Show B U M EJ I 1 L M I 1 EDAM FIRM foundation FOR ROADS i alm aim to distribute pressure due to wheels concentrated on surface look to future prepared by th the united states depart ment of agriculture the purposes of a foundation are to ald aid in dasti distributing the pressure due to wheel loads concentrated on the road fond surface so that the intensity of 0 pressure on the will not exceed B n safe unit bearing power and also to prevent it if possible the crust of the rond road from being disturbed by the upward pressure of the all due to the action of frost ground water or other disturbing influence in the case of a pavement consisting 7 of comparatively small blocks such ns is vitrified fied brick bonded to each other very slightly or not at all an entire wheel loud load might be concentrated on only a few a ti ana wa 1 tl 4 s y f tf aar 0 iz 6 o sand and clay road square inches of foundation in which case it would be necessary for the foundation to take tak ecari care rf t practically the entire distribution nt the load on I 1 the other hano hand a monolithic pavement in which the individual units are well bonded together might distribute the wheel loads to obviate till all necessity of further distribution by the foundation and if adequate drainage were provided and there were no danger of leaving beaving of sub grades the foundation might be omitted entirely the heaviest vehicle that ordinarily hns hiis passed over a public highway heretofore Is the 15 ton traction engine such engines are so designed that the rear axle carries carnieg about two thorda of the total weight which arrangement ran gement gives a concentrated pressure on the road surface of about five tons under tinder each rear wheel the use of much heavier equipment Is in sight however and unless some regulations be passed to prohibit it the occurrence of tenton ten ton or even heavier mo tor trucks may become common on highways adjacent to large cities or between large centers that are only a few miles apart in assuming the maximum wheel lond load tor for any particular road a reasonable allowance should be made for future increase since motor trucks have come into use there has been a constant tendency to increase both their rates of speed and the loads they carry and it Is probable that this tendency will continue furthermore many roads not now subjected to motor truck traffic will attract such traffic after they are improved and till this s possibility lity always should be b considered rne increase rease in the of traffic also way may be an important factor |