While designing a concrete dam on the river Striy the flysh rocks which present a sandwich Lype of a sandstone and argillite were under investigation. Interlayer thickness in some flysh packets ranged from some mm up to dozens of sm. In a dam allignment the flysh packets of A, B, C Lypes were mostly met and tihre data are given in Table 1.

(Table in full paper)

The very rock structure shows the possibility of considerable anisotropy of its mechanical properties.

Rock mass fracturing at dam footing was presented by three systems:

  • stratification joints directed to the upstream at the angle of 45°;

  • shear joints directed to the downstream at the angle of 45–50°;

joints norms] to stratification and forming fine block rock structure. All the joints mentioned were of small extension and opening width from the smallest fractures of mm up to some am.

The set of insitu tests was aimed at the determination of indices of deformation and strength rock properties in A,B,C packets by means of concrete test plates under the action of differently directed loads. It was also meant for seismic and acoustic tests (seismic and ultrasonic) in different directions of both - separate rock interlayers in these packets and of the footing as a whole while penetrating into the mass depths.

Test-plate experiments

In the investigation of anisotropy rock deformeability rigid square concrete test plates were concreted to the rock in such away that the application of normal load to the plate could be parallel or normal to stratification.

Test plates used were of 0.5 and I.0 m2 depending upon the block sizes; vertical plate displacement and the rock surface around were measured with the accuracy of up to 0.00I mm.

While determining strain (deformation) modulus parallel and normal to lamination (DS,,; DS1) according to the test dtiat, Formula I. was applied which has been obtained for an isotropic - layer of limitted thickness loaded by local rigid load (Ukhov, Tsytovich, 1970) were: 2b - plate width,∆6 - pra ssure interval for which the value of Ds,, or Ds,. is determined, w - vertial displacement of footing surface points corresponding to the given pressure interval; WH- coefficient taking into account thickness of a deformed layer and coordinates of the point for which settlement of the surface was measured.

Active zone thickness under every plate was determined by the deflection curve configuration of the rock footing surface around the plate and by using ultrazonic measurement data (Ukhov, 1975).

The analysis made of the solution given by V.B. Lapkin (1975) showed that in the case of 0.6<DS1 Ds„<4.0 the error in determination of DS„; DS1 by Formula (I) does not exceed 20 %. For field tests such accuracy is quite acceptable.

Test plate experiments make it possible to investigate only small rock volumes undergoing deformation under the plate. Therefore, due to a scale effcet typical for fissured rocks, the indices obtained, do not characterize deformeability of large areas of a rock mass.

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