shear strength as well as tension strength and compressive strength of jointed rock depends on the size of the tested samples. Shear specimens with a shear plane area of approximately 450 cm2 were used. So it was guaranteed, that the samples included a representative cut of natural joints. For that reason the direct shear test on grouted discontinuities has more evidence on geotechnical problems than the bending test on pure grout, where specimens with a maximum cross-section of 16 cm2 are tested (see DIN 53452 [1988)). It is not possible to draw conclusions from the loading conditions in a bending test to the behavior of the shear strength. The results of direct shear tests can be transferred directly to the property of a non-grouted or grouted rock mass, i.e. underground. The direct shear tests were performed in a machine with a capacity of 500 kN each in normal and in tangential direction and a maximum range of shear displacement of 50 mm. A detailed description of the testing equipment is given in NATAU et al. (1979) and LEICHNITZ (1981).

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