THE HOLLAND TUNNEL — GRAY AND HAQEN 601 



at intervals, and to determine the power losses in bends or elbows 

 in concrete air ducts were conducted at the engineering experiment 

 station at the University of Illinois. 



A concrete model, the linear dimensions of which were one-half 

 those of tlie lower duct of the tunnel, and 300 feet in length was used 

 for direct tests. Outlets with adjustable shutters to control the flow 

 of air were provided at uniform int^irvals on each side. Measure- 

 ments of air velocity and static pressure were made at three locations 

 in the duct, one 5 feet from each end and one midway. Tests were 

 run with all side ports closed and port pockets open at various inter- 

 vals, and with air velocities ranging from 1,000 feet to G,000 feet per 

 minute. A total of 18G blowing tests and 17 exhausting tests were 

 run from which to determine the coellicient of friction. 



On a full-size model of the expansion chamber proposed for tlie 

 tunnel, tests were made to determine the proper shape of the chamber 

 and tiie shape and size of the slot which would give a direction of air 

 flow high enough not to raise dust from the roadway and low enough 

 not to short circuit the fresh air to the inlets into the vitiated air duct 

 over the roadway. These experiments also gave the minimum static 

 pressure required to discharge the requisite quantities of air through 

 the slots at difl'erent locations in the tunnel. A total of 112 tests were 

 made on various shapes of expansion chambers and various widths of 

 slot under the several conditions to be met in the tunnel. 



Experiments on elbows were made in two parts : On galvanized 

 iron single and comj^ound elbows constructed to one-tenth the in- 

 terior dimensions of the elbows to be used in the tunnel, and on con- 

 crete compound elbows to one-half the interior dimensions of those 

 planned for the tunnel ducts. 



To verify under tunnel conditions the amount of carbon monoxide 

 produced by automobiles and the physiological efl'ect of exhaust 

 gases, an experimental tunnel was constructed in the workings of a 

 coal mine at Bruceton, Pa. It was located about 1,000 feet from the 

 entrance to the mine and about 135 feet from the surface. The 

 tunnel had a driveway 8 feet by 9 feet wide, with continuous air 

 ducts above tiie ceiling and below the roadway. It was oval in 

 plan, with a major axis of approximately 135 feet and a minor axis 

 of approximately 110 feet, giving a roadway length of 400 feet. 



Air for He tost was supplied by the mine fan, belt-connected to a 

 steam engine and operated outside the mines. The fan operated 

 normally exhausting, giving upward ventilation in the tunnel. 

 Downward ventilation was accom[)lished by reversing the direction 

 of the air currents through the reversible housing of the fan, which 

 then operated as a blower. 



In the upward ventilation system, air entered the duct under the 

 roadway, passed through adjustable [un-i openings into the con- 



