ticable. In general, the interior dimensions of cofferdams shall be such as to give sufficient clearance for the construction of forms and the inspection of their exteriors, and to permit pumping outside of the forms. Cofferdams or cribs which are tilted or moved laterally during the process of sinking shall be righted or enlarged so as to provide the necessary clearance.

When conditions are encountered which, as determined by the Engineer, render it impracticable to dewater the foundation before placing the footing, the Engineer may require the construction of a concrete foundation seal of such dimensions as he may consider necessary, and of such thickness as to resist any possible uplift. The concrete for such seal shall be placed as shown on the plans or directed by the Engineer. The foundation shall then be dewatered and the footing placed. When weighted cribs are employed and the weight is utilized to overcome partially the hydrostatic pressure acting against the bottom of the foundation seal, special anchorage such as dowels or keys shall be provided to transfer the entire weight of the crib to the foundation seal. When a foundation seal is placed under water, the cofferdam shall be vented or ported at low water level as directed.

Cofferdams shall be constructed so as to protect green concrete against damage from sudden rising of the stream and to prevent damage to the foundation by erosion. No timber or bracing shall be left in cofferdams or cribs in such a way as to extend into substructure masonry, without written permission from the Engineer.

Any pumping that may be permitted from the interior of any foundation enclosure shall be done in such a manner as to preclude the possibility of any portion of the concrete materials being carried away. Any pumping required during the placing of concrete, or for a period of at least 24 hours thereafter, shall be done from a suitable sump located outside the concrete forms. Pumping to dewater a sealed cofferdam shall not commence until the seal has set sufficiently to withstand the hydrostatic pressure.

Unless otherwise provided, cofferdams or cribs, with all sheeting and bracing involved therewith, shall be removed by the Contractor after the completion of the substructure. Removal shall be effected in such manner as not to disturb or mar finished masonry.

206.06 Preservation of Channel. Unless otherwise permitted, no excavation shall be made outside of caissons, cribs, cofferdams, or sheet piling, and the natural stream bed adjacent to the structure shall not be disturbed without permission from the Engineer. If any excavation or dredging is made at the site of the structure before caissons, cribs,

or cofferdams are sunk in place, the Contractor shall, after the foundation base is in place, backfill all such excavations to the original ground surface or stream bed with material satisfactory to the Engineer.

206.07 Backfill and Embankments for Structures Other Than Pipe Culverts. Excavated areas around structures shall be backfilled with approved material in horizontal layers, not over 6 inches in depth, to the level of the original ground surface. Each layer shall be moistened or dried as required and thoroughly compacted with mechanical tampers.

In placing backfills or embankment, the material shall be placed simultaneously insofar as possible to approximately the same elevation on both sides of an abutment, pier, or wall. If conditions require placing backfill or embankment appreciably higher on one side than on the opposite side, the additional material on the higher side shall not be placed until permission shall have been given by the Engineer and preferably not until the masonry has been in place 14 days, or until tests made by the laboratory under the supervision of the Engineer establishes that the masonry has attained sufficient strength to withstand any pressure created by the methods used and materials placed without damage or strain beyond a safe factor.

Backfill or embankment shall not be placed behind the walls of concrete culverts or abutments of rigid frame structures until the top slab is placed and cured. Backfill and embankment behind abutments held at the top by the superstructure, and behind the sidewalls of culverts, shall be carried up simultaneously behind opposite abutments or sidewalls.

All embankments adjacent to structures shall be constructed in horizontal layers and compacted as prescribed in subsection 203.10 except that mechanical tampers may be used for the required compaction. Special care shall be taken to prevent any wedging action against the structure and all slopes bounding or within the areas to be filled shall be benched or serrated to prevent wedge action. The placing of embankment and the benching of slopes shall continue in such a manner that at all times there will be a horizontal berm of thoroughly compacted material for a distance at least equal to the height of the abutment or wall to be backfilled against except insofar as undisturbed material obtrudes upon the area.

Adequate provision shall be made for thorough drainage. Broken rock or coarse sand and gravel shall be provided for a drainage filter at weep holes as shown on the plans. 206.08 Bedding, Backfill, and Embankment for Pipe Cul

verts. Bedding, backfill, and embankment for pipe culverts shall be done in accordance with section 603.

Method of Measurement

206.09 Excavation for Structures. The volume of excavation to be paid for will be the number of cubic yards, measured in original position, of material acceptably excavated in conformity with the plans or as directed by the Engineer, but in no case, except as noted, will any of the following volumes be included in the measurement for pay

ment:

(1) The volume outside of vertical planes 18 inches outside of and parallel to (a) the neat lines of footings and (b) the inside walls of pipe and pipe-arch culverts at their widest horizontal dimension.

