Admin Order 58-02-25-F - Laserfiche WebLink

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Guidelines for Depth of Borings Area for Investigation Structural Foundation ~arge Structure with ~eparate closely spaced ootings. solated rigid foundation. ~ighways and airfields; pipe lines. Retaining walls. Slope stability. Cuts. Embankments. Boring Depth The depth of borings depends upon the soil profile and the type of feasible foundation. Proceed as follows: (1) If no preliminary soil information is available, start with one or two deep borings to bedrock or to a depth equal to the width of the structure. (2) Analyze the boring results and determine the number and depths of additional borings. Borings should be carried to a depth: 1. below any organic soils, muck, artificial fill, or compressible layer; 2. sufficiently deep for establishing the bottom elevation of foundation (footings, piles, or caissons); and 3. sufficiently deep for checking the possibility of a weaker soil, at a greater depth, which may settle under the sustained load. Extend to a depth where increase in vertical stress for combined foundations is less than 10% of effective overburden stress. Generally all borings should extend to no less than 30 feet below lowest part of the foundation unless rock is encountered at shallower depth. Extend to a depth where increase in vertical stress decreases to 10% of bearing pressure. Generally all borings should extend to no less than 30 feet below lowest part of the foundation unless rock is encountered at shallower depth. Minimum depth of borings is 5 ft below bottom of structure, but should extend below organic soil, muck, artificial fill, or compressible layers such as soft clays and silts. 1. Below organic soil, muck, artificial fill, or compressible layer; 2. deeper than poSSible surface of sliding; and 3. deeper than width of the base of wall. Extend to an elevation below active or potential failure surface and into hard stratum, or tc a depth for which failure is likely because of geometry of cross section. Extend to: 1. below organic soil, muck, artificial fill, or compressible layer; 2. deeper than possible surface of sliding; and 3. depth between % to 1 times base width of narrow cuts. Where cut is above ground water in stable materials, depth of 4 to 8 feet below base may suffice. Where base is below groundwater, determine extent of pervious strata below base. Extend to: 1. below organic soil, muck, artificial fill, or compressible layer, 2. deeper than possible surface of sliding; and 3. depth between % to 1 ~ times horizontal length of side slope in relatively homogeneous foundation. Where soft strata encountered, borings should reach hard materials. Page 20f2