A escarificação é um processo de escavação que utiliza um escarificador (ripper) acoplado a um trator de esteiras para remover materiais de resistência intermediária entre solos e rochas duras em serviços de escavação em obras civis e de mineração. Normalmente é realizada em uma gama muito grande de maciços, desde aqueles constituídos por solos endurecidos, até rochas brandas. Esses materiais podem ser classificados como de segunda categoria de escavação. A determinação da escavação desses materiais depende do tipo e potência dos equipamentos utilizados e das características geológico-geotécnicas dos maciços envolvidos. Os equipamentos tem passado por uma evolução muito grande que ampliou a capacidade de escarificação, mesmo envolvendo rochas de resistência mecânica mais elevada É difícil de avaliar o tipo de equipamento mais adequado a ser utilizado e os custos da escarificação, condição esta normalmente ligada as peculiaridades de cada obra. O projeto de escavação leva em conta as características da rocha (genese, mineralogia, granulometria, descontinuidades, resistência, abrasividade etc) e do maciço rochoso (falhas, fraturas, estruturas, heterogeneidade, umidade, grau de alteração etc), que vão determinar o método de escavação mais apropriado (convencional), com escarificador ou a fogo) e os tipos de equipamentos a serem utilizados.

Rippability is an excavation method using a ripper pulled by a tractor to excavate rocks with low resistence in mining and engineering ground preparation. A range of different rock masses are present in these Works, since hard soilsuntil soft rocks. These materials are classified in second category of excavation in engineering works. The evaluation of rippability involves tractor weight and horse-power and geological factors. The technological development increased the usefulness of tractor-mounted ripper and extended the capability of the ripper in rock. Ripper in hard rocks involves high costs and may be not economic. Its difficult to asses the equipments and ripper costs because it has direct relationship with the works peculiarities. Each work (engineering or mining excavation) will dependo n the equipment disposable (or financial resources) the works contractor and the characteristics of the design and the rock masses. The excavation design evaluates rock parameters (rock type, mineral composition, grain size, discontinuities, strenght, abrasiveness, etc) and rock masses parameters (faults, discontinuities, heterogeneity, weathering, etc) that will determine the appropriated excavation method (conventional, ripper or blasting) and the equipments. This assessment will depend on geotechnical parameters surveys that will indicate the essential informations to situate each rock mass in a excavation category.Among the rock masses, the weaks are those who presente the most favorable characteristics for rippability studies, like low uniaxial compressive strength, (situated between 0.5 to 20 MPa). The study of these rock parameters leads to the assessment of the best criteria for rippability. There are a lot rock masses associated with the term weak rock, porous vulcanic, sedimentar and low grade metamorphic rocks and weathering products. These rock masses have a wide geographic ocurrence in brazilian territory associated to sedimentar basins, low grade metamorphic rocks and also on deep wethered products. There are many classification systems that stablish rock mass parameters to indicate rippability. The older ones use seismic velocity charts associated with tractor weight and horse-power, establishing velocity ranges where rock is rippable. However, seismic velocities suggest average behaviour of rock masses without indicating peculiar portions of the with different characteristics.These characteristics are better established with engineering rock mass classifications, that indicates parameters to every portion of the rock mass, letting us know, by information transportation, the characteristics and average behaviour of the materials with importante dispersions. Five engineering rock mass classifications used to estimating rippability are compared here: Franklin (1970), Weaver (1975), Kirsten (1982), Smith (1986) and Singh et al (1986). The better way to assess the rippability of a rock mass is to apply different rock mass classifications and check the ratings eliminating doubts related to the behaviour of rock masses. This paper suggest the use of Kirstens rock mass classification to hard rock and Smiths (op.cit) and Singhs et al (op.cit) to oow resistance rock. These rock mass classifications show good results in evaluation of rippability, sometimes making adaptations to the rock mass conditions.