4816 HARBOR LN 2016-01-01 MF Import

� ,� r.� i .> �9H t.• A �1 : 9 H [/� H �� . K c� �d �1 "�d H'+C . y i� x � Cjf O � O N � 18 ��g �y� �' HH 8 `� f'7 C y �� Z H tn HOV� �` � � � i 's � .�. .� � j , � r - DAVID L. NELSON AND ASSOCIATES, INC. Consulting Enginecring Geology March 20, 1990 Project No. 2890 Page 7 durinq construction. Tt.e thickness of the rock or gravel will be dependent on the material being protected, and its use. Pressures On Subgrade Walls The design lateral earth pressures acting on retainir.g walls are a tunction of the type oE wall (for example, yielding or non-yielding), the method of construction, and the type of soil used behind the wall. For planning purposes for fixed or non-yieldiny walls, we reconmend that the "at rest" condition should be assumed, and that an equivalent fluid pressure of 50 pounds per cubic foot (pcf) be used for design purposes. For yielding Nalls, such as cantilever walls, the "active" condition may be assumed and an equivalenl fluid pressure of 35 pcf be used. To develop the "active" pressure condition, the wall must be allowed to yield about its base a distance oE about 0.001 times its total height. The effect of surcharges, such as traffic or floor loads, should also he cons'dered. For a uniformly distributed load behind the wall, a corresponding uniformly distributed pressure equal to 30 percent or 50 percent of the surcharge should be added to the lateral soil pressure for yieldinq and non- yielding walls, respectively. If filling behind the wall is performed, compaction of backfill within one-half of the wall embedment height behind the wall should be performed with light equipment such that the wall is not adversely stressed. For planning purposes, design for lateral earth pressures acting on foundation walls could be resisted in the native glacial bearing soils by use of a combination of foundation base friction and passive oressure. A base friction coefficient of 0.45 is recommended within the dense glacial till. A passive equivalent fluid pressure of 450 pcf is recommended within the dense glacial till. Where walls a�e located near slopes, the 9round surface in front of the wall should be 1eve1 for a distance of at least 3 times the depth of burial of the footing, to allow the above p�ssive pressures. Otherwise, a reduction of passive pressure will be required. Specific reductions in passive pressure