2-24 SECTIO N 204 – EXCAVATIO N FOR STRUCTURES 204.0 1 DESCRIPTION . This work shall consist of the excavation and backfill or disposal of material removed. All excavation for structures below the designated slope or subgrade line as shown on the Plans shall be included in this work . The work is classified as follows:
a.Trench Ex cavation . Trench excavation shall consist of excavation for the construction of all conduits, culvert headwalls, drop inlets, manholes, catch basins, leaching basins, underdrains, concrete steps, and other minor structures ; excavation for the removal of al l existing drainage structures; exploratory excavation for locating underground utility services or other structures; excavation for new culverts and pipes with a clear span of 4 feet or less ; drainage ditches at the inlet and outlet of drainage structures with a clear span of 4 feet or less ; and any other excavation designated in the Contract to be removed under this item.
1.Trench Excavation of Earth . Trench excavation of earth shall consist of all material excavated within the limits shown in the Contract, except boulders measuring 18 cubic feet or more , solid rock, mortared stone masonry, or concrete . Trench excavation of earth shall include the removal of all existing pipes with a clear span of 4 feet or less , regardless of material.
2.Trench Excavation of Earth, Exploratory . Exploratory trench excavation of earth to locate underground utility services or other structures shall be conducted where directed by the Engineer. The Contractor shall use protective measures during this excavation to avoid damage to any underground service or structure. When necessary, the Contractor shall cooperate with representa tives of the utility companies to avoid damage to the utilities by permitting the utility companies to erect suitable supports, props, shoring, or other means of protection.
3.Trench Excavation of Rock . Trench excavation of rock shall consist of all solid rock in formation, or boulders measuring 18 cubic feet or more, excavated within the limits shown in the Contract. All mortared stone ma sonry and concrete excavated within the above limits, irrespective of the size of its components, shall likewise be considered as rock. 2-25 (b) Structure Excavation . Structure excavation shall c onsist of excavation for the construction of foundations and substructure s of all structures with a clear span of over 4 f eet, pipe culverts and storm sewers of over 4 foot clear span, grade separation structures, retaining walls, cribs, and any other excavation designated to be removed under this Contract item. If temporary bracing, sheeting, or other means of supporting the ex cavation is required, construction drawings shall be submitted in accordance with Subsection 105 .06.
c.Granular Backfill for Structures . Granular backfill for structures shall consist of approved material placed within the limits shown on the Plans or directed by the Engineer. 204.0 2 MATERIALS . Materials shall meet the requirements of the following subsection s: Coarse Aggregate for Concrete ................................ ................................ .................. 704.02 Crushed Gravel for Subbase, Fine Graded ................................ ................................ 704.05( b) Granular Backfill for Structures ................................ ................................ ................. 704.08 Concrete shall have a minimum 28 -day compressive strength of 3,000 psi and shall conform to the requirements of Section 541 . When approved in writing by the Engineer, material meeting the gradation requirements for coarse aggregate for concrete may be substituted for granular backfill for structures under footings. When approved in writing by the Engineer, material meeting the g radation requirements of fine graded crushed gravel for subbase may be substituted for granular backfill for structures. 204.0 3 GENERA L CONSTRUCTIO N REQUIREMENTS . The locations and elevations for excavation shown on the Plans shall be considered as approx imate only. The Engineer may order removal of poor foundation material below the designed elevation and replacement with an approved material. All suitable excess excavated material shall be used in the formation of embankment s, at other locations shown on the Plans, or as directed by the Engineer. The Contractor shall haul and dispose of the material at no additional compensation. Construction drawings shall be submitted in accordance with Subsection 105.06 whenever OSHA or VOSHA regulations require a design by a professional engineer. 2-26 204.0 4 PREPARATIO N OF FOUNDATION . The foundation pits shall be excavated so that the footings are the full lengths and widths shown on the Plans. The footings shall be co nstructed with full horizontal beds. Unless otherwise specified or authorized in writing, foundations shall be constructed in the dry. The site shall be dewatered to or below the footing elevation or lowest elevation of a structural component. The excavati on shall continue to either bedrock or the elevation specified for footings on soil. All loose material shall be removed, and all seams in the rock shall be cleaned out and filled with concrete or as directed by the Engineer. No excavation shall be done be low the elevations shown on the Plans unless authorized in writing by the Engineer. Any material excavated without authority shall be replaced with concrete or as directed by the Engineer at the Contractor’s expense. When the footing is to be constructed o n an excavated surface other than rock, particular care shall be taken not to disturb the bottom of the excavation. No excavation shall be done below the elevations shown on the Plans, unless authorized in writing by the Engineer. Any material excavated without authority shall be replaced with approved backfill and thoroughly compacted in accordance with Subsection 204.05(a) at the Contractor’s expense. When poor foundation material is encou ntered at the designed foundation level, it shall be removed as structure excavation or trench excavation and replaced with granular backfill for structures or other suitable material as shown on the Plans or as directed by the Engineer, and thoroughly com pacted in accordance with Subsection 204.0 5(a). 204.0 5 BACKFILL .
