Durchlässigkeits- und Injektionsverhalten aufgelockerter Granite

Summary

Within the present research project investigations were made regarding the groutability of disaggregated granites in the Black Forest, Southwest Germany. For comparison and better interpretation of the results general geological methods as well as hydrogeological, engineering-geological and engineering-geophysical methods were applied. A preliminary step was the characterization of rock mass disaggregation with special regard to its importance for the permeability and water routing. For the registration of the direction of propagation special tracing and permeability tests as well as seif-potential measurements have been carried out. Exact information on the preferred water paths. has been obtained by joint tracing with highly adsorptive dyes (e.g. rhodamine). The application of this method, however, is limited, since the Observation of dyed joint planes requires exposure of the affected rock. To detect permeability anisotropy caused by the joint pattern additional geoelectrical seif-potential measurements proved to be most effective. This method is based on the location of increased flow phenomena thus indicating preferred underground passages. Furthermore, the direction of water propagation can be proved by watergauge observations during water pressure tests.

Water absorption was investigated by numerous water pressure tests after LUGEON in three selected test areas showing all transitional stages from solid rock to granitic gruss. Injection pressure and corresponding flowquantities have been registered synchronously. Due to the resulting p,q-diagrams and due to water-gauge and surface observations it was well possible to identify erosional processes of joint fillings. These phenomena were found in 50% of 128 performed packer tests. Injection pressure has been measured both in water pressure tests and grouting experiments directly in the test section.

The grouting experiments were carried out on the analogy of water pressure tests, i.e. with Single packer in steps from bottom to top by means of a variable adjustable Mohno pump. The quantity measurements were carried out by an automatic dosage reservoir and a magnetic inductive flow meter. The water/cement mixtures were prepared in a colloid mixer (C-Mix). Cement mixtures with W/C factors of 0.6, 0.8, 1.0 and 2.0, each with the addition of 3 percent bentonite, were applied. In all grouting tests an oil shale cement (ÖZ 4 5 F) providing a Blaine index of 6047 (± 124) cm²/g and a grinding size of R = 0.09 mm was used. The rheological parameters of the individual cement mixtures and the Sedimentation behaviour were previously determined under laboratory conditions.

The relatively wide-jointed and unweathered first granite type showed heterogeneous LUGEON values, due to individual, particularly hydraulic active joints with larger widths (0.3 – 2.5 mm). Mean values of water and grout absorption were 21.6 LUGEON and 30.1 kg/m. The mean ränge of cementation was 1.90 m.

The second granite type, characterised by a higher joint density and reduced widths (0.2 – 0.5 mm) presented a slightly more homogeneous distribution of the LUGEON values. Average water absorption was 20.1 LUGEON with a grout take of 15.3 kg/m and a mean ränge of cementation of 1.65 m.

For the third granite type an almost homogeneous distribution of water absorption across the whole tested area was found. Due to weathering processes leading to a granite gruss the joint pattern was almost completely removed. Besides this, the influence of granular disintegration zones and a mylonitized fault were found to be relevant factors for local deviations of the LUGEON values. Here the mean value of water absorption and grout take amount to 11.2 LUGEON and 13.4 kg/m at a mean ränge of cementation of 0.65 m.

By combination of the mentioned hydro- and engineering geological insitu tests with additional engineering geophysical measurements it was possible to obtain relevant parameters permitting a geotechnical Classification of disaggregated granites.