221EXTENSIBLE REINFORCEMENT FOR MSE WALLS

221.1DESCRIPTION—This work is furnishing and installing geogrids for the class specified.

221.2MATERIAL—

substances.

1.a Mechanically Stabilized Earth (MSE) Walls. Provide backfill for MSE walls consisting of AASHTO No. 8 coarse aggregate, Section 703.2, in areas that require free draining material or in areas that are at or below the 100-year flood elevation. For all other areas of MSE walls provide backfill meeting the following requirements:

Sieve Size Percent Passing 1/2 inch 100 No. 40 0-60 No. 200 0-10*

*Determination of the fines conten t (minus No. 200 sieve m aterial) for MSE wall backfill m ust be determined by wash test according to PTM No. 100. This is in addition to PTM No. 616.

Provide backfill meeting the quality requirements of Type C coarse aggregate or better as specified in Section 703.2(a), Table B, except provide materials free of clay lumps, friable particles, coal , and coke. Do not use metallurgical slag or cinders. Provide backfill with a maximum plasticity index (PI) of 3 as determined according to AASHTO T 89 and T 90. Provide backfill materials with a pH between 5.0 and 9.0, determined according to AASHTO T 289. Provide backfill with an angle of internal friction of not less than 34 degrees as determined according to AASHTO T 236 on the backfill sample portion that is finer than the No. 8 sieve. Coarse aggregat e as specified in Section 703.2 does not require testing for angle of internal friction. Prepare the shear strength test sample by substituting material coarser than the No. 8 sieve with material that passes the No. 8 sieve but is retained on the No. 10 sieve. The percentage of material finer than the No. 10 sieve must remain as proportioned in the original sample before substitution. Shear testing may be performed on samples containing material larger than the No. 8 sieve if the shear device according to AASHTO T 236, Sections 5.4 and 5.5.

coarse aggregate, or PennDOT No. 2A coarse aggregate, Section 703.2, and as specified or indicated.

221.3CONSTRUCTION—As shown on the Standard Drawings, as indicated or specified, and as follows:

and areas indicated. Provide overlaps as specified. Place geogrids flat and free of wrinkles, stretching and anchoring as necessary. Do not allow traffic or equipment on the geogrid until it has been covered with one lift (8-inch loose layer) of backfill. Dump backfill of the type specified on top of the geogrid and then blade material across the grid to the required lift thickness. Maximum backfill drop height is 3 feet. If using tracked equipment to spread backfill, do not cross track or make sudden turns that result in deforming or damaging the geogrid. Compact backfill as specified in Section 206.3 or as specified. Reject all geogrids with defects,

tears, punctures, flaws, deterioration, or damage incurred during manufacture, transportation, storage, or installation as determined. Replace damaged geogrid at no additional cost to the Department.

geogrid. Provide clear identification to every roll of geogrid that provides identification of product designation, the manufacturer’s name, lot number, material quantity, and clearly differentiates between rolls of similar geogrid. Protect all geogrid from direct sunlight, ultra-violet rays, temperatures greater than 140F, mud, dirt, dust, and debris.

reinforcement (machine or roll direction). The maximum allowable vertical spacing of geogrid is 2 feet for MSE wall applications and any other reinforcement applications. Overlap adjacent layers of geogrid as indicated or required, but in no case less than 3 inches. For concave wall o r slope faces maintain the minimum overlap for 75% of the length of the geogrid from the wall or slope face edge of the geogrid. Do not splice or overlap geogrids in the primary reinforcement (machine or roll) direction.

level, free of any sharp protrusion or debris. Place a layer of Class 4, Type A geotextile on top of the prepared subgrade before placement of geogrid. Overlap edges of geotextile and geogrid (both machine/roll and cross machine/cross roll directions) a minimum of 1 foot. Maximum vertical spacing of geogrid is 12 inches.

221.4MEASUREMENT AND PAYMENT—

For the class indicated or specified. Any required or incidental overlaps of geogrid are not included in measurement and payment . Only the indicated plan view reinforced area per geogrid layer is included in payment. Backfill used in the installation of geogrid is included in the payment.

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