a.General Requirements . All spaces excavated and not occupied by structures or select backfill shall be backfilled with material from excavation, unless otherwise specified. The Contractor shall backfill up to the elevation of existing ground or 2 feet over the pipe, whichever is less, as shown on the Plans or as directed by the Engineer. All backfill material shall be placed in 6 inch maximum (loose measure) horizontal layers, and each lay er shall be thoroughly compacted by means of air or mechanical tampers. Backfill material placed within the limits of trench excavation or structure excavation shall have a maximum stone size less than 3 inches. Compaction by means of hand tamping will not be permitted. 2-27 (b) Backfill of Trenches . Backfill for trenches shall be carried to the upper -most level of the trench or subgrade. No stones or blasted bedrock exceeding 3 inches in diameter shall come in contact with pipes during backfill operations.
c.Backfill of Structures . No backfill material shall be placed against a newly completed s tructure until the concrete has cured for 7 days or until it has obtained 85% of the designed compressive strength, and then only with the permission of the Engineer. Where backfill is to be placed on both sides of a structure, the layers on both sides sha ll be brought up simultaneously and at approximately the same level to avoid unbalanced pressure. Care shall be taken to prevent wedging action against the structure. Evidence of satisfactory compaction of the backfill adjacent to structures will consist o f the attainment of the density required for the adjacent embankment material by testing at least every third layer in accordance with Subsection 203.11(d) . 204.0 6 METHO D OF MEASUREMENT .
a.Trench Excavation . The quantity of Trench Excavation of Earth ; Trench Excavation of Earth, Exploratory ; and Trench Excavation of Rock to be measured for payment will be the actual num ber of cubic yards excavated up to the maximum dimensions as follows:
1.The horizontal dimensions for excavation for culverts and pipes (excluding underdrain and underdrain carrier pipe) shall be the distance between vertical planes 18 inches outside of the interior lines of the culvert or pipe.
2.The horizontal dimensions for drop inlets, manholes, end sections, and other minor structures shall be 18 inches outside the exterior lines of the structure.
3.The width dimensions for underdrain shall be sh own on the Plans.
4.The depth dimension for culverts, pipes, underdrain, drop inlets, manholes, and other minor structures shall be the vertical dimension from the original ground surface or bottom limits of other excavation to the bottom of authorized e xcavation. Unless otherwise specified in the Plans, or directed by the Engineer, limits of excavation shall extend 1 foot below the pipe or structure. 2-28 (5) When culverts, pipes, underdrains, drop inlets, manholes, and other minor structures are in emban kment areas, the natural ground line as cross -sectioned shall be the uppermost level of computation, unless otherwise specified. Vertical measurements will be used for the depth in making computations of trench excavation as follows:
a.100% of the volume for the first 5 feet of vertical depth.
b.150% of the volume below the first 5 feet of vertical depth.
6.When Trench Excavation of Rock and Drilling and Blasting of Solid Rock Subgrade occur at the same location, the quantity of Trench Excavation of Rock will be measured for payment below the subgrade.
7.The quantity of any material that the Engineer directs to be removed after the embankment s have been placed will be included in the total amount for Trench Excavation.
8.In measuring masonry or concrete as Trench Excavation of Rock, for all openings having cross -sectional areas of 4 square feet or less, the volume will be included as part of the rock. For all openings having cross -sectional are as greater than 4 square feet, the volume will be deducted and not allowed as either Trench Excavation of Rock or Trench Excavation of Earth.
9.The quantity of Trench Excavation of Earth, Exploratory to be measured for payment will be the number of cubic yards of excavation, regardless of depth, for locating underground utility services or other structures where directed by the Engineer.
b.Structure Excavation . The quantity of St ructure Excavation to be measured for payment will be the number of cubic yards measured and computed by average end area method as follows:
1.Vertically . Between the original ground surface or the bottom limits of any other excavation item, whichever is the lower elevation, and the bottom of the structure excavation. Where Common Excavation , Solid Rock Excavation , Unclassified Excavation ; Channel Excavation ; and Structure Excavation occur at the same location, measurement for Channel Excavation will be m ade only below the lower limits of Common Excavation , Solid Rock Excavation, or Unclassified E xcavation , and measurement for Structure Excavation will be made only below the lower limits of Channel Excavation. 2-29 The removal of authorized material below t he elevation of the bottom of the excavation as shown on the Plans will be measured in accordance with Table 204.06A . TABLE 204.06A – STRUCTURE EXCAVATION MULTIPLIERS Vertical Depth (D) Below Bottom of Excavation Indicated on the Plans (feet) Volume of Structure Excavation Multiplied By 0 ≤ D < 1 100% 1 ≤ D < 5 150% 5 ≤ D < 10 450% 10 ≤ D < 15 750% 15 ≤ D Paid as extra work Where a foundation or component of a structure is designed or directed to be placed on bedrock, an average 6 inch maximum allowance for overbreakage will be allowed for measurement. Additional overbreakage shall be at the Contractor’s expense.
