From Eng. News-Record, Vol. 82, 1919, p. 740. ] Wheel excavators are not adapted to the excavation of sewer trenches over 3 to 4 feet in width and 6 to 8 feet in depth. The endless-chain excavators are suitable for depths of 25 feet with widths from 22 to 72 inches, and due to the arrangement permitting buckets to be moved sideways they will cut trenches of different widths with the same size buckets. This is an advantage where there are to be irregularities in the width of the trench such as for manholes or changes in size of pipe. With excavating machines pipe can be laid within 3 feet of the moving buckets and the trench backfilled immediately, thus making an appreciable saving in the amount of sheeting. In the construction of trenches for drain tile at Garden Prairie, Illinois, the sheeting was built in the form of a box or shield fastened to the rear of the machine and pulled along after it as is shown in Fig. 91. The performance of this type of excavating machine under suitable conditions is large. A remarkable record was made by Ryan and Co. in Chicago,[82] with an excavating machine. 1338 feet of 32–inch trench were excavated to an average depth of 8½ feet in 7 hours, or an average of 160 cubic yards per hour. More could have been accomplished if it had not been for delays in supplies. Another crew at Greeley, Colorado,[83] with a Buckeye endless-chain ditcher weighing 17 tons and costing $5200, averaged 232 cubic yards per day for 300 days, and the cost was 10.7 cents per cubic yard. A 15–ton Austin excavator can be expected to remove 300 to 500 cubic yards per day. The cost of operation of the machines is made up of items listed in Table 50. The figures given are merely suggestive. TABLE 50 COST OF OPERATING DITCHING MACHINE