OPEN-CUT TUNNELING METHODS 191 



\vith wood, and have circular wooden seats at their bottoms. 

 Each stairway is covered by a light housing, consisting of a 

 steel framework with a copper covering and an interior wood 

 and tile finish. 



I'. /itif'ifi"tt. --The subway is ventilated by means of ex- 

 haust fans located in seven fan chambers, some of which con- 

 tain two fans, and others only one fan. Each of the fans has a 

 capacity of from 30,000 to 37,000 cu. ft. of air per minute, and 

 is driven by electric motor, taking current from the trolley 

 wires. This system of ventilation has worked satisfactorily. 



Disposal of Rainwater. The rainwater which enters the 

 subway from the inclined entrances, together with that from 

 leakage, is lifted from 12 ft. to 18 ft. by automatic electric 

 pumps to the city sewers. The subway has pump-wells at the 

 Public Garden, at Eliot St, Adams Square, and Haymarket 

 Square. In each of these wells are two vertical submerged 

 centrifugal pumps made entirely of composition metal. In 

 each chamber above, are two electric motors operating the 

 pumps. Each motor is started and stopped according to the 

 height of water by means of a float and an automatic release 

 starting box. The floats are so placed that only one pump 

 is usually brought into use. The other, however, comes into 

 service in case the first pump is out of order or the water 

 Miters more rapidly than one pump can dispose of it In the 

 latter case, both motors continue to run until the same low 

 level has been reached. 



Very little dampness except from atmospheric condensation 

 w to be found on the interior walls or roof of the subway, 

 although numerous discolored patches, caused by dampness and 

 dust, may U- seen on some parts of the walls. Substantially nil 

 of the leakage comes through the small drains in the invert 

 leading from hollows left in the side walla. Careful measure- 

 ment was taken at the end of an unusually wet season to de- 

 termine the actual amount of leakage, and the total amount for 

 the entire subway was found to be about 81 gallons per minute. 



