. Bulletin . ions: Trans. 12th Int. Geol. Cong., 1913, Ottawa, °—Bull. 86—15 4 50 ENGINEEEIXG PROBLEMS OF PANAMA CAISTAL. 3. AxQOunt and character of the ground water. 4. Earth tremors set up by earthquakes, blasts, passage of railroadtrains, or other causes. 5. Other factors, as (a) heavy structures contiguous to excava-tions, (h) water freezing in rock openings and wedging off rock masses,(c) variation of barometric pressure, and (d) earth strains from thekneading of tidal pull. INFLUENCE OF CRUSHING AND TENSILE STRENGTH OF THE ROCKS INVOLVED. If a rock has liigh crushing strengt
. Bulletin . ions: Trans. 12th Int. Geol. Cong., 1913, Ottawa, °—Bull. 86—15 4 50 ENGINEEEIXG PROBLEMS OF PANAMA CAISTAL. 3. AxQOunt and character of the ground water. 4. Earth tremors set up by earthquakes, blasts, passage of railroadtrains, or other causes. 5. Other factors, as (a) heavy structures contiguous to excava-tions, (h) water freezing in rock openings and wedging off rock masses,(c) variation of barometric pressure, and (d) earth strains from thekneading of tidal pull. INFLUENCE OF CRUSHING AND TENSILE STRENGTH OF THE ROCKS INVOLVED. If a rock has liigh crushing strength, with few joint or other part-ing planes, the exposed face will stand almost perpendicular, withoutshearing or sUpping, at any height with which we need to have con-cern. If it has high crushing strength in small solid fragments, butis much cut by joints, faults, or bedding planes it will not deform orflow, but will slough off masses from steep places until a certain angle, 000-£00- /oo-so H—a >i. O 100 BOO yJOO <fOO 500 600 70O 600 900 FiGUEE 7.—Ideal cross section to illustrate excavatiou deformations, a, Width of zone of deformation,measured from toe of slope; 6, original surface; c, surface after deformation; d, bottom of excavation beforedeformation caused it to bulge upward; e, toe of slope, intersection of slope and bottom planes; /, crack, orbreak, caused by deformation of basal part of the block shown with perpendicular broken lines. Thecurved lines from /, with arrow, show approximately the chief zone of deformation and the direction ofthe motion. which might be called the angle of repose, is attained. Fissures,faults, or bedding planes that incline toward the excavation andintersect its slopes are planes of weakness and promoters of slides,especially if the bedding planes have shale, hgnite, or other greasyrock partings, or if the fault planes are filled with clay or slipperytalcose material. Even if such partings are horizontal, relativelylight bac
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