and motors. In pumping the suspended sand materials through the system, 

 a considerable maintenance problem is encountered in that the abrasive 

 action of the sand is continually cutting the impeller, the liners and 

 the pump casing to a dangerous degree. Once each 7 to 10 days it is 

 necessary to overhaul the sand pumps and build up the impeller and case 

 for satisfactory operation. (300,000 to 440,000 cubic yards) 



At the end of the discharge line, the line branches into two sections 

 with gate valves before and after each branch. In laying a section of 

 beach, the outboard line or sea line is opened up first and a small 

 "peninsula" is formed along the beach edge. When the sand flow has sloped 

 to the previous fill, the outboard line is shut off and the inboard line 

 is opened to fill the section between the "peninsula" and the shore. 

 The discharge is equipped with a spoon-shaped fitting which flares the 

 material out over a wide area, thus eliminating the digging and channel 

 forming action which would ordinarily occur. 



II. PLANT OPERATION AND DATA 



A study of plant operation can be stated only in generalities; 

 accurate data of actual plant operating time, breakdowns, and the daily 

 or weekly quantities of sand moved are not available. The basis of this 

 study is on a 24-hour day, 6-day week schedule, barring unforeseen break- 

 downs and shutdowns and modification of plant equipment. In general, the 

 sand pumps are repaired on the seventh day of each week by either 

 replacing the liners and impellers or by building them up to obtain 

 additional use. The water pumps do not need any extensive repair, as 

 there is little abrasion or wear on the liners and impellers. Other 

 causes of breakdown are: overheating of electric equipment, breaking of 

 high-pressure lines, and loading of the discharge lines with trash 

 sluiced down by the giants. 



Calculations for any short period would not be accurate, therefore 

 our results are based on monthly sand quantities moved, as furnished by 

 the contractor. These monthly quantities are broken down into hourly 

 quantities, for discussion purposes, and the average result is close to 

 the general plant operation. The month taken for study was December 1947 

 during which best operating results were obtained as conditions were most 

 stable, with a minimum number of breakdowns during the period. Also the 

 actual number of operating days in this period is known. Table 1 indicates 

 the quantity of sand moved each month during the hydraulic excavation 

 period. These quantities were calculated by survey, making cross-sectional 

 charts at the start of operations and at the beginning of each month 

 thereafter, and checking the differences as gross-plant performance. As 

 the terrain is very uneven, actual performance was difficult to determine. 

 However, the contractor's survey and the city survey are within 5 percent 

 of one another. During December (the period of operation was 25 days), 

 1,120,700 cubic yards of material were removed and deposited. It is 

 known that during most of this period, three giants, two eductors and 

 one sluice pipe were in operation. Information from the contractor 



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