CHAPTER III. 



Dams Importance of efficient dams in marine works Embankments Timber 

 dams Leakage Sluice-valves in dams Half-timber shooting Grooved-and- 

 tongued piling Excessive thickness of clay puddle Dams subject to rise 

 and fall of tide Leaks due to through-bolts Vibration due to pumping 

 Leaks through clay puddle Laminated walings Dams of single rows of piles 

 Timber shield-dam Iron dams Timber dams on Thames Coffer-dams at 

 middle level, Dublin, Birkenhead, Hull, Pola Dock, Esquimalt, Amsterdam 

 Canal, Portsmouth, Limerick, Chatham, Calais. 



DAMS form very important adjuncts in marine construction, 

 either as a means of shutting the water from a site generally, 

 or for enclosing parts where it is necessary to dry the bottom 

 for the purpose of getting in foundations. Being only a 

 temporary work, the tendency is to push the question of 

 economy ol construction to the extreme. An important dam 

 is always a cause of anxiety, any failure or serious accident may 

 entail the loss, not only of much valuable property, but of many 

 lives. A weakly constructed dam augments these anxieties and 

 dangers, and frequently in the end it is more costly on account 

 of the increased expenditure incurred for maintenance and 

 pumping. 



In moderate depths of water and unlimited room, a dam 

 may consist simply of an embankment of clay or other suitable 

 material free from foreign matters, such as large stones, roots, 

 etc., that would be likely to give rise to interstices. In forming 

 an embankment on a muddy foreshore, it is best to deposit the 

 material in horizontal layers, by either tipping it from a stage 

 erected over the site, or dropping it from hopper-barges. If 

 deposited from end-tipping waggons, the material is very liable 

 to slide away with the mud which is pushed both forward 

 and laterally by the tip heads. By adopting the method of 

 horizontal deposit, the mass sinks vertically through the soft 

 mud with far less waste of material. 



A heavy material, such as chalk or stone rubble, would sink 



