Some features of the excavation of the tuffaceous rocks and preparation of the foundations of structures at the Araks hydroelectric development

Conclusions

The results of excavating the tuffaceous rocks in the foundation of the concrete structures during the construction of the Araks hydro development made it possible to reveal some of their characteristics, including the following:

• 1. The anisotropy of the tuffaceous rocks areally and vertically and the presence in their stratum of interbeds of weaker tuffites greatly hampered obtaining a satisfactory quality of drilling and blasting.

• 2. The excavations in the tuffaceous rocks when the slopes are more than 6–8 m high should be accomplished by means of contour blasting by the preliminary slot-formation method, using a millisecond-delay detonator. The use of this method ensures excavations with given slopes and configuration of the flanks, thus securing their preservation.

• 3. The main drilling operations for contour blasting should be performed by percussive-rotary and rotary rigs of the BMK-4 and BTS-150 types.

• 4. Tuffaceous rocks are subject to surface weathering under variable conditions (wetting and drying of the surface) and very quickly lose strength; and their surface does not provide strong contact with the concrete of the foundation slab. These processes occur especially intensely when the stratum is exposed as a result of excavating the pits. Therefore, during preparation of the foundation, the indicated characteristics of tuffaceous rocks should be taken into account in order to preclude the possibility of disturbing their preservation.