The upper area of the reserve spillway – water intake

The wave pattern on seismic records

On the upper part of emergency spillway the section is presented by a thick layer of morainic loam, filling the buried pre-glacial valley branch, and a layer of bulk soils of a protective dam and its base with thickness up to 16-18 m. In this regard, on the record clearly tracked refracted wave propagating along the surface of bedrock dolomites, the reflected waves from the boundaries in the Devonian sediments and series of intense low velocity and low frequency surface waves.

Shallow seismics and electrometry by the method of electrical tomography on the planned route of Plavinas HPP reserve spillway was performed in combination with geotechnical drilling, cone penetration (CPT) and standard penetration (SPT) tests of soils. Seismic surveys were carried out by methods of reflected, refracted and surface waves using all types of elastic oscillations recorded on seismograms with vertical geophones and obtained with a single 32 or 64-channel geophone line with a step between the channels of 2 m.

Section of predicted values of general deformation module of moraine soils on the axis of the middle part of reserve spillway

Direct calculations of elastic constants of the soil massif – Young’s modulus of elasticity, shear modulus, and Poisson’s coefficient – were performed on the base of longitudinal and transverse wave velocities. Predictive physical-mechanical parameters – soil density, module of deformation, angle of internal friction and specific adhesion was calculated using the known empirical dependences for particular soil types, adjusted by the co-processing of seismic data and cone penetration test data at the area of research.

Graphs of the dependences between the velocity of transverse waves and parameters of cone penetration test obtained at the spillway site

Dependence graph correction between the velocity of transverse waves and the standardized number of impacts N under standard (dynamic) testing in moraine soils

Time sections of reflected longitudinal (a) and transverse (b) wave methods

On separate sites of the seismic profiles to increase accuracy of the lower part of moraine soil section displaying, represented by ridges and coarse rubbly material, profiling performed using horizontal receivers of elastic waves. Transverse wave sections obtained from these records with a greater degree of detail reflected the structure of the moraine sediments lower interval with a capacity up to 10-12 m.