582 EXPERIMENT STATION RECORD. [Vol.35 



the same way as those on the clay mixture, but only on 6, 12, 24, and 36-in. 

 depths. ... As in the case of clay there was quite a regular increase in the 

 percentage of transmission as the loads varied from 500 to 10,000 lbs. per 

 square foot, the average increase from minimum to maximum being 47 per 

 cent." 



It is generally concluded that " the percentage of transmission increases with 

 increase of load. For depths of earth greater than 2 ft. the percentage of 

 transmission is always less than 20. For eccentric loads the percentage of 

 transmission is always less than 20 when the loading strip is not over any part 

 of the weighing strip." 



Pressure of wet concrete on the sides of column forms, A. B. McDaniel 

 and N. B. Gaevee {Engin. News, 15 {1916), No. 20, pp. 933-936, figs. 5).— Field 

 and laboratory tests made at the University of Illinois are reported. 



The laboratory tests were made on 12- and 20-in. square column forms 12 ft. 

 high made of planks, with ship lap joints. The concrete was a 1:2:4 mixture 

 of standard cement, glacial sand, and crushed limestone. The following con- 

 clusions were drawn : " The lateral pressure increases with the head up to a 

 certain point, after which the pressure remains nearly constant until the pouring 

 ceases. It is probable that, during the early part of the pouring, the concrete 

 is supported by pressure upon the base of the form, and later a considerable 

 part of the concrete is supported by arch-like action on the sides of the form. 

 In this respect the action of green concrete seems to be similar to that of grain, 

 seeds, clean dry sand, etc., in a bin. The lateral pressure in general corre- 

 sponds to hydrostatic pressure for wet concrete. The lateral pressure increases 

 with the rate of pouring and the degree of wetness and of the consistency. 

 The lateral pressure is about the same for column forms up to 20 in. square." 



The field tests were conducted on a reinforced concrete arch highway bridge. 

 " The tests were made on the spandrel posts of the longer spans. These posts 

 have a cross section of 23 by 30 in. and a maximum height of about 15 ft. They 

 have both vertical and horizontal reinforcing bars." The concrete was a 1:2:4 

 mixture of cement, sand, and gravel. It was found " that the pressure grad- 

 ually increases with the head until a maximum is reached, after which the 

 pressure falls off. The height at which this maximum pressure occurs depends 

 upon the consistency of the concrete and upon the rate of pouring. The actual 

 pressures recorded approximate very closely that of a liquid having the same 

 weight as the concrete, or about 145 lbs. per square foot per foot of head. 



" The results obtained from the field tests agree closely with those secured 

 from the laboratory tests. Concrete falling against the forms may result in 

 high lateral pressures due to impact. A value of 145 lbs. per square foot [per 

 foot] of height would be a rational value for lateral pressure to use in the 

 design of forms. The results of these tests are not conclusive, but it is be- 

 lieved that they are sufficiently consistent and accurate to furnish lateral- 

 pressure values which may be used as a basis lor the design of forms under 

 average working conditions." 



Dynamite experiments, B. Bunting (Agr. Bui. Fed. Malay States, 3 {1915), 

 No. 9, pp. 337-341; abs. in U. S. Dept. Com., Com. Rpts., No. 102 (1916), p. 

 Jfl6). — Experiments to test the effect of explosives on the growth of rubber in 

 loam soil overlying a heavy clay are reported. 



" Taking the experiments over a period of one year it [was] observed that 

 whereas the control gave an increase of 21.93 in., the dynamite plat gave an 

 increase of 32.14 in. for every 100 in. of the original girth, or an increase over 

 the control of 10.2 per cent. . , , 



