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�• s ._, „- .. •,.�� .- -.•s`-..q�• -ems •-� `i't '.��". '-i a- "cam T. <br /> result of yielding of the reinforcing steel. Therefore, a safety factor of 2 <br /> through an increase is the quantity of reinforcing steel was not made in this <br /> case. Some reinforcing steel is advisable in the downstream side to control <br /> temperature and shrinkage induced stresses. The quantities of steel indicated <br /> by the simple bending analysis do not appear to be excessive for typical <br /> tunsel sizes. . <br /> gulkhead kvtb Based on pjgraulic Pressure , <br /> xydrofracturing, generally referred to as hydrofracing, of sedimentary <br /> formations from drillholes is frequently undertaken for the purpose of <br /> stimulating oil well production. Formation breakdown pressure (1p) is a <br /> t to the <br /> function of (1) the tensile strength of the rock immediatelyia�dja lar o <br /> drilihole, (2) the in situ stress field in the plane perpend <br /> drillbole and (3) the pore pressure pent is the formation. are the <br /> dehoeft <br /> present , et <br /> al (1973) presented a study of bydrofraeing a competent rockfrom �� <br /> driliholes. ' they presented the following well-known equation for breakdown.. <br /> 0 pressure: • <br /> op - Ts +Ants - Smax - Pf (20) <br /> All terms is psi ' <br /> Ts - tensile strength <br /> Smin . alai" stress normal to the,borehole <br /> Smax . maxiom stress normal to the borehole <br /> pf - formation We pressure <br /> fo: the case of hydraulic pressure behind <br /> The equation cam be simplified <br /> an acid mine drainage bulkhead is a.tunnel. First, the tensile strength can <br /> be assumed to be zero because the rock adjacent to a tunnel is jointed and <br /> er <br /> generally damaged by blasting.. The packed section of a drillbole, on the <br /> other hand, can be entirely within one joint block and is <br /> not ubject to <br /> acaitt to a <br /> blasting. Second.' the pare pressure present near surfa and adjacent <br /> - <br /> -- tunnel must:be low and can be assumed to be Finally;-in the absence of <br /> �•timate the stresses in the <br /> in situ stress measurements it is necessary <br /> -13- ' <br />