Foundation Engineering, Inc.Professional Geotechnical Services COMMON ROCK DESCRIPTION TERMS <br />EXPLORATION LOG KEY <br />Rock Quality Designation (RQD) is thecumulative length of intact rock core pieces 4 <br />inches or longer (excluding breaks caused bydrilling and handling) divided by run length,expressed as a percentage. <br />Explanation of Common Terms Used in Rock Descriptions <br />Field Identification UCS (psi) Strength <br />Hardness <br />(ODOT) <br />Indented by thumbnail.R0 < 100 <br />Extremely Weak Extremely Soft <br />Crumbles under firm blows with geological hammer. <br />Can be peeled by a pocket knife.R1 100 - 1,000 Very Weak Very Soft <br />Can be peeled by a pocket knife with difficulty, shallow indentations <br />made by firm blow with geological hammer.R2 1,000 - 4,000 Weak Soft <br />Cannot be scraped or peeled with a pocket knife, specimen can be <br />fractured with a single blow of geological hammer.R3 4,000 - 8,000 Medium Strong Medium Hard <br />Specimen requires more than one blow of geological hammer to <br />fracture it.R4 8,000 - 16,000 Strong Hard <br />Specimen requires many blows of geological hammer to fracture it.R5 > 16,000 Very Strong Very Hard <br />Term (ODOT)Weathering Field Identification <br />Fresh Crystals are bright. Discontinuities may show some minor surface staining. No discoloration in rock fabric. <br />Slightly Weathered Rock mass is generally fresh. Discontinuities are stained and may contain clay. Some discoloration in rock fabric. <br />Moderatedly <br />Weathered <br />Significant portions of rock show discoloration and weathering effects. Crystals are dull and show visible chemical <br />alteration. Discontinuities are stained and may contain secondary mineral deposits. <br />Highly Weathered <br />(Predominately <br />Decomposed) <br />Rock can be excavated with geologist's pick. All discontinuities exhibit secondary mineralization. Complete <br />discoloration of rock fabric. Surface of core is friable and usually pitted due to washing out of highly altered minerals <br />by drilling water. <br />Decomposed Rock mass is completely decomposed. Original rock "fabric" may be evident (relict texture). May be reduced to soil <br />with hand pressure. <br />Spacing (metric) Spacing (imperial)Spacing Term Bedding/Foliation <br /> < 6 cm < 2 in Very Close Very Thin (Laminated) <br />6 cm - 30 cm 2 in - 1 ft Close Thin <br />30 cm - 90 cm 1 ft - 3 ft Moderately Close Medium <br />90 cm - 3.0 m 3 ft - 10 ft Wide Thick <br />> 3.0 m > 10 ft Very Wide Very Thick (Massive) <br />Vesicle Term Volume <br />Some vesicles 5 - 25% <br />Highly vesicular 25 - 50% <br />Scoriaceous > 50% <br />Stratification Term Description <br />Lamination < 1 cm (0.4 in) thick beds <br />Fissile Preferred break along laminations <br />Parting Preferred break parallel to bedding <br />Foliation Metamorpic layering and segregation of minerals <br />RQD %Designation RQD %Designation <br />0 - 25 Very Poor 75 - 90 Good <br />25 - 50 Poor 90 - 100 Excellent <br />50 - 75 Fair