9.1. SR 01-07-2013 - Laserfiche WebLink

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STANDARD RE COMMENDATIONS FOR UTILITY TRENCH BACKFILLING Clayey and silty soi Is are often difficu It to corn pact,as they may be naturally wet or may become wet due to ground water or surface/rainwaterdurino construction.So i Is wi I I need to be placed within a certain range of water(inoistur0content to attain desired compaction levels. Moisture conditioning to with in th is range can be time consuming,labor intensive, and requires favorable weather. The de�rmeofoompuokm and the soil type used for houkfiU°vhhio open cut uui|�y�onchcsdepends uo�e function u[ the overlying land Surface. Details are uu follows: ROADWAYS Where trenches are located below roadways.we recornmend using inorganic fill and compacting these soils per Mn/DOT Specification 2105.317 1 (Specified Density Method).This specification requires 100%of the Standard Proctor density in the upper one meter SUbgrade zone, and 95% below this.Note that this specification includes moisture content range requirements which are important for proper subgrade stability. Where available soi Is are wet or of poor quality,it may be possible to use the"Quality Compaction Method"(Mn/D0T Specification 2185,3172) for soils below the upper one meter nuhgrude zone if YOU can tolerate some yuhnNcnoo. However,a high level of stability is still important within the upper subgrade zone and recommend that the"Specified Density Method" be used in this upper subgrade area. We caution that if backfill soils in the lower trench area are significantly uuomh|e it may be difficult or even impossible to property compact soils within the upper one meter mubsraduzone.{n\hiy`cuxc,p|o^iugugaoiuxtUefabricdirect|yovortheunstab|exoi|acanuidinoffseoingthoinxmbiU1y. if fill is placed beneath or within the significant zone of influence of a structure(typically a 1:1 lateral oversize zone),the soil type and minimurn cornpaction level will need to be evaluated on an individual basis. Because trenches result in variable fill depths overa short lateral distance,higherthan normal cornpaction levels and/or more favorable(sandy)soil fill types may be needed. If this situation exists.it is it-nportantthat special geotechnical engineering review be perfonned. NON-STRUCTURAL AREAS In grass/ditch areas,backfill soils should be placed in reasonable lift thicknesses and compacted to a ininimuni of 90%of the Standard Proctor density(ASTM:D698)and/or perthe Mn/DOT"Quality Compaction Method."If lower cornpaction levels are attained, more noticeable subsidence at the surface can occur. Stcep or high slopes require special consideration. 0 1 REPO 18(02/0 1) AMERICAN ENGINEERING TESTING, INC.