SPECIFICATIONS FOR BRIDGE CONSTRUCTION SECTION 2 BACKFILL TABLE OF CONTENTS 2.1 General...2-1 2.2 Materials...2-1 2.2.1 Compacted Non-granular Material...2-1 2.2.2 Gravel Material and Crushed Aggregate Material...2-2 2.2.3 Backfill Material Tests...2-3 2.3 Placing...2-5 2.4 Measurement and Payment...2-5 2.4.1 Unit Price Per Cubic Metre...2-5 2.4.2 Lump Sum Price...2-6
2.1 General Backfill shall include material required to fill excavations adjacent to various bridge components or culvert installations. Backfill shall also include the supply and placing of materials necessary for construction of approach fills, roadway embankments, slopes, channel banks, and berms. All materials shall be sourced and supplied by the Contractor. The Contractor shall be responsible for royalties, processing, loading, hauling, placing, compacting, QC testing and any other incidentals required to supply these materials in place. 2.2 Materials All material used for backfill including native material shall be of a quality acceptable to the Consultant and shall be in a thawed state when placing and compacting and be free from rocks, large or frozen lumps, wood, or other unsuitable material. No backfill material will be permitted to be placed on frozen substrate. 2.2.1 Compacted Non-granular Material Compacted non-granular material shall be non-organic soil such as clay. When reviewed and accepted by the Consultant, non-granular material can be substituted with granular material. Material used for the construction of the clay seals shall be highly plastic clay (exhibiting putty-like properties with considerable strength when dry). Material with very high swelling potential such as bentonite clays will not be permitted. When the proposed material characteristics for clay seals are in question the Consultant may require the Contractor to classify the material using Test Method ASTM D2487 - Classification of Soils for Engineering Purposes. Material shall have a minimum Plasticity Index of 40. 2-1
2.2.2 Gravel Material and Crushed Aggregate Material Where Gravel Material or Crushed Aggregate Material is specified, it shall consist of clean sand and gravel, complying with the following requirements: Designation/Class Metric Sieve Size (CGSB 8-GP-2M) *Gravel Material Des 6 Class 80 Crushed Aggregate Material Des 2 Class 40 Crushed Aggregate Material Des 2 Class 25 Sieve Size μm Percent Passing Percent Passing Percent Passing 125 000 -- -- 80 000 100 -- 50 000 55-100 -- 40 000 -- 100 25 000 38-100 70-94 100 20 000 -- -- 82-97 16 000 32-85 55-85 70-94 10 000 -- 44-74 52-79 5 000 32-62 35-64 1 250 -- 17-43 18-43 630 -- 12-34 12-34 315 6-30 8-26 8-26 160 -- 5-18 5-18 80 2-10 2-10 2-10 % fractures by weight (2 faces) N/A 50+ 60+ Plasticity Index NP - 8 NP - 6 NP - 6 L.A. Abrasion Loss Percent Maximum N/A 50 50 *Note: Native Gravel Material may require processing in order to meet the gradation requirements. 2-2
2.2.3 Backfill Material Tests The Contractor shall submit for the Consultant s review two weeks before placing of the granular material, a sieve analysis representing the material to be used at site. The sampling and testing shall have been done no more than 90 days prior to usage, unless otherwise approved by the Consultant. For non-granular material, the source and material shall be approved by the Consultant, two weeks prior to usage. The Contractor shall be responsible for costs associated to carry out the appropriate testing procedures to confirm specification requirements. The Contractor shall use professional engineering services and a qualified testing firm licensed in the Province of Alberta for all quality control work associated with backfilling procedures. The Contractor shall be totally responsible for production of aggregate that meets all the specified requirements. Des 2 Class 25 Crushed Aggregate material can be used where Des 2 Class 40 material has been specified with no cost to the Department. Results of all quality control tests shall be submitted to the Consultant as they become available. Unless otherwise specified, the latest edition of the following standard Alberta Transportation Test methods (ATT) will be used to determine material characteristics. Test methods and minimum frequencies are shown in Table 2.2.3 Quality Control Testing Requirements. 2-3
