Building & engineering news . nstrud^ioni del Tunnel TwinPeaks in San Francisco, Cal. Da L. GLICK, Assistente ingegnere, Ufficio di presidenza di ingegneria, San Francisco il Twin Peaks Tunnel, ora in costruzione di R.C. Storrie & Company per la città di San Francisco, avrà un calcestruzzo tubo rivestito K.ouil piedi di lunghezza per doubletrack, un rapido servizio di transito. Questo foro si collegherà dsupporto grande quartiere residenziale nella parte sudoccidentale della città con il principale nella sezione business. Il costo del tunnel è finanziato liy una valutazione riscossa sullato distretti che circonda i due portali. Il valutare- srade del 7 per c

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Building & engineering news . nstrud^ion of the TwinPeaks Tunnel In San Francisco, Cal. By L. GLICK, Assistant Engineer, Bureau of Engineering, San Francisco The Twin Peaks Tunnel, now under construction by R.C. Storrie & Company for the City of San Francisco, willbe a concrete lined tube K.ouil feet in length for doubletrack, rapid transit service. This bore will connect alarge residential district in the southwestern portion ofthe city with the main business section. The tunnel cost is financed liy an assessment levied onthe districts surrounding the two portals. The assess- srade of 7 per cent and affords extensive views of all por-tions of the city and surrounding country. The apijroach to the easterly ix)rlal is .3.)0 feet longand has a grade of .0424. It consists of a cut 29 feet inwidth, betwc^en two parallel reinforced concrete retainingwalls. As the traffic on Market street is growing morecongested it will be only a few years until a subway forraiiid transit will lie necessary under this thoroughfare.. GENERAL PLA/V and PROFILE ment district at the west end contains 4, 000 acres, mostof which is in large holdings, now subdivided into re-stricted resident tracts. This district was assessed from1-Lc to 3 l-2c per square foot—depending on the estimatedbenefit to be derived from the tunnel—for 85 per cent ofthe total estimated cost of the work and necessary landsfor right-of-way. The section about the east portal iswell developed and the assessment district therein is rela-tively small, about 650 acres. In the event of the construction of a subway it will con-nect with the present construction at the Eureka ValleyStation, and the easterly portal of the tunnel and the ap-proach thereto will be used for surface connection. From the easterly portal the tunnel grade is -I-.014 fof adistance of 600 feet and for the succeeding 1, 075 feet thegrade is -I-.02S7 and is then +.0.3 for 6, 70rt feet, from whichsection to the west portal, a distance of 3, 300 feet, thegrade

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