Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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Soldier Rev B
| Application Minimum Number of Exploration Points and Location of Exploration Points Minimum Depth of Exploration Retaining walls on deep foundations soldier pile & lagging walls or cast-in-place walls supported on deep foundations) Minimum one exploration point per wall. For walls > 100 feet in length, exploration points every 100 to 200 feet. For walls with anchors, additional exploration points in the anchorage zone every 100 to 200 feet. Exploration depth should be 1 to 2 times the height of the wall below the base of the wall, and should be deep enough to penetrate through compressible soils (peat, organic soils, soft silt & clay) and a sufficient depth into competent bearing layers such as hard or dense soils or rock. For slope stability applications, explorations should penetrate a sufficient depth below potential or preexisting failure surfaces. Bridge foundations For piers or abutments < 100 feet wide, one exploration point per substructure. For > 100 feet wide, a minimum of two per substructure. In soil, depth should beat least 20 feet below the estimated foundation tip elevation or a minimum of two times the minimum pile/shaft group dimension, whichever is deeper. For foundations bearing on or in rock, a minimum length of 10 feet of rock should be cored (to verify it is not a boulder. For drilled shafts socketed in rock, minimum rock core length should be two times the minimum shaft group dimension or three times the diameter of isolated shafts. The recommendations in Table 3-2 maybe adjusted based on local conditions, knowledge of geology, local practice, and precedent. For example, in highly variable conditions, additional borings maybe warranted. Along retaining walls, borings should be spaced in front of and behind the walls to the extent practical to define conditions for the earth pressures on the rear of the wall and conditions for the lateral resistance available in front of the walls. 34 In rock, geologic knowledge based on local experience should be considered and may take precedence over the recommendations for exploration depths given above. In rock mass that is known to be uniform, free of cavities, voids, weathered zones, etc, it may not be necessary to extend explorations more than a few feet into rock. By contrast, rock masses that are known to include cavities, weak or weathered zones, or other highly variable and potentially adverse conditions, additional explorations and/or additional depth maybe warranted. Other types of structures not addressed in Table 3-2 should be addressed based on local site conditions, availability of subsurface information, and engineering judgment. For example, borings along noise walls are typically more widely spaced than retaining walls. However, noise walls tend to be built along roadways which may have additional boring data for cuts, fills, culverts, or retaining walls that can provide supplemental subsurface information for use in the noise wall foundation design. Similar considerations apply for foundations for sign structures, light posts, etc, except that large cantilever signs and sign bridges may warrant site-specific borings. Download 6.03 Mb. Share with your friends:
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