SOUNDINGS AND HYDRAULIC SURVEYS 19 



tractor to make allowances for this item and roughly estimate the 

 increased quantity to be excavated, after a careful examination of 

 the local conditions of the improvement. In a general way it can be 

 said that this quantity is always less than 10 per cent of the total 

 amount of the excavation. 



Better known is the increase in volume of the excavated material, 

 which has to be transported to the dumping place and for which 

 no compensation will be given, hence the expenses of transportation 

 of this large quantity of material should be included in the cost 

 of excavation. Writing from the experience gained with the United 

 States sea-going hydraulic hopper dredges Manhattan and Atlantic, 

 employed upon the Ambrose Channel in New York Harbor, Mr. 

 Henry N. Babcock says that each dredge was provided with two 

 almost equal sandbins, both carrying together when fully loaded 

 about 2300 cu.yds. But ordinarily a dredge would take in a load 

 of 2200 cu.yds., approximately 1800 yds. in place. Thus according 

 to the experience of the U. S. Engineers in the Ambrose Channel 

 the increase of volume was estimated at 400 cu.yds. per each load 

 of 2220, or in other words it was noticed a difference of 22 per cent 

 between the material measured in place and in the hoppers of the 

 dredges. The total amount of the excavation required by the improve- 

 ment of the Ambrose Channel was estimated at 40,000,000 cu.yds. 

 measured in place. Thus it necessitated the transportation of nearly 

 9,000,000 cu.yds. without any compensation. A very expensive 

 item indeed, when it is considered that the transportation of this 

 material was effected by the same steamer dredges which excavated 

 the bottom. This meant they suspended operations and steamed 

 out to sea, making a trip of nearly 8 miles from shore, to dump 

 their content into deep waters. It took over 400 of these trips 

 to dispose of the increased volume of the material, involving as a 

 consequence a very large expenditure. Since the increasing in 

 volume should be always considered by contractors in preparing 

 bids, especially when the material will be measured in place, it 

 will be convenient to consider the increasing of volume at 30 per 

 cent when there are not more definite data. 



Mr. Robinson, in his article on Excavating and Dredging Machin- 

 ery in Engineering Magazine, in regard to the work of the hydraulic 

 dredge J. Israel Tark says: The quantity of work done was ascer- 

 tained by taking the position of the dredge on the first of the month 

 and again on the first of the following month, and measuring the 



