Festigkeitsuntersuchungen an Gesteinen und an Gesteinsverbänden mit dem Prallhammer nach Schmidt
The objective of this research program was to verify whether the rebound hammer SCHMIDT system is appropriate to furnish index-figures for the valuation of rock strength in situ.
For many years the rebound hammer has been used for testing and Controlling concrete constructions. After a suitable method for field tests had been worked out — the regulations according to DIN 1048 part 2 and 4 had proved to be unsatisfactory in field work — an easy portable coredrilling machine was constructed in order to receive adequate samples for comparative compressive strength tests. It appears that there is a good correlation between the rebound values gained in field work and the results of the uniaxial compressive strength tests. The test result received by rebound measurements is called “Prellhärte” (rebound hardness).
Further examinations were extended to cores. Please note that the cores always are fixed identically for the rebound tests.
Following preliminary tests a portable clamping device was developed. The examinations performed in that way principally provided the same interdependences between rock strength and rebound values as the testing in situ did.
Subsequently, it was tested whether a loss in rock strength resulting from weathering of rock formations can be identified by rebound hammer tests.
Measurement profiles in the Devonian beds of the “Rheinische Schiefergebirge” in the “German Buntsandstein” and in the “Rotliegende” were taken and interpreted. Five measurement points marked in a distance of 20 cm each are combined to one measurement value (1m total).
It turned out that a continuous reduction of the rebound values can be observed from the unweathered to the completely weathered parts in slight-ly jointed, more or less homogeneous rock formations. Even in those cases where the reduction of rock strength leads to an increase in decomposition, the intensity of this process is reflected in the index-figures.
Concerning future proceedings there is the possibility to use these index-figures to classify differently weathered rocks (in Germany DIN 18 300).
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