jo8 THE IMPROVEMENT OF RIVERS. 



If found necessary triple-lap sheet piling of 2"Xia" plank shall be driven from what 

 is shown on the drawings as the approximate end of the coffer-dam to such point in 

 the hank and to such depth as the Engineer may direct. Sluiceways shall be con- 

 structed as indicated on the drawings. 



13. Details of Construction. The timber and lumber used in the coffer-dam 

 must be sound and sawed to full clinu'iisinns, but may be of any kind. The cribs must 

 be sunk progressively, and as soon as any portion of the excavation is ready. They 

 must be filled to full height with heavy material acceptable to the Engineer, and shall 

 be banked on the outside, as directed by the Engineer, with material not liable to be 

 washed away and subject to the approval of the Engineer; and riprapped where 

 required; and shall be made sufficiently water-tight to prevent objectionable leakage. 

 This filling, banking, and riprapping must be commenced as soon as any portion of 

 the coffer-dam is in place, and must be carried to completion without delay. 



If the contractor so desire, an opening, subject to the approval of the Engineer, 

 may be left temporarily in the down-stream arm of the coffer-dam, to assist the exca- 

 vation. 



(Note. If the coffer-dam is to be of the pile type, the following specification may 

 be substituted. 



The piles may be of any good live timber which can be driven without splitting. 

 They shall be not less than 10 inches across at the small end, and sound and straight. 

 They shall be driven to bed-rock and cut off at given elevations, and must be kept 

 plumb and in line, and at the proper distances apart. After they have been driven 

 they must be dapped and brought to fixed lines for the walings and ties, as shown on 

 the drawings. 



The sheet-piling must be driven close and plumb, and to bed-rock, and be cut off 

 at the proper elevation and spiked to the walings. Obstructions to driving must 

 be removed as far as practicable. 



Sluiceways shall be constructed as indicated on the drawings. 



The ends of the coffer-dam must be securely rooted in the bank, and banked and 

 riprapped as directed.) 



14. Estimates and Payment. All bolts, spikes, and nails used in building any 

 part of the coffer-dam must be supplied by the contractor, and covered in his general 

 price for "Coffer-dam timber." All timber and lumber, including sheet piling, used 

 in the coffer-dam will be classified as "Coffer-dam timber." The timber and lumber 

 will be estimated as the lengths specified on the drawings or required in order 

 to conform thereto, except that no deduction will be made for the parts necessarily 

 cut out in making joints.* All material, except that ordered as riprap, used in filling 



* In some contracts the United States has furnished bills of the lumber and piling to be used 

 in the coffer-dam and elsewhere. In such cases payment is made by the dimensions billed, irrespective 

 of cut-offs. It is advisable, however, where such bills are supplied, to make some provision for payment 

 of material ordered but not used, as circumstances may arise during construction which will modify 

 the amount required. 



