Influence of the water saturation for the strength of volcanic tuffs

Different Hungarian volcanic tuffs (andesite, basalt and rhyolite) were investigated with the goal to determine the influence of the water on their strength. The following petrophysical constants were measured for all the samples both in dry and saturated condition: bulk density, ultrasonic wave velocity, unconfirmed compressive strength (UCS) and Young’s modulus. The destruction work (strain energy) was calculated from the measured stress-strain curves, as well. The influence of the water for the UCS, impedance (scalar of the density and the ultrasonic wave velocity) and the destruction work is shown. In these cases linear relationship can be written between the dry and the saturated constants. Both linear and power equation can be used for the effect of the water on Young’s modulus. Finally the UCS is written as the function of the density and the impedance

Shear failure in rock using different constant normal load

SEILDEL – HABERFIELD’s [1] work was based on the analysis of the regular triangular asperities and assumed that the asperities were rigid. They used normal stiffness shear stress (CNS) to measure the joint dilatation rate and extended the LADANYI – ARCHAMBAULT’s [2] approach. The aim of this research is to investigate the dependence of the constant normal load (CNL) on the rate of the dilatation. Three points were chosen on the bilinear failure envelope: the first in the first linear part, the second in transition stress, and the third in the second part of the bilinear failure envelope. 12 regular triangular cementmortar specimens were used to carry out this research. These cementmortar specimens were investigated by TISA – KOVARI [3] before so all the material and shearing constants were well-known. The other purpose of this research was to observe the influence of the normal stress on the dilatation–displacement curves

Influence of the continuously increasing normal stress to the failure in case of shearing test

In a conventional shearing test the normal force or the normal stiffness is kept constant during the experiment. Sliding under constant normal load occurs in slopes if the environment is not changing during the process. The goal of this paper is to investigate the influence of the continuously changing (i.e. increasing) normal load for the increasing shearing load. Regular triangular cement mortar specimens were used to carry out this research. Both the geometry of the specimens and the mechanical constants were well-known. The "Continuous Failure State" (CFS) shear tests were carried out like the ISRM standardized CFS- triaxial tests, with different starting normal stresses. The differences between the analogous CFS triaxial results are discussed and analyzed. Linear and nonlinear theoretical models are proposed

Shearing tests with continuously increasing normal stress

In the conventional shearing tests the normal force or the normal stiffness are kept constant during the experiment. Sliding under constant normal load occurs in slopes if the environment is not changing during the process. The goal of this paper is to investigate the influence of the continuously changing (i.e. increasing) normal load for the continuously increasing shearing load. Cement mortar specimens with triangular teeth that have the same inclination (regular triangular teeth) were used to carry out this research. Both the geometry of the specimens and the mechanical constants were well-known. The "Continuous Failure State" (CFS) shear tests were carried out according to CFS-triaxial tests, with different starting normal stresses. According to the investigations, the behaviour of the material in case of CFS-shearing tests was always different as in case of CFS-triaxial tests. Linear and nonlinear theoretical models are proposed for the measured curves

Second law of thermodynamics and the failure of rock materials

The relation of nonequilibrium thermodynamics to some failure and fracture theories of rock mechanics is investigated. The basic concepts are given to connect failure to the properties of material equations describing the elastic properties. The resulted in thermodynamic conditions are proved to be compatible with classical localization and failure theories of solid materials. Compatibility with experiments and some empirical, adhoc failure criteria of rocks is also demonstrated

A kőzettest mechanikai állandóinak változása a kőzet állapotának és tagoltsági rendszerének függvényében = Influence of the changing of the rock and fault quality for the rock mass mechanical parameters

Jelenleg számos vonalas létesítményt terveznek Magyarországon, melyek megépítéséhez jelentős kőzetmechanikai, mérnökgeológiai ismeretekre is szükség van. A leggyakrabban használt kőzettest osztályozások nem veszik figyelembe a meglévő diszlokációk várható terjedését, esetleges összekapcsolódásukból adódó új állapotokat, mely jelentős szilárdság-csökkenést okozhatnak. Ezen elméletek hiányossága, hogy a mállás folyamatát sem modellezik. Ez főleg sziklarézsűknél jelentős, mind a tagoló-felületükön, mind a kőzetblokknál. Ugyancsak ezen elméletek a víz hatását csak, mint a tagoló-felületeken befolyó rétegvizet veszi figyelembe, de a kőzet szilárdságváltozásának ebből adódó folyamatát nem (a víz szilárdság csökkentő hatása a nagy porozitású, azaz kisebb szilárdságú kőzeteknél igen jelentős). Megvizsgáltuk eddig a kőzetek szilárdságának változását a víztartalom függvényében különböző porózus kőzeteknél. Kimutattuk, hogy mind a vízzel való telítés hatására, mind a porozitás növekedésével a kőzet szilárdsága exponenciálisan csökken. A csökkenés mértékét az effektív porozitás függvényében ábrázolva általános egyenletet adtunk meg. Egyértelmű összefüggéseket kaptunk a rugalmassági modulus és nyomószilárdság kapcsolata között, mely nem változik a víztartalom hatására. A folyamat megértése és jövőbeli modellezése céljából összefoglaltuk a különböző törésmechanikai elméleteket, a repedések összekapcsolódásának és terjedésének eddigi eredményeit. | Recently, several tunnels are designed or constructed in Hungary, in which good engineering geological and rock mechanics knowledge is necessary. The wieldy used rock mass classification are not investigating the new systems from the crack initiations and coalescence. This new situation is usually decreasing the strength of the rock mass. Lack of these theories is not modeling the influence of the weathering (which is very important in Hungary due to the high values of the temperatures). This should be very important for rock slopes (both the blocks and the joints). They do not investigate the influence of the water for the different petrophysical constituents, neither. In case of high porosity rock the strength decrease rapidly due to increasing the water content. First of all, the influence of the water content for the strength of the rock was investigated in case of different type of highly porosity rocks. A negative exponential relationship was determined between water content and the strength of the rock. Knowing the effective porosity, this equation can be correctly calculated. Secondly, for modeling the crack initiation, propagation and coalescences, the different fracture mechanics models were summarized, in rock mechanical point of view

A módosított Hoek-Brown törési kritérium

A cikk célja a már Magyarországon is bemutatott Hoek-Brown törési elmélet általánosított alakjának hazai bevezetése. Ez az általánosított alak figyelembe veszi a fejtés vagy robbantás alatt bekövetkezõ töredezettségváltozást is. Az elmélet szervesen illeszkedik a Bieniawski féle RMR osztályozáshoz, mivel a Hoek-Brown törési elméletben használt Geológiai Szilárdsági Index (GSI) értéke azzal megegyezik. Számos alagút és sziklarézsû vizsgálata alapján Hoek-Brown és a Mohr- Coulomb törési elméletek bizonyos határon beül átszámolhatók, így lehetõség van a kõzettest súrlódási szögének és a kohéziójának az ismeretére is. A gyakorlati tapasztalatok alapján, a Hoek-Brown töréselmélettel a kõzettest törési határállapota jobban felírható, mint az eddigi hagyományos módszerekkel