TRANSACTIONS OF SECTION G. 609 
vise. It is suggested that a fair approximation to the maximum temperature- 
rise can often be obtained by testing for a time equal to, say, 1) times tie 
thermal time constant, deducing the value of this constant from the cooling 
curve, and thence the maximum temperature-rise from the heating curve. 
WEDNESDAY, SHPTEMBER 17. 
The following Papers were read :— 
1. On Landslides accompanied by Upheaval in the Culebra Culling of 
the Panama Canal. By Vauauan Cornisu, D.Sc., F.R.G.S. 
The author visited the Panama Canal works in 1907, 1908, 1910, and 1912. 
Throughout a distance of about three miles between Empire and Culebra, in 
the Culebra Cut, the bottom rock has for four years past bulged up in many 
places to a height of 20 feet and more. The bulging is accompanied or 
followed by subsidence of the bank behind. Both the convex hump below and 
the concave subsidence above are crevassed, but the surface of the ground 
between sometimes remains unbroken. It was unanimously decided by the 
American and European members of the Board of Consulting Engineers 
appointed in 1905 that the sides of the Cut should be given a slope of three 
vertical on two horizontal, and be cut in terraces, and it was considered that they 
would be stable with a depth of excavation of 245 feet at the position of 
“mile 36,’ which is in the section above referred to, where the worst bulgings 
have occurred. At this point the French excavated to a depth of 45 feet on the 
centre line between 1883 and 1889. In the years which followed, the slopes 
suffered little from superficial weathering. The American Commission com- 
menced excavation in 1904, and carried it to a total depth of 65 feet by June 1909, 
by which time upheaval commenced on a small scale. During the twelve months 
ending June 30, 1910, the bottom was lowered a further 35 feet to a total depth 
of 100 feet, and the terraces were cut away, a continuous slope being substituted. 
Bulging of the bottom and collapse of the sides occurred on a great scale through- 
out this year. During the next year, ending June 30, 1911, the slopes were much 
flattened, and were again cut into terraces, and the blasting charges were reduced. 
Towards the end of the twelve months the upheavals were few and small, but it 
must be observed that the lowering during the year amounted to only 15 feet. 
The next year, ending June 30, 1912, was that of the author’s latest inspection of 
the Cut. During this time the smaller blasting charges were used, the terraced 
form of side was maintained, and the work was favoured by dry weather, and the 
general slope had been reduced to about one vertical on three horizontal. The 
lowering of the bottom by a further 33 feet to a total depth of 148 feet was, 
however, accompanied by a renewal of upheavals on a large scale. The evidence 
is that they occur owing to the crushing and dry flow of thin strata, or seams, 
of weak rock—c.g., lignite—underlying the bottom. The question is: Why was 
not this foreseen either by engineers or geologists, although numerous borings 
had been made and the country geologically surveyed? The author is of opinion 
that the mistake was mainly due to disregard of chemical considerations. The 
cutting here is through horizontally bedded rocks composed of fragments ejected 
from a volcano and deposited in a shallow sea in Tertiary times. Some of the 
strata, or seams, disintegrate rapidly under the physical, and, more particularly, 
the chemical action of rainwater; to which they are now for the first time 
exposed. With such disintegration going on a collapse of the banks would 
necessarily occur, but the frequent occurrence of large upheavals of the bottom 
is due, in the author’s opinion, to stratification. 
The process occurs even under natural conditions. Rocks occur in beds which 
are very thin in proportion to their extent, and are therefore easily deformed if 
unequally supported. When the material of a lower stratum has any degree of 
fluidity, and the pressure upon it is different at different places, there is a flow 
from the place of greater to that of less pressure, and the superincumbent rock 
is let down in the former and bulged up in the latter place. 
1913, RR 
