BACK FILLING FOR STRUCTURAL EXCAVATION

BACK FILLING FOR STRUCTURAL EXCAVATION

GENERAL
                              Normally structural  back filling allowed minimum 3 days after removed form work and curing
Back fill placed  around the structure shall be same elevation and same time
Back fill shall be placed layer by layer even same moisture content
Without engineer approval no back fill placed
If any special back fill such as around pipe line and retaining wall  not to disturbed levels and alignment

LAYING AND COMPACTION

Back fill placed layer not exceed 150 mm thick and proper compaction

The layer optimum moisture content tolerance ± 2%

Compacted soil with approved compactors.  Generally only plate compactors and vibratory rollers will be allowed for back filling purposes

The compaction shall be done progressively from one side with each succeeding pass uniformly overlapping the previous pass.  The compaction shall continue until each layer is compacted to the degree specified.  

Any area inaccessible to normal compaction equipment shall be compacted by means of mechanical tampers until satisfactory compaction is achieved.

COMPACTION REQUIREMENTS

   The following degree of compaction shall be obtained:

Fills under building foundations, soil rafts	97%	modified proctor
Structural back fill	95%	standard proctor
Fill under ground slabs	97%	standard proctor
Fill under asphalt and paving top layer 250mm	97%	standard proctor
Fill under asphalt and paving lower layers	95%	standard proctor
Non-structural back fill for making up levels in landscaped areas	85%	standard proctor