Laserfiche WebLink
<br /> <br />. <br /> <br />EM 1110-2-1913 <br />31 Mar 78 <br /> <br />general sample borings are selected based on Phase 1 resu ts. Undis- <br />turbed sample borings are located where data on soil shea strength are <br />most needed. The best procedure is to group the foundati n profiles <br />developed on the basis of geological studies and explo~ation into <br />reaches of similar conditions and then locate undisturbed sample borings <br />so as to define soil properties in critical reaches. <br /> <br />~ <br /> <br />. <br /> <br />b. Depth. Depth of borings along the alignment sho d be at <br />least equal to the height of levee but not less than 10 ft. Boring <br />depths should always be deep enough to provide data for st bility anal- <br />yses of the levee and foundation. This is especially impo tant when the <br />levee is located near the riverbank where borings must pro ide data for <br />stability analyses involving both levee foundation and riv rbank. Where <br />pervious or soft materials are encountered, borings should extend <br />through the permeable material to impervious material or tough the <br />soft material to firm material. Borings at structure loca ions should <br />extend well below invert or foundation elevations and belo the zone of <br />significant influence created by the load. The borings mu t be deep <br />enough to permit analysis of approach and exit channel sta ility and of <br />underseepage conditions at the structure. In borrow areas the depth of <br />exploration should extend several feet beaow the practicab e or allow- <br />able borrow depth or to the groundwater table. If borrow s to be ob- <br />tained from below the groundwater table by dredging or oth r means, <br />borings should be at least 10 ft below the bottom of the p oposed <br />excavation. <br /> <br />. <br /> <br />2-10. Geophysical Exploration. <br /> <br />a. Use of geophysical methods of subsurface explorat <br />pected to increase as a part of foundation exploration for <br />because of the long, relatively narrow areas to be explore <br />creasing cost of borings. Table 2-4 summarizes those geop <br />methods most appropriate to levee exploration. These meth <br />fairly inexpensive means of exploration and are very usef <br />polating between borings which, for reasons of economy, ar <br />fairly wide intervals. Geophysical data must be interpret <br />tion with borings and by qualified experienced personnel 0 <br />information is almost certain to result. Because there ha <br />significant improvements in geophysical instrumentation an <br />tion techniques in recent years, more consideration should <br />their use. <br /> <br />b. Currently available geophysical methods can be bro dly sub- <br />divided into two classes: those accomplished entirely fro the ground <br />surface and those which are accomplished from subsurface bo ings. <br /> <br /> <br />on is ex- <br />levees <br />and the in- <br />sical <br />~ ~ea <br />for inter- <br />spaced at <br />d in conjunc- <br />misleading <br />e been <br />interpreta- <br />e given to <br /> <br />2-6 <br /> <br />. <br />