Tímarit Verkfræðingafélags Íslands - 01.12.1966, Page 51

TlMARIT VFl 1966
75
total length of almost 6000 m. Figure 10 shows
the result of an analysis of the írequency of the
different permeability in the layers which make
up a lava field. It shows clearly that the lower
contact of lava flow is by far the most permeable
but the interbed has the lowest permeability. This
was tested in the postglacial lava fields but there
is every indication that this is a common rule
independent of the over all permeability of the
lava field which decreases rapidly with increasing
age. In the uppermost line of figure 10 the
permeability test is shown in rock which is
mostly between one and two million years old.
Figure 11 shows results from blow count with
the Borro sound which is really nothing but a
small percussion drill designed for overburden
drilling only. The friction angle and indications
of bearing capacity can be obtained from these
diagrams.
The exploration tunnel made 1962 was 258 m
long and was in moraine, massive andesite and
andesitic flow breccia. The diagrams on figure 12
show the progress and time studies connected
with this tunnel.
The damsite is situated on postglacial lava
flows highly permeable and with ground water
level more than 10 m below river level. The
tightening effect of the silt in the river water
will take care of most of the water loss but
where leakage path is shortest a slurry trench
is made for the safety of structures and to de-
crease the loss of water.
The tunnel will be in basalt lava flows usually
densly jointed. It stands though very well be-
cause the columns are so tight together that
movement cannot occur without breaking the
massive rock. The flow breccia at the contacts
is much softer a rock than the basalt but it is
sparsely jointed and stands well in tunnels. It
is though difficult in blasting and needs much
more explosives than the hard basalt.
The power house is founded on tuff and tuff-
rich breccia. Also a set of basaltic dikes is cross-
ing the power house area. The joint pattern has
strong tendency to be parallel to the dikes and
faultzones and the jointfaces are often a little
altered to clayish material which makes it more
problematic than the joints of the basalt even
if it is much closer spaced.
Heimildir.
Skýrslur til raforkumálastjóra flestar fjölritaðar og
fjalla að einhverju leyti um jarðfræði Búrfells.
Guðmundur Kjartansson 1959: Reports to the State
Electricity Authority on the Geology at some
sites for Potential Hydro-Power Developments
in the Thjórsá and the Hvítá River systems
Southern Iceland.
Þorleifur Einarsson 1960: Jarðfræði Búrfellsvirkjunar.
Þorleifur Einarsson and Haukur Tómasson 1962: Búrfell,
General Geology.
Jón Jónsson and Haukur Tómasson 1962: Búrfell, The
Stratigraphy of Sámsstaðamúli.
Harza Engineering Company International 1963 Búrfell
Project, volume II. appendix B, Geology.
Haukur Tómasson 1963: Temperature Measurements in
Drillholes at Búrfell.
Haukur Tómasson 1963: The Layer SMa.
Haukur Tómasson and Elsa G. Vilmundardóttir 1964:
Búrfell Project, The modefied Saetersmoen
Scheme; Appendix: The Geology .........
Aðrar heimildir:
Allan Cox, Richard R. Doell, G. Brent Dalrymple 1965:
Quaternary Paleomagnetic Stratigraphy, úr The
Quaternary of America.
Ian Mc Dougall and F. H. Chamalaun 1967: Geomagnetic
Polarity Scale of Time; Nature, v. 212. No. 5069.
Trausti Einarsson 1962: Upper Tertiary and Pleistocene
Rocks in Iceland, Reykjavík.
Karl Terzaghai 1964: Introduction to Tunnel Geology.
Rock Tunneling with Steel supports, Youngs-
town, Ohio.
G. Sætersmoen 1918: Vandkraften i Thjórsá Elv, Island.
Jakob Björnsson og Haukur Tómasson 1862: Virkjunar-
rannsóknir á vatnasviðum Þjórsár, Hvítár og
Jökulsár á Fjöllum. Ársskýrsla Sambands ís-
lenzkra rafveitna 1962.
Haukur Tómasson 1963: Jarðfræðilegar aðstæður til
virkjunar Þjórsár við Búrfell og Jökulsár á
Fjöllum við Dettifoss. Ársskýrsla Sambands ís-
lenzkra rafveitna 1963.
Haukur Tómasson 1964: Aurburður og lekahætta úr
uppistöðulónum. Tímarit V.F.l.