(2) The volume outside of neat lines of underdrains as shown on the plans, and outside the limits of foundation fill as ordered by the Engineer.

(3) The volume included within the staked limits of the roadway excavation, contiguous channel changes, ditches, etc., for which payment is otherwise provided in the specification. (4) Volume of water or other liquid resulting from construction operations and which can be pumped or drained

away.

(5) The volume of any excavation performed prior to the taking of elevations and measurements of the undisturbed ground.

(6) The volume of any material rehandled, except that where the plans indicate or the Engineer directs the excavation after embankment has been placed and except that when installation of pipe culverts by the imperfect trench method specified in subsection 603.09 is required, the volume of material re-excavated as directed will be included.

(7) The volume of excavation for footings ordered at a depth more than 5 feet below the lowest elevation for such footings shown on the original contract plans, unless the bid schedule contains a pay item for excavation ordered below the elevations shown on the plans for individual footings.

206.10 Excavation for Bridges. The volume of excavation, designated on the plans or in the special provisions as "Bridge Excavation" will be measured as described above but will be kept separate for pay purposes from the excavation for all other structures.

206.11 Foundation Fill. The volume of foundation fill to be paid for will be the number of cubic yards, measured in final position, of the special granular material actually pro

vided and placed below the foundation elevation of structures as specified and directed, complete in place and accepted.

Basis of Payment

206.12 The quantities, determined as provided above will be paid for at the contract unit price per unit of measurement, respectively, for each of the particular pay items listed below that is shown in the bid schedule, which prices and payment will be full compensation for the work prescribed in this section, except as follows.

(1) Any excavation for footings ordered at a depth more than 5 feet below the lowest elevation shown on the original contract plans will be paid for as provided in subsection 104.02, unless a pay item for excavation ordered below plan elevation appears in the bid schedule.

(2) Concrete will be measured and paid for as provided under section 601.

(3) Any roadway or borrow excavation required in excess of the quantity excavated for structures will be measured and paid for as provided under section 203.

(4) Shoring, cribbing, and related work, whenever included as a pay item in the bid schedule, will be paid for at the lump sum bid price in accordance with the following provisions: This work shall include furnishing, constructing, maintaining, and removing any and all shoring, cribbing, cofferdams, caissons, bracing, sheeting, water control, and other operations necessary for the acceptable completion of excavation included in the work of this section, to a depth of 5 feet below the lowest elevation shown on the plans for each separable foundation structure. Extension of this work required for excavation ordered more than 5 feet below plan elevation will be paid for in accordance with the "Changes" and "Differing Site Condition" clauses of SF23-A.

Section 207.-FINISHING ROADBED

Description

207.01 General. This work shall consist of the finishing of the roadbed and shoulders in accordance with these specifications and in reasonably close conformity with the lines, grades, and cross sections shown on the plans or staked by the Engineer. The work shall be performed after the earthwork has been substantially completed and all adjacent drains and structures have been completed and backfilled. When the plans indicate that a base course or surface course is to be placed, the Contractor shall comply with any requirements as to roadbed preparation specified for it.

Construction Requirements

207.02 New Roadbed. After the roadbed has been substantially completed, the full width shall be conditioned by removing any soft or other unstable material that will not compact properly or serve the intended purpose. The resulting areas and all other low sections, holes, or depressions shall be brought to grade with suitable selected material, provided under section 203 or section 305. The entire roadbed shall then be shaped and compacted as provided under section 203. Scarifying, blading, dragging, rolling, or other methods of work shall be performed or used as necessary to provide a thoroughly compacted roadbed shaped to the grades and cross sections shown on the plans.

The finished roadbed shall be continuously maintained in a condition suitable for traffic until the next course, if any, of material is placed or until final completion of the work, as the case may be.

207.03 Shoulders. When the plans provide for the construction of a base and/or surface course and the construction of shoulders using materials from roadway and borrow excavation, the shoulders shall be constructed to line, grade, and cross section as provided in subsection 207.02 above. Where the plans provide that the shoulders shall be constructed of other materials, the shoulders shall be constructed as provided for in the plans and specifications for the other materials.

Completed shoulders shall be true to alinement and grade and shaped in reasonably close conformity with the section shown on the plans. They shall be cleaned of any accumulations, reconditioned as necessary, and maintained until final acceptance.