FHWA FP-24Public Domain

Section 209 — Structure Excavation and Backfill

Division 200 — Earthwork|PDF pages 151–156

Description

209.01This work consists of excavating material for the construction of structures, except those specifically designated under Section 208. This work also includes preserving channels, shoring, and bracing, sealing foundations, dewatering, preparing foundations, bedding, and backfilling.

Material

209.02Conform to the following Subsection: Soil and soil- aggregate materials 704.01

Construction Requirements

209.03General. Clear the area of vegetation and obstructions according to Sections 201 and 203. Excavate trenches or foundation pits according to Subsection 208.03. Excavate to foundation grade without disturbing the trench or foundation surface. Foundation grade is the elevation at the bottom of the bedding for installing the structure.

209.04Channel Preservation. Preserve channels according to Subsection 208.04.

209.05Foundation Seal . If foundation seals are necessary, construct a foundation seal according to Subsection 208.06. 209.06 Dewatering. If dewatering is necessary, dewater according to Subsection 208.07.

209.07Foundation Preparation . Excavate unsuitable material if encountered at foundation grade as directed. If a footing is required to be keyed into undisturbed material, prepare foundation and construct footing according to Subsection 208.08(c) . Backfill and compact with foundation fill according to Subsection 208.08(d) .

209.08Bedding for Pipe Culverts. Level the foundation. Place uncompacted bedding material over the foundation in a layer of uniform thickness. Lay 4 inches of bedding for pipes with diameters of 12 to 54 inches. Lay 6 inch es of bedding for pipe with diameters larger than 54 inches. Recess the bedding to receive the joints for pipes with belled joints. Place the culvert on the uncompacted bedding layer and backfill according to Subsection 209.09(b) .

209.09Backfill . Backfill as follows:

(a)General. Place backfill lifts evenly on all sides of the structure. Extend each lift to the limits of the excavation or natural ground. Place backfill in compacted lifts no more than 6 inches in thickness. When using flowable backfill, backfill according to Section 614. Do not place backfill against concrete until 80 percent of the design strength is attained . Compact each lift according to Subsection 208.10.

(b)Pipe culverts. Backfill according to one of t he following:

(1)Pipe culverts. Place and compact common backfill or plastic pipe backfill in evenly balanced lifts on each side of the pipe to a height of 12 inches above the top of the pipe culvert. Complete backfilling to the top of the trench. Place and compact common backfill or plastic pipe backfill in the trench in lifts no more than 6 inches in thickness according to Subsection 209.10.

(2)Pipe culverts with flowable backfill. Place and anchor pipe to prevent floating and movement. Backfill using flowable backfill according to Section 614.

(c)Box culverts and structures other than pipe culverts. Place and grade common backfill in compacted lifts no more than 6 inches in thickness. Compact each lift according to Subsection 208.10.

(d)Structural plate structures. Place and compact common backfill to a height of 12 inches above the top of the structural plate structure. If applicable, complete backfilling and compacting according to Subsection 204.10.

(e)Repair existing pavement areas. Conform to Subsection 418.04.

209.10Compacting. Determine optimum moisture content and maximum dry density according to AASHTO T 99, Method C. Adjust the moisture content of the backfill to a moisture content suitable for compaction. Compact material placed in each lift to at least 95 percent of the maximum density. Determine the in -place density and moisture content according to AASHTO T 310 or other approved test procedures. Do not apply density requirements as measured by AASHTO T 310 to material that cannot be tested or compacted to maximum values determined by AASHTO T 99. For this material, fill the voids around the rocky material in each lift with structural backfill or foundation fill as appropriate. Compact each lift until there is no visible evidence of further consolidation.

209.11Acceptance. See Table 209-1 for sampling, testing, and acceptance requirements. Material for common backfill, bedding material, plastic pipe backfill, and foundation fill will be evaluated under Subsections 106.02 and 106.04, except flowable backfill for bedding or backfill will be evaluat ed under Section 614. Shoring and bracing will be evaluated under Subsections 106.02 and 106.04. Excavation and backfill work will be evaluated under Subsections 106.02 and 106.04. Clearing will be evaluated under Section 201. Removal of obstructions will be evaluated under Section 203.

Measurement and Payment

209.12Do not measure structure excavation and backfill for payment. See Subsection 109.05. Table 209-1 Sampling, Testing, and Acceptance Requirements

Material or

Product

(Subsection) Type of

Acceptance

(Subsection) Characteristic Category Test Methods

Specifications Sampling

Frequency Point of

Sampling Split

Sample Reporting

Time Remarks

Source

Foundation

fill, bedding material, common backfill, plastic pipe backfill(1) (704.01) Measured & tested for conformance (106.04 & 105) Classification − AASHTO M 145 1 per soil type Source of material Yes Before using in work − Gradation − AASHTO T 27 & T 11 " " " " −

Production

Foundation

fill, bedding material, common backfill, plastic pipe backfill (704.01) Measured & tested for conformance (106.04) Moisture - density − AASHTO T 99, Method C(2) 1 per soil type Source of material Yes Before using in work − Density − AASHTO T 310 or other approved procedures 2 per lift(3) In-place No Before placing next lift −

(1)Not required if using Government -furnished source.

(2)At least 5 points per proctor.

(3)When installing culvert pipe the backfill placed on both sides of the pipe is considered to be contained in the same lift when the material is placed to the same elevation on both sides of the culvert, the compactive effort applied to one side of the c ulvert is the same as that applied to the other, and the compactive effort is applied to both sides of the pipe during a single work operation. Section 210. — RESERVED

← Previous§ 208 Next →§ 211

Public Domain: FP-24 (FHWA Federal Lands Highway) is a U.S. government publication and is not subject to copyright. Text extracted from the official source ↗. Figures are served from the eCFR; if one does not load, use the link in its place.