The bond mechanism of grouted cable bolt support in rock is primarily frictional and dilational and is sensitive to grout quality, rock stiffness and stress changes in the rockmass. A model incorporating these parameters has been developed and calibrated to predict ultimate bond strength and bond strength at varying degrees of axial slip of the cable. It has been incorporated into a computer program for use in design.
L'attache du cable cimente d'ancrage est affecte par la friction et I'expansion circulaire et devient sensible à la qualite du coulis de ciment, la raideur de la ruche. Ie degre de la glissade Ie long de I'axe du cable ainsi que Ie changement de la pression dans Ie massif rocheux. Un modèle qui incorpore ses paramètres a ete developper et calibrer pour predire Ie resistance de l'attache du cable.
Der Haftmechanismus von initiierten Kabelanken im Fels ist hauptsachlich auf Reibungs- und Dilatanzkrafte zurueckzufuehren und ist von der Qualitat des Initiiergutes, von Felsmodulus und von Spannungsanderungen im Fels abhangig. Ein Modell zur Bestimmung der Kapazitat von Felsankern wurde entwickelt, kalibriert, und fuer die Ankerbemessung im Bergbau programmiert.
Cable bolts have been used as ground support with success for many years in civil construction. In mining, bulk extraction methods have led to the popularization of cables as a cost effective technique for dilution control in non-entry stopes. Unlike most civil engineering installations, cable support systems in these mining environments can undergo a wide variety of environmental changes during their service life. The major difference between typical civil and open stope mining environments is the stress path affecting the rockmass containing the cables. Whereas most civil excavations are constructed with geometries which attract elevated boundary stresses (compression), the geometries of mining stopes are dictated by ore boundaries and mining method. Large decreases in stress near the boundaries of these openings have been measured (Kaiser and Maloney 1992). These decreases occur during the excavation of the supported stope and during subsequent mining of adjacent ore panels. Cable support systems in typical civil works usually perform according to design since increasing boundary stresses (normal to cables) enhance the frictional resistance of the cable/grout bond. On the other hand, cable bolt bond failure has been observed in mining operations where the rock confinement and grout quality has been shown to be adequate. Many of these failures can be attributed to stress decrease and the resultant loss of frictional bond strength (Kaiser et al. 1992a). Research at the Geomechanics Research Centre (GRC) has resulted in the development of an analytical model for the cable/grout/rock interaction which is capable of predicting bond strength. The key input parameters include rock conditions, grout quality and stress change in the rockmass. The model has been calibrated for seven strand cable using a data base of published laboratory and field pull test data from numerous researchers. It has been incorporated into a user-friendly computer program, CABLEBND, for use in design.
The analytical development of the model has been detailed in previous papers by Kaiser et a1. (1992a) and Yazici et al. (1992). The following discussion briefly outlines the components of the model in qualitative terms. In hard rock environments, cable bond strength is limited by the frictional resistance at the cable/grout interface (Stillborg 1984). GRC's model deals only with this interface. The principal components of the model are shown in Figure 1.a. The value, u 1, refers to the radial displacement or dilation of the cable/grout interface.