Advertisement

Mechanische Eigenschaften von Störungen und Verwitterungszonen im Granitgebirge und deren genetische Charakterisierung

  • Ch. Lempp
  • O. Natau
Conference paper

Summary

The Hercynian granites of the Schwarzwald area in southwestern Germany display distinct variations in the amount of disintegration and weathering. Different stages of transition ranging from unweathered rock to cohesionless material can be observed in the same level of erosion. The process of disintegration and weathering is accompanied by a continuous decrease in strength. Several material properties, such as dry-density or porosity (fig. 2, 3), creep behaviour (fig. 4, 5) and elasticity (fig. 5, 6) change in a characteristic manner correlating to the decrease in strength. Non-elastic properties of the granite become dominant during disintegration. The granites of the Schwarzwald area can be classified into six stages of weathering, where each stage is characterized by certain mechanical properties (fig. 7).

This Classification in terms of mechanical properties combines the following parameters: 1. uniaxial peak strength, ßD, 2. dry-density, ρd, 3. strain rate ratio, εlateralaxial, 4. creep strain rate per 2 minutes under one half of the uniaxial peak stress, 5. percentage of peak strain rate, % εBR which depends on uniaxial stress in a nonlinear manner, 6. modulus ratio, Ereloading/E1st loading.

Tentatively the problem of determination of rock mass strength is investigated by the aid of laboratory tests. The results of direct shear tests on natural joints of the granites (fig. 8) were used to estimate a lower limit of the strength of the granitic rock mass. Discontinuities as well in the mineral structure as in the rock mass structure cause a similar effect on the p-wave-velocity (fig. 9). In connection with this result it appears plausible that a disintegrated specimen may react like a jointed rock mass. Accordingly the result of multi-step triaxial tests on rock specimens (fig. 10, 11, 12) were used to define an upper limit of rock mass strength of the Schwarzwald granites. The strength of the gran itic rock mass is also classified depending on the mechanical properties of the rock and its discontinuities (fig. 13).

The decrease in strength and the change in mechanical properties are Chiefly caused by increasing microcrack density, disintegration of miner al structure and increasing porosity. Mineralogical and chemical changes especially formation of phyllosilicates, promote disintegration but in all types of granite in the Schwarzwald area occur conditions of only slight chemical weathering intensity.

Disintegration and decrease in strength are mainly the results of mechanical, tectonic and thermal stresses.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Literatur

  1. Brauns J, Hötzl H, Kast K, Lempp Ch, Metzler F, Smykatz-Kloss W (1984) Verwitterung und Auflockerung, Einführung und Versuch einer Klassifikation. (In diesem Band)Google Scholar
  2. Dearman WR, Irfan TY (1978) Classification and index properties of weath ered coarse-grained granites from South-West-England. 3 Int Congr IAEG Vol 2 See II: 119–130, MadridGoogle Scholar
  3. Dearman WR; Baynes FJ, Irfan TY (1978) Engineering grading of weathered granite. Eng Geol 12 No 4: 345–374, AmsterdamCrossRefGoogle Scholar
  4. DGEG-Arbeitskreis Versuchstechnik im Fels (1979) Empfehlungen für die Versuchstechnik im Fels. Die Bautechnik Nr 56 H 7: 217–228, BerlinGoogle Scholar
  5. Dula WF (1981) Correlation between deformation lame11ae, microfractures macorfractures and in situ stress measurements. White River Uplift, Colorado. Geol Soc Am Bull 92: 37–46, Boulder, ColoradoCrossRefGoogle Scholar
  6. Emmermann R (1977) A petrogenetic model for the origin and evolution of the Hercynian granite series of the Schwarzwald. N Jb Min Abh 128 Nr 3 219–253, StuttgartGoogle Scholar
  7. Haas A, Lempp Ch (1983) Entfestigung von Graniten des Südschwarzwaldes durch Verwitterung. Die Geotechnik 1: 11–18, EssenGoogle Scholar
  8. Irfan TY, Dearman WR (1978) Engineering Classification and index properties of a weathered granite. Bull IAEG 17: 79–90, KrefeldGoogle Scholar
  9. ISRM-Commission (1972) Standardization of laboratory and field tests. Suggested methods of determining the maximal compressive strength of rock materials and the point load strength index. ISRM Empfehlungen, OsloGoogle Scholar
  10. John KW (1969) Festigkeit und Verformbarkeit von druckfesten, regelmäßig geklüfteten Diskontinuen. Veröff d Inst f Bodenmechanik und Felsmechanik der Universität Karlsruhe 37, KarlsruheGoogle Scholar
  11. Lempp Ch (1981) Mechanische und mineralogisch-geochemische Eigenschaften von Granit in verschiedenen Verwitterungszuständen. Ber 3 Nat Tag Ing Geol: 191–200, AnsbachGoogle Scholar
  12. Matthess G (1964) Zur Vergrusung der magmatischen Tiefengesteine des Odenwaldes. Notizbl Hess LA f Bodenforschung 92: 160–178, WiesbadenGoogle Scholar
  13. Natau O, Leichnitz W, Balthasar K (1978) Construction of a Computer controlled direct shear testing machine for investigations on rock discontinuities. Proc 4th Int Congr of ISRM Vol 3: 241–243, MontreuxGoogle Scholar
  14. Natau O, Fröhlich B0, Mutschier Th (1983) Recent developments of the larges-scale triaxial test. Proc 5th Int Congr of ISRM Vol A: 65–74, MelbourneGoogle Scholar
  15. Simmons G, Richter D (1976) Microcracks in rocks. In: Strens RGJ ( 1976 ) The physics and chemistry of minerals and rocks. Wiley and Sons, London, p 105–137Google Scholar
  16. Smykatz-Kloss W, Goebelbecker J (1985) Der chemische Verwitterungsgrad von Gesteinen als Maß für ihre ingenieurgeologische Verwendbarkeit. (In diesem Band)Google Scholar
  17. Wang HF, Simmons G (1978) Microcracks in crystalline rock from 5,3 km depth in the Michigan Basin. J Geophys Res Vol 83 No B12: 5849–5856, Washington DCCrossRefGoogle Scholar
  18. Weber K (1982) Conjugate cleavage and microfractures in sandstones and quarzites. In: Int Conf on Planar and Linear Fabrics of Deformed Rocks. Mitt aus d Geol Inst d ETH Zürich Neue Folge 239a, ZürichGoogle Scholar
  19. Wilhelmy H (1981) Klimamorphologie der Massengesteine. 2. Aufl.: 239 S, WiesbadenGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1985

Authors and Affiliations

  • Ch. Lempp
    • 1
  • O. Natau
    • 1
  1. 1.Lehrstuhl für Felsmechanik, Institut für Bodenmechanik und FelsmechanikUniversität KarlsruheKarlsruhe 1Germany

Personalised recommendations