The various geotechnical characterization of very weak sedimentary rock including determination of the state of initial stress thereof were carried out with the purpose of designing excavated slopes for the Pereira Barreto Canal.
The uniaxial compressive strength was selected as a property index which enabled the establishment of a criterium of rock classification as well as relationships with shear strengths, deformability and Permeability.
The paper deals with the principal geotechnical properties of Bauru sandstone that have been determined during an investigation for the design of Pereira Barreto Canal, located in the west of São Paulo State, Brazil.
Bauru sandstone is a weak sedimentary rock with uniaxial compressive strengths up to 120 kg/cm2 in natural water contents and has apparently very homogeneous texture. With the purpose of defining geotechnical characteristics of the materials, tests were carried out besides conventional laboratory and in situ tests, some newly developed tests which are described In detail in the followings. These tests' results and its interpretation associated with the application problems related to design are presented here With.
Pereira Barreto Canal is pioneer project In Brazil because of its size and purposes. The canal under construction will be 9,000m long, of width varying from 50 to 70 m with trapezoidal form (see Fig. 1) and of 61 m maximum high excavated slope, with total excavation being 18.5 × 106 m3 including 11 × 106 m3 in sandstone.
The project will integrate the Urubupun ga system consisting of the Ilha Solteira and the Jupia hydropower plants in the Pa rana river which are under operation and Três Irmãos hydropower plant to be erected in the Tietê river. By linking the Ilha Solteira reservoir with the Três Irmãos,an increase in the generation potential of the complex will be achieved and permiting inland navigation between the Parana and Tietê basins.
The principal geotechnical properties interfering directly in the designs of the excavated slope, protection of its surface as well as definition of construction procedures such as phreatic table drawdown and, appliction of sandstone to some temporary works as construction materials, are described herewith.
The forces which participate in a slope analysis of a soil mass and a weak rock mass can be divided into two groups: driving forces and resisting forces. The driving forces consists of gravitational force, the state of initial stress in masses, seepage force and dynamic force caused by earthquakes (which don't exist in this particular case).
The state of initial stress in the masses can affect properties of soil mass and probably even weak rock mass whose shear strengths are affected by experienced stress path and/or preconsolidation pressures both invertical and horizontal directions. Furthermore, the state of initial stress can interfere in force equilibrium of the sliding mass in analysis.
The seepage force must be also carefully assessed comparing the velocity of excavation with the phreatic table drawdown speed.
