Concrete Roads
and Their Construction

MECHANICAL DEVICES FOR MAKING ROADS 131 by Pawling and Harnischfeger Co., Milwaukee, Wis., and obtain- able in this country from Gaston, Ltd., is shown in Fig. 81. This machine is a complete portable locomotive crane with a lifting capacity of 1| tons at 30 ft. radius. It is driven by a petrol engine and can travel under its own power at a rate of 1 mile per hour. Drag-line Excavators are chiefly used on sticky soils or for lifting loose materials, but they may also be employed for grading roads of which the material is not too hard. As shown in Fig. 84, this type of excavator has an inverted bucket or dipper suspended from the boom by a rope and, on reaching the ground, this bucket is dragged towards the machine till it reaches the limit of its journey ; it is then lifted, the whole crane is swung round and the contents of the bucket are discharged. By suitably regulating the suspen- sion and drag lines, the bucket may be made to dig itself into the ground to a convenient depth prior to its being drawn along and a cut up to 8 in. deep obtained. The caterpillar wheels are a special feature of the drag-line excavators made by Pawling and Harnischfeger Co. Trench Excavators.—As their name implies, trench excavators are specially designed to make deep, but relatively narrow cuts, chiefly for pipes for water, sewage and gas, and electric conduits. Standard trench excavators are manufactured in various sizes to cut trenches from 12 in. to 7G in. wide and in varying depths to a maximum of 20 ft. at a rate of 6 in. to 40 in. linear per minute, according to the nature of the ground and the size of the machine. Trench excavators are commonly built in two classes, one being known as the wheel type, the other the ladder type exca- vator. Wheel Type Trench Excavators are .suitable for trenches not more than 7 ft. 6 in. deep. They consist essentially of a vertical wheel provided with a series of cutters around its circumference, the wheel being mounted on a strongly trussed steel frame which also carries the oil engine, hoist or conveyor for the excavated material and the oil tanks. The excavator should be provided with a steering gear, so that either right or left-hand curved trenches of any radius may accur- ately be cut, and a grade-control or lifting device should also be provided, so that the trench is cut to the full depth and the bottoni is left at any desired slope or grade. In the wheel excavator (Fig. 83) made by Pawling and Hamischfe^er Co., the excavating