Three to four groups of standard grouted bolts were installed in different types of rock on the basis of the design parameters, with one or two grouted bolts in each group. Three groups of grouted bolts with 70%, 80%, and 90% mortar filling were tested. The degrees of filling were set as grade A for over 90% filling, grade B for 80-90% filling, grade C for 70-80% filling, and grade D for less than 70% filling. Grades can be set as desired on the basis of the design, with four as the maximum number of grades that can be set for this instrument.
The amplitude of the reflected wave is then determined on these standard grouted bolts, an average value being taken when there is more than one grouted bolt in a group (Fig. 3). These values serve as calibration standards for other grouted bolts. The calibration values are input into the instrument before performing determinations on other grouted bolts. When other determinations are made, the lengths of the grouted bolts and the degree of mortar filling can be displayed automatically by the measuring instrument.
When determinations are to be made on individual grouted bolts, the outside ends of the grouted bolts should first be smoothed (they may be sawed flat) and the pulse generator attached. Then the receiving head of the coupling device is affixed to the outside end of the shaft body.
C
Figure 3
In situ test of the degree of mortar filling.
Water is then poured to fill the inside wall of the coupling apparatus as well as any voids that may exist on the surface of the outside end of the grouting bolt.
The instrument monitors the reflected signal in wave form by means of an oscilloscope. When the operator has manually adjusted the instrument until reflected signals appear, the instrument automatically displays the length of the grouted bolt, the amplitude of the reflected wave, and the degree of mortar filling.
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