211 GEOSYNTHETIC STABILIZED SUBGRADE USING GRADED AGGREGATE BASE
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- Furnish and place a layer of geotextile and 12 in. of graded aggregate base to bridge unstable material and minimize the use of undercutting. Use this item only when specified or directed. In extremely unstable areas, the Engineer may increase the thickness of the graded aggregate base material.
Graded Aggregate Base 901.01 Geotextile for Subgrade Stabilization-Class ST Section 919 Securing Pins or Staples 919.03
- 211.03.01 Test Strip. In extremely unstable areas, the Engineer may direct that a test strip be constructed to determine the thickness of aggregate layer required to stabilize the area. The Engineer will determine the depth of aggregate to be used in the test strip. Construct the test strip at least 100 ft in length and at least one lane wide. The results of the test strip will be used to determine the thickness of aggregate required for subsequent construction.
- 211.03.02 Grade Preparation. Cut the area where the geotextile is to be placed to the depth shown or as directed. Bring the area to the specified line, grade, and cross section. Provide a grade that is smooth as practical and free of debris. Minimize construction traffic on the grade. Remove ruts by reshaping, but do not overwork the grade. Have the grade approved prior to placement of the geotextile. Maintain adequate surface drainage as specified in 208.03.03.
- The Engineer may waive compaction and moisture requirements for the underlying soil.
- 211.03.03 Geotextile Placement. Place geotextile on the prepared surface for the full width of the area to be treated. In areas where longitudinal underdrain is to be placed, place the geotextile up to the edge of the proposed longitudinal underdrain trench, but not where the trench is to be excavated.
- Unroll the geotextile parallel to the base line. Do not drag the geotextile across the grade. Remove wrinkles and folds by stretching and pinning.
- Overlap the geotextile at least 30 in. at roll edges and ends. Overlap the end of the roll in the direction of aggregate placement, with the roll being covered by aggregate on top of the next roll. Pin all roll ends and roll end overlaps a maximum of 5 ft on center. Pin roll edges and roll edge overlaps a maximum of 50 ft on center.
- For curves, fold or cut the geotextile and overlap in the direction of the turn. Pin folds in the geotextile a maximum of 5 ft on center. Immediately repair or replace damaged geotextile as directed. Overlap geotextile patches at least 3 ft into undamaged geotextile.
- Do not allow traffic, including construction equipment, on the bare geotextile.
- 211.03.04 Aggregate Placement. Place the graded aggregate base as specified in Section 501, with the following exceptions:
- (a) Placement and Spreading. Place the graded aggregate base within three working days of geotextile placement. Use the end dumping and spreading method. Place a single lift parallel to the baseline and at the thickness required to provide the specified compacted depth. Keep the turning of construction equipment on the graded aggregate base to a minimum.
- (b) Density Requirements. Immediately after placement, compact the graded aggregate base material to the required density. Unless otherwise directed, compact the top 6 in. to at least 95 percent of maximum dry density within 2 percent optimum moisture. Use T 180 to determine the optimum moisture content and maximum dry density. Use MSMT 350 or MSMT352 to measure the in-place density. Compaction requirements will be waived for the graded aggregate base material below the top 6 in.
- (c) Vibration. Unless otherwise specified or directed, do not vibrate graded aggregate base.
211.04 MEASUREMENT AND PAYMENT
- Geosynthetic Stabilized Subgrade Using Graded Aggregate Base will be measured and paid for at the Contract unit price per cubic yard. The payment will be full compensation for the test strip, and for all material, labor, equipment, tools, and incidentals necessary to complete the work.