Table 2.2.3 Quality Control Testing Requirements Aggregates Tests Sieve Analysis Description Standard Minimum Frequency 1. Crushed Aggregate ATT-25 or ATT-26 One per Source 2. Gravel Material ATT-25 One per Source Plasticity Index AASHTO T90 When requested by the Consultant Percent Fracture ATT-50 One per Source (crushed aggregate) L.A. Abrasion AASHTO T96 When requested by the Consultant Backfill Tests Moisture Density Tests (Proctor) 1. Crushed Aggregate ASTM D689 One test per source (Des 2 Class 25) 2. Non Granular Material (Soil) ASTM D689 One test for each significant soil type Density of Materials (In-place) 1. Crushed Aggregate (Des 2 Class 25) ASTM D2922 Three tests on Culvert Bedding taken at invert level 2. Crushed Aggregate (Des 2 Class 40) or Gravel Material ATT 8 or 9 Three tests for every four lifts of backfill * ATT-58A For Culverts, control established on top lift (Control Strip Method) of bedding material at invert level and the first lift of backfill material for each Bridge Component For Culverts, control re-established on each side of culvert at the 1/3 and mid-point of culvert backfill, and the mid-point of backfill for each Bridge Component 3. Non Granular Material (Soil) ASTM D2922 ATT 8 or 9 Monitor for minimum number of passes on all other lifts Embankment - Three tests per 2 m height of embankment, each side One test on clay seal at each end of Culvert * At the Contractor s option, the Control Strip Method can be used for Des 2 Class 25 material. 2-4
2.3 Placing All spaces excavated and not occupied by permanent work shall be backfilled with compacted material up to the elevation indicated on the drawings or determined by the Department and Consultant. Compacted material may also be required in other locations as shown on the drawings or as required by the Department and Consultant. All backfill material, regardless of type shall be placed in layers not exceeding 150 mm in thickness of loose material, and each layer shall be mechanically tamped with pneumatic tampers or the equivalent. The rate of placing the backfill material shall be such that the tamper can compact thoroughly and uniformly. Compaction of Crushed Aggregate (Des 2 Class 25) and Non Granular Material (Soil) shall be a minimum of 95% Proctor density with optimum moisture content. Compaction acceptance of Gravel Material and Crushed Aggregate (Des 2 Class 40) shall be done using the Control Strip Method with a Nuclear Gauge. On projects where Control Strips are being established, compaction equipment proposed by the Contractor must be reviewed and accepted by the Consultant. Backfill material shall not be placed against any concrete abutment, wingwall or culvert until permission has been given by the Consultant, generally not until the concrete has been in place at least 7 days or the compressive strength of the concrete is 75% of the required 28 day strength. Backfill material around culverts and concrete elements shall be placed simultaneously on both sides to the same elevation to avoid unbalanced loading. Special precautions shall be taken to prevent any wedging action against the concrete and the slope bounding the excavation for abutments and wingwalls. The slope shall be altered by stepping to prevent wedge action. Jetting of backfill material behind abutments and wingwalls will not be permitted. The Consultant may carry out quality assurance testing, if the Contractor s compaction methods and procedures are in the Consultant s opinion not meeting the specification requirements. 2.4 Measurement and Payment Payment for Backfill of the type(s) specified will be either at the unit price bid per cubic metre or lump sum price basis. Such price shall include the cost for all labour, material, equipment, and other items of expense that may be necessary for the successful completion of the backfill. Payment will be determined as follows: 2.4.1 Unit Price per Cubic Metre When payment is to be on unit price basis, the quantity to be paid for shall be the volume, in cubic metres, of the compacted, in place backfill incorporated into the work, based on the dimensions/elevations, indicated on the drawings, or as determined by the Department and Consultant. The quantity will be determined by measuring the volume of the excavation. 2-5
2.4.2 Lump Sum Price When payment is to be on lump sum price basis, the lump sum price shall include full payment for the fill of all structural excavations and other areas specified in conformity with the drawings or specifications. When excavations are taken below specified elevations at the Department and Consultant s request, the additional backfill quantity will be paid by a negotiated lump sum price or in accordance with 1.2.25 Extra Work of the General Specifications as determined by the Consultant. 2-6