BRIEF OVERVIEW GEOTECHNICAL APPLICATIONS OF ROCK MECHANICS Part

BRIEF OVERVIEW GEOTECHNICAL APPLICATIONS OF ROCK MECHANICS

Part 1 ROCK DURABILITY AND USE AS DIMENSION STONE

Dimension Stone • Quarried dimension stone has been used as a building material dating to 6000 BC in Jericho • Used extensively for foundations, bridges, aqueducts, road surfacing, and military fortifications

Apennine highway in Italy Tioga Pass near Yosemite Machu Picchu, in Peru One of the most common applications of dimension stone has been construction of gravity retaining walls, usually in mountainous areas with steep bedrock slopes.

• Nimrod’s Castle was built by European Crusaders in the 12 th Century using basalt blocks and limestone • Earthen mounds were often built over tels, or rubble piles, from previous cities or citadels, to gain elevation advantage for defense

• Low porosity crystalline rock, such as granite, has always been desirable because of its superior durability • Massive rocks tend to be less intensely jointed or weathered, but also • Harder to excavate

• Cyclopean masonry rock retaining wall supporting a highway in the Andes Mountains of Peru. Note tunnel at middle right excavated in rock to convey river flow.

RQD • Rock Quality Designation index, or RQD, was introduced by Don Deere in 1963. It judges rock quality based solely on measurements of recovered rock core (above left) in 10 foot increments, based on percent recovery and percentage of the pieces longer than 4 inches.

RQD • RQD = Σ pieces > 4” long (100) total length cored • • • 100 -90 Excellent 90 -75 Good 75 -50 Fair 50 -25 Poor <25 Very poor the reported RQD value varies along the scan line of the recovered core

• The Rock Mass Rating (RMR) System, or Geomechanics Classification, was introduced by Dick Bieniawski in 1972 -73. It has been continually refined, base don case studies of actual excavations.

• “Rock” is a subjective term. Karl Terzaghi arbitrarily defined hard rock as any natural material having qu > 4000 psi, which is same as structural concrete.

• Even the hardest rocks are perturbed by discontinuitities; such as these sheet joints, which are essentially tensile fractures, which form a never ending series of blocks.