2.Horizontally . Between vertical planes 18 inches outside the neat lines of footings, beams, or other structural compon ents, and parallel thereto except for the following:
a.The horizontal measurements of the Structure Excavation for reinforced concrete boxes shall be the overall width of the box, plus 18 inches on each side, and the length of the structure, plus 18 inche s on each end.
b.The horizontal measurements for corrugated plate arches shall be the width of each abutment, plus 18 inches on each side, and the length of the arch, plus 18 inches on each end.
c.The horizontal measurements for pipes and pipe arches hav ing a diameter or span over 48 inches shall be between vertical planes 3 feet outside the exteriors of each side, and the length of the pipes or pipe arches plus 18 inches on each end.
d.When footings are not used, the neat lines shall be the junction line between the new concrete and the old masonry or bedrock.
c.Granular Backfill for Structures . The quantity of Granular Backfill for Structures to be measured for payment will be the number of cubic yards placed in the complete and accepted work within the confines of the limits shown on the Plans or as directed by the Engineer. 2-30 When Coarse Aggregate for Concrete or Crushed Gravel for Subbase, Fine Graded is substituted for Granular Backfill for Structures, it will be measured and paid for as Granular Backfill for Structures. 204.0 7 BASIS OF PAYMENT . The accepted quantities for Trench Excavation, Trench Excavation of Earth, Exploratory, Structure Excavation, and Granular Backfill for Structures will be paid for at the Contract unit pric e per cubic yard for each of the Contract items specified in the Contract. Payment will be full compensation for performing the work specified, including placement and compaction of backfill, disposal or placement in embankment s of all surplus material, an d the cleaning up of the site following completion of construction area s, and for furnishing all labor, material s, tools, equipment , sheeting, bracing, and incidentals necessary to complete the work . Unless otherwise specified, Structure Excavation will include all sheeting, bracing, dewatering, and siltation control, preparing and submitting construction drawings where required, and incidentals necessary for properly constructing, in the dry, a foundation or structural component. All material removed beneath a vertical depth of 15 feet below the bottom of Structure Excavation limits shown on the Plans, or changes in sheeting, bracing, or dewatering necessitated by excavating below the 15-foot limit, will be paid for as extra work . No differentiation will be made in Structure Excavation between the excavation of wet or dry material, earth , gravel, boulders, rock, old masonry, or reinfor ced concrete. When exploratory excavation is conducted exclusively for the purpose of locating existing underground utility services or other structures when directed by the Engineer, the costs of such excavation, regardless of depth, will be paid for at the Contract unit price bid per cubic yard for Trench Excavation of Earth, Exploratory. Payment will be full compensation for all labor, material s, tools, equipment and incidentals necessary to complete the work , including locatin g and protecting existing underground utility services or other structures, and for restoring the work area to the satisfaction of the Engineer. Payment will be made under: Pay Item Pay Unit
204.20 00 Trench Excavation of Earth ................................ ................................ ......Cubic Yard
204.21 00 Trench Excavation of Rock ................................ ................................ ......Cubic Yard
204.22 00 Trench Excavation of Earth, Exploratory (N.A.B.I.) ................................ Cubic Yard
204.25 00 Structure Excavation ................................ ................................ ................. Cubic Yard
204.30 00 Granular Backfill for Structures ................................ ................................ Cubic Ya rd
2-31 SECTION 205 – DRILLING AND BLASTING
205.01 DESCRIPTION . This work shall consist of drilling and blasting of rock, in accordance with these
specifications, the Plans, and as directed by the Engineer.
205.02 DRILLING AND BLASTING OF SOLID ROCK SUBGRADE . Solid rock subgr ade areas shall
be shattered in place to the dimensions shown on the Plans or directed by the Engineer. The area of blasted rock subgrade shall extend sufficiently beyond the beginning and end of cut areas to ensure the shattering of all rock to a depth of 4 feet below the bottom of subbase material elevation. After detonation, any rock protruding above the bottom of subbase shall be removed. When directed by the Engineer, the Contractor shall excavate a trench with conventional earth moving equipment acros s the blasted rock to determine if the rock is sufficiently shattered to a depth of 4 feet below the bottom of subbase. Afterwards, the trench shall be backfilled with the rock removed.
205.03 DRILLING AND BLASTING USING PERIMETER CONTROL . Perimeter contr ol blasting
refers to the use of explosives and blasting accessories in carefully spaced and aligned drill holes to produce a final excavation surface or shear plane in the rock along the specified excavation backslope. These blasting techniques are used t o better distribute the explosive charge to minimize damage, such as fracturing and overbreak, backbreak, or endbreak, beyond the final excavation face. This is accomplished by using small diameter, decoupled charges in closely spaced blastholes placed on the perimeter of an excavation. Perimeter control blasting methods include line drilling, presplitting, and precision presplitting.
a.Blasting Personnel .
1.Blasting Contractor . The blasting contractor shall be a company specializing in the use of explosives for breaking rock. The blasting contractor shall be responsible for loading and firing each blast, as well as the design and management of blasting operations.
2.Blaster -in-Charge . The blaster -in-charge shall have total authority over the handling , use and security of explosives, and is responsible for coordinating, planning, and supervising explosives use. The blaster -in-charge shall be responsible for inspecting blast areas after each blast event. The blaster -in-charge will be required to be on -site during blasting.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 164–170 of 1,380.