EECLAMATIOlSr OF TIDE LANDS. 387 



ravages of the toredo. Such gates are no more expensive than steel 

 and are far more desirable. The gates here recommended are so 

 planned that they can be readily detached from the framework with- 

 out injury to it, if at any time repairs should be necessary. 



Plans and complete drawings for a cheap wooden abutment, with 

 one or more gates, as required, and also plans and drawings for a 

 concrete abutment with creosoted wooden gates are given on page 

 396. This is the most desirable gate that can be constructed, and 

 where sand or shells can be readily procured its cost will be but little 

 more than a wooden abutment serving the same purpose. 



The following general directions for constructing either of these 

 gates will serve as a guide for any locality: 



EXCAVATION. 



The foundation for the abutment should be prepared by excavat- 

 ing the muck and soft material to a firm clay or sand bottom. In 

 order to do this successfully it will be necessary in nearly all cases 

 to drive some form of tongue-and-groove sheet piling, so as to form 

 a tight cofferdam around the proposed pit. A pumping plant of suf- 

 ficient capacity to keep the pit dry at all times must be provided. 

 The abutment may be of timber, as shown on the first set of plans, 

 or it may be of stone, brick, or concrete, as shown on the second set. 

 In case timber is used, the foundation should be brought up to the 

 proper grade by filling in with good clay or a grouting of broken 

 stone and cement mortar. Great precaution must be taken to make 

 the foundation such that water can not find its way under the tim- 

 bers, in which case the earth would be washed out and the value of 

 the structure destroyed. In case a firm foundation can not be secured 

 otherwise, round piling, on which to rest the abutment, should be 

 driven in the pit. In the wooden structure the bottom sills can be 

 secured to the piling by means of drift bolts. This will support the 

 structure so as to prevent settling and the water can be shut off by 

 the sheet piling above and below the abutment. Where broken 

 stone or suitable sand can be readily procured, concrete will be found 

 the most desirable material, and we recommend its use. The desired 

 shape for the masonry may be secured by making forms of lumber 

 which can be removed after the mortar has set. The proper pro- 

 portion of cement and sand to form concrete depends in a measure 

 on the strength of the cement and the quality of the sand used. With 

 any good natural cement and clean, sharp sand a proportion of 1 to 

 5 or even 1 to 7 would make very substantial work. Methods of 

 mixing and tempering mortar for concrete are so well known that 

 it is hardly necessary to explain them here. The things to be insisted 

 upon in any concrete work are fresh cement, clean, sharp sand, 

 plenty of water, thorough mixing, and immediate use. If these are 



