2-23 Section 235
235-1 Description
Place suitable material excavated under Sections 225, 226, 230 and 240 in embankments, backfills and earth berms, to conform with the lines, grades and typical cross sections shown in the plans. Fill and compact holes, pits and other depressions when unsuitable material has been removed. Work includes preparation, formation, c ompaction and maintenance of the embankment area as well as the formation of benches in the existing ground with rises less than 60 inches . Surcharges and waiting periods may be required for embankments and retaining walls to minimize and control the effects of settlement on structures, approach slabs, pavements, pipes, utilities, etc. Settlement gauges may be required to monitor settlement a t approximate locations shown in the plans and as directed by the Engineer .
235-2 Materials
Refer to Division 10. Use soil consisting of loose, friable, sandy material free of subsoil admixtures, refuse, stumps, rocks, roots, root mats or other unsatisfactory material. Do not use material that meets AASHTO M 145 for soil classification A -2-5 and A -5 with a PI of less than 8 within 12 inches of the subgrade. Wet, d ry or frozen material may be suitable when dried, wetted or thawed, respectively. Aerate and dry material containing moisture content in excess of what is required to achieve embankment stability and specified density. Waste suitable material only with w ritten authorization. Provide Schedule 40 black steel pipes and couplers with steel or wood bases for settlement gauges. Use steel plates with yield strength of at least 36 ksi and pressure treated wood boards for bases of settlement gauges.
235-3 Construction Methods
Coordinate work with excavation operations in accordance with Article s 107-12 and 225-2.
A.Preparation for Embankment Finish clearing and grubbing wit hin an area in accordance with Section 200 before starting embankment. Remove and waste organic or other unsuitable material unless otherwise directed by the Engineer . Plow mowed sod and leave in place where the height of embankment to be constructed is greater than 6 feet measured under the roadbed. Plow or scarify and break up cleavage planes of all underlying road surfaces. Remove or break up existing pavement in accordance with Section 250. Bench existing slopes steeper than 4:1 measured at right ang les to the roadway. Provide rises of at least 12 inches and no more than 60 inches as embankment is brought up in layers. Provide sufficient width for the operation of placing and compaction equipment. Begin bench cut at the intersection of the original ground and the vertical side of the previous cut. Construct benches greater than 60 inches in height only when shown in the plans. Such benches will be paid in accordance with the contract.
2-24 (B) Embankment Formation
Uniformly spread material in successive, approximately horizontal layers of not more than 10 inches depth, loose measurement, for the full width of the cros s section. Compact each layer in accordance with Subarticle 235 -3(C). Shape embankment surface to properly drain at all times. Route construction equipment uniformly over the full width of the embankment and prevent deep rutting. May construct the first layer of embankments across saturated or unstable material that does not support the weight of hauling equipment, by successively dumpi ng a uniformly distributed layer of a thickness not greater than necessary to support hauling equipment while placing subsequent layers. When placing material in swamp or in water, keep unsuitable surge material in a fluid state or remove to prevent trappi ng in or under embankment. When shown i n the plans or allowed by the contract, form a satisfactory base by end or side dumping in valleys, ravines and at the foot of slopes on side hills. Where embankments are being constructed principally of rock or broke n pavement, place in uniform layers with a maximum depth of 36 inches . Place rock or broken pavement so larger pieces are evenly distributed and are no larger than 36 inches in any dimension. Fill all voids. Place rock or broken pavement lifts at leas t 2 feet below finished subgrade or finished grade whichever is lower. Do not place rock or broken pavement 2 inches or greater in diameter within 12 inches of the subgrade or finished grade whichever is lower. Do not place rock or broken pavement in areas where foundations are to be placed. Place select material where indicated in the contract. Construct the top 6 inches of shoulder and fill slopes with material that meets Article 1019 -2. Construct stabilized embankment when required by the contract. Install pipe culverts as specified in Section 300. Construct subsurface drains adjacent to structures as required by Article 414- 8 for box culverts, except for that portion of the drain located below the elevation of the original ground. Do not disturb existing utilities within the project construction limits until released by the Engineer. Do not place rock or broken pavement in embankment areas where piles or drilled shaft foundations are to be constructed or where underground utilities exist . This requirement shall include , but not be limited to , piles and foundations for structures, metal signal poles, overhead sign structures and high mount lighting.
C.Embankment Compaction Compact each layer for its full width to a density equal to at least 95% of that obtained by compacting a sample of the material in accordance AASHTO T 99 as modified by the Department. Copies of these modified procedures found in the Conventional Density Operator’s Manual are available on the Department’s website. Uniform ly bond all layers to preceding layers. Compact all surfaces on embankment slopes, principally constructed of soil, that are flatter than 1 .5:1 using tracked equipment or other approved methods. Increase or decrease moisture content of the material before compacting to produce the maximum density that will provide a stable grade. Exempt portions of rock embankments that cannot be tested by approved methods, from density requirements.
2-25 (D) Maintenance
Maintain all embankments made under the contract until final acceptance. Construct and maintain adequate drainage of surface runoff to prevent soil erosion. Replace damaged or displaced embankment .
E.Surcharges and Waiting Periods Place surcharges at locations shown in the plans. Unless required otherwise in the contract, surcharge embankments after embankments are constructed to the grade and cross section shown in the plans. Construct surcharges with side slopes as directed, 2:1 (H:V) end slopes outside of surcharge limits and surcharge heights shown in the plans. Place and compact surcharge material in accordance with Subarticles 235 -3(B) and 235-3(C). Construct and maintain adequate drainage of surface runoff to prevent e rosion of surcharge material. Waiting period durations are in accordance with the contract and as directed by the Engineer . Surcharge waiting periods apply to surcharge locations shown in the plans and begin after surcharges are constructed to the height shown in the plans. Unless required otherwise in the contract, bridge waiting periods are required in accordance with the following:
1.Apply to bridge embankments and retaining walls within 100 f eet of end bent and bent locations shown in the plans and
2.Begin after bridge embankments and retaining walls are constructed to the elevations noted in the plans. Unless required otherwise in the contract, embankment waiting periods are required in accordance with the following:
1.Apply to embankment locations shown in the plans and retaining walls for embankments with waiting periods and
2.Begin after embankments and retaini ng walls are constructed to the elevations, grade and cross section shown in the plans. Except for maintaining embankments, do not perform any work on embankments or structures including foundations with waiting periods until waiting periods end unless otherwise approved by the Engineer . Place and compact additional material in accordance with Subarticles 235-3(B) and 235-3(C) to maintain embankment grade elevations during waiting periods. Remove surcharges to the grade and cross section 32 shown in the pla ns after surcharge waiting periods ends .
F.Embankment Monitoring Fabricate and install settlement gauges in accordance with the contract and the Roadway Standard Drawings . Make settlement gauges highly visible so gauges are not disturbed while monitoring settlement. Use only hand operated compaction equipment to compact fill material around gauges. Do not damage settlement gauges. Damaged settlement gauges may require replacement or additional gauges and waiting period extensions as determined by the Engineer. Bring all embankments to the grade and cross section shown in the plans before final inspection and acceptance.
235-4 Tolerances
Finish subgrade surface within ± 0.10 feet from the established grade after it has been graded to a uniform surface.
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 115–117 of 857.