Sector 1 of the vault (6.1 feet [1.87 m] long) is interested by a flow that can be calculated by means of the equation. qsector 1 = Q · Lsector 1 / Ltotal = 11.25 m³/h/m · 1.87 m / 11.88 m = 1.77 m³/h/m Sector 2 (immediately below the first) should guarantee a draining capacity equal to the one required by sector 1 (as its length is the same), plus the water coming from sector 1. qsector 2 = qsector 1 + Q · Lsector 2 / Ltotal = 1.77 m³/h/m + 11.25 m³/h/m · 1.87 m / 11.88 m = 3.54 m³/h/m The normal pressure acting on each sector of the tunnel has been calculated projecting the vertical and horizontal pressure (assumed constant for the entire height of the tunnel) along the direction orthogonal to the sector surface. With θ as the angle between the radius of the considered segment and the horizontal direction, the normal stress can be calculated as: σn = σv sen θ + σh cos θ The results obtained for the critical part (LEFT/RIGHT) are summarized in Table 3. FIGURE 5 Driskos Tunnel geometry with the sectors used in the calculation TABLE 3 Flow calculations for LEFT/RIGHT conditions (maximum hydraulic flow rate: 11.25 [m³/h/m]) 3 Sector 1 2 3 4 5 6 ∑ Larc [m] 1.87 1.87 1.87 1.87 1.87 2.53 11.88 GeosyntheticsMagazine.com 31 Lsector [m] 1.86 1.86 1.86 1.86 1.86 2.53 θ [º] 90 72 54 36 18 i [rad] 0.16 0.45 0.71 0.89 0.99 1.00 [m3/h/m] 1.89 3.78 5.67 7.55 9.44 12.00 q [m3/sec/m] 4.92E-04 9.84E-04 1.48E-03 1.97E-03 2.46E-03 3.13E-03 ireΓ [rad] 0.10 0.50 1.00 1.00 1.00 1.00 qreΓ [m3/sec/m] 4.92E-04 9.84E-04 1.48E-03 1.97E-03 2.46E-03 3.13E-03 σn [kPa] 159.89 148.30 178.11 190.47 184.20 103.98 Rock classification 4 σn [kPa] 331.20 348.98 380.41 402.89 385.94 229.58 Figure 6 on page 32 shows flow-rate diagrams for geosynthetics products used, depending on the rock condition. In the flow diagrams, the critical conditions are identified through colored stars: red star = sector 1; blue star = sector 2; green star = sector 4; violet star = sector 6. The red star should be compared with the curve obtained at gradient 0.10, the blue star with the curve at gradient 0.50, and the green and violet stars with the curve at gradient 1.00. The same flow rate applies to different values of the 5 σn [kPa] 502.52 506.34 651.31 665.14 613.88 439.96http://www.GeosyntheticsMagazine.com