1839.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



431 



PLAN OF COFFER DAM. 



Figure 1, shewing the third tier of Braces and part of the Locl<. 



IIS/^ 



z.ar 



tremity of the lock, there is to be a pUitforra of well squared stone 2 

 feet ti inches in depth, also the aforesaid grooves and the lock 

 chambers with quoin stones 3 feet long by 2 feet in breadth. Two 

 courses of bond stone are to be built in tlie wing walls and counter- 

 forts, 15 inches thick agreeably to the drawing, the beds to be at right 

 angles from the face of the wall, the curved part of the river wings, 

 and also of the wings into the entrance basin, are to be faced with 

 stone for 20 feet in height, 10 feet in length, and 'A feet in breadth on 

 the bed, laid header and stretcher alternately, the heads not to be less 

 than 2i feet long on the face, by at least 4 feet on the bed, the 

 stretcliers not to be less than 4-J feet long on the face, by at least 2 feet 

 on the bed, the face to be well dressed, and the beds and joints cor- 

 rectly worked, and laid flush in mortar; the backing to be of the same 

 sort of stone, laid flush in mortar, to be in lengths from 3 to 5 feet, and 

 iu breadths suitab e to the thickness of the walls, and of the height of the 

 front courses ; the stones fur the counterforts are to bond into the wall 

 at least 15 inches, and one stune only is to be used in each counter- 

 fort. 



Above the top of the inverted arches, the chamber walls are to be 

 built concave, or of a curvilinear form in its vertical direction in the 

 iront — they are to be 5 feet 3 inches at the level of the lower side of 

 the coping, and the back of the walls being perpendicular, will deter- 



i 



mine the thickness downwards ; there are to be counterforts as shown 

 in the plan and section, tliey are to be founded at li feet above the 

 lowest part of the underside of the inverted arch, and to be carried to 

 within 4 feet 6 inches of the top of the coping, and from the said 4 

 feet t) inches to diminish to nothing at tlie lower side of the coping, 

 all agreeably to the plans and sections. 



The chambers, recesses, and wing walls of the lock are to be coped 

 with the before-mentioned stone 18 inches thick and 4 feet on the bed, 

 and no stone to be less than 4 feet long on the face, but as much larger 

 as can be got, the face of the stones to be well and neatly dresseil, and 

 the upper front edge to be rounded 3 inches, and the back is to be 

 regularly jointed to 4 feet in breadth, the end joints to be made square 

 throughout, and the bottom beds to be solidly laid on the brickwork in 

 good mortar; there iire to be two cast iron dowels inches long and 

 i: inches square in each joint, run in with Farker's cement. 



A puddle of clay and gravel mixed is to be formed at the back of 

 the walls and counterforts 5 feet thick, to be brought up during the 

 progress of building the walls from the ground to 3 feet above high 

 water-mark of a s|)ring tide, this puddle is to be backed up with 

 earth, and laid in layers as before mentioned, to make firm and solid 

 at the back of the walls and on the excavated ground. 



2 



