1、Section 15 STEEL TUNNEL LINER PLATES 15.1 GENERAL AND NOTATIONS 15.1.1 General 15.1.1.1 These criteria cover the design of cold- formed panel steel tunnel liner plates. The minimum thickness shall be as determined by design in accordance with Articles 15.2,3,4,5, and 6 and the construction shall con
2、form to Section 26-Division II. The supporting Ca- pacity of a nonrigid tunnel lining such as a steel liner plate results from its ability to deflect under load, so that side restraint developed by the lateral resistance of the soil constrains further deflection. Deflection thus tends to equalize ra
3、dial pressures and to load the tunnel liner as a compression ring. 15.1.1.2 The load to be carried by the tunnel liner is a function of the type of soil. In a granular soil, with little or no cohesion, the load is a function of the angle of in- ternal friction of the soil and the diameter of the tun
4、nel being constructed. In cohesive soils such as clays and silty clays the load to be carried by the tunnel liner is depen- dent on the shearing strength of the soil above the roof of the tunnel. 15.1.1.3 A subsurface exploration program and ap- propriate soil tests should be performed at each insta
5、lla- tion before undertaking a design. 15.1.1.4 Nothing included in this section shall be in- terpreted as prohibiting the use of new developments where usefulness can be substantiated. 15.1.2 Notations D, = critical pipe diameter (Article 15.3.4) E = modulus of elasticity (Article 15.3.3) FS = fact
6、or of safety for buckling (Article 15.3.4) f, = buckling stress (Article 15.3.4) f, = minimum specified tensile strength (Article H = height of soil over the top of the tunnel (Article I = moment of inertia (Article 15.3.3) k = parameter dependent on the value of the friction P = external load on tu
7、nnel liner (Article 15.2.1) Pd = vertical load at the level of the top of the tunnel liner due to dead load (Article 15.2.1) Pl = vertical load at the level of the top of the tunnel liner due to live load (Article 15.2.1) r = radius of gyration (Article 15.3.4) T = thrust per unit length (Article 15
8、.3.4) W = total (moist) unit weight of soil (Article 1 5.3.4) 15.2.4) angle (Article 15.3.4) 15.2.4) = friction angle of soil (Article 15.3.4.1) 15.2 LOADS 15.2.1 External load on a circular tunnel liner made up of tunnel liner plates may be predicted by various meth- ods including actual tests. In
9、cases where more precise methods of analysis are not employed, the external load P can be predicted by the following: (a) If the grouting pressure is greater than the com- puted external load, the external load P on the tunnel liner shall be the grouting pressure. (b) In general the extemal load can
10、 be computed by the formula: A = cross-sectional area of liner plates (Article P = Pl + Pd (15-1) 1 5.3.4) Cd = coefficient for tunnel liner, used in Marstons where: formula (Article 15.2.4) P = the external load on the tunnel liner; D = horizontal diameter or span of the tunnel (Arti- cle 15.2.4) D
11、 = pipe diameter (Article 15.3.3) PI = the vertical load at the level of the top of the tunnel liner due to live loads; 403 404 HIGHWAY BRIDGES 15.2.1 Pd = the vertical load at the level of the top of the tunnel liner due to dead load. 15.2.2 For an H 20 load, values of Pl are approximately the foll
12、owing: H(ft) 4 5 6 7 8 910 Pl (lbpersqft) 375 260 190 140 110 90 75 15.2.3 Values of Pd may be calculated using Marstons formula for load or any other suitable method. 15.2.4 In the absence of adequate borings and soil tests, the full overburden height should be the basis for Pd in the tunnel liner
13、plate design. The following is one form of Marstons formula: Pd = CdWD (15-2) where: Cd = coefficient for tunnel liner, Figure 15.2.3A; W = total (moist) unit weight of soil; D = horizontal diameter or span of the tunnel; H = height of soil over the top of the tunnel. 15.3 DESIGN 15.3.1 Criteria The
14、 following criteria must be considered in the design of liner plates: (a) Joint strength. (b) Minimum stiffness for installation. (c) Critical buckling of liner plate wall. (d) Deflection or flattening of tunnel section. 15.3.2 Joint Strength 15.3.2.1 The seam strength of liner plates must be suffic
15、ient to withstand the thrust developed from the total load supported by the liner plate. This thrust, T, in pounds per linear foot is: T = PD/2 (15-3) where P = load as defined in Article 15.2, and D = diameter or span in feet. O 1 2 3 Values of coefficient Cd FIGURE 15.2.3A Diagram for Coefficient
16、Cd for Tunnels in Soil (+ = Friction Angle) 15.3.2.2 DIVISION 1-DESIGN 405 15.3.2.2 The ultimate design longitudinal seam strengths are: TABLE 15.3.2.2 Ultimate Seamstrength of Liner Plates Plate Thickness Ultimate Strength, (in.) (kips/ft) 0.075 20.0 0.105 30.0 26.0 0.135 47.0 43.0 o. 164 55.0 50.0
17、 O. 179 62.0 54.0 0.209 87.0 67.0 0.239 92.0 81.0 0.313 115.0 0.375 119.0 2 Flange 4 Flange 15.3.2.3 The thrust, T, multiplied by the safety fac- tor, should not exceed the ultimate seam strength. 15.3.3 Minimum Stiffness for Installation 15.3.3.1 The liner plate ring shall have enough rigid- ity to
18、 resist the unbalanced loads of normal construction: grouting pressure, local slough-ins, and miscellaneous concentrated loads. The minimum stiffness required for these loads can be expressed for convenience by the formula below. It must be recognized, however, that the limiting values given here ar
19、e only recommended minima. Actual job conditions may require higher values (greater effective stiffness). Final de- termination on this factor should be based on intimate knowledge of the project and practical experience. 15.3.3.2 The minimum stiffness for installation is de- termined by the formula
20、: Minimum stiffness = EID2 (15-4) where: D = diameter in inches; E = modulus of elasticity, psi (29 X lo6); I = moment of inertia, inches.to the fourth power per For 2-Flange (Em2) = 50 minimum; For 4-Flange (Em2) = 111 minimum; inch; 15.3.4 Critical Buckling of Liner Plate Wall 15.3.4.1 Wall buckli
21、ng stresses are determined from the following formulae: For diameters less than D, the ring compression stress at which buckling becomes critical is: For diameters greater than D,: 12E in psi f, = (kD/r)2 (15-6) where: D, = (r/k)dm = critical pipe (15-7) diameters in inches; f, = minimum specified t
22、ensile strength in pounds per square inch; fc = buckling stress in pounds per square inch, not to exceed minimum specified yield strength; D = pipe diameter in inches; r = radius of gyration of section in inches per foot; E = modulus of elasticity in pounds per square k will vary from 0.22 for soils
23、 with 4 15 to 0.44 for inch. soils 4 15. 15.3.4.2 Design for buckling is accomplished by lim- iting the ring compression thrust T to the buckling stress multiplied by the effective cross-sectional area of the liner plate divided by the factor of safety. T=- fCA FS (15-8) where: T = thrust per linear
24、 foot from Article 15.3.2; A = effective cross-sectional area of liner plate in square inches per foot; FS = factor of safety for buckling. 15.3.5 Deflection or Flattening 15.3.5.1 Deflection of a tunnel depends significantly on the amount of over-excavation of the bore and is af- fected by delay in
25、 backpacking or inadequate backpack- ing. The magnitude of deflection is not primarily a func- tion of soil modulus or the liner plate properties, so it cannot be computed with usual deflection formulae. 15.3.5.2 Where the tunnel clearances are important, the designer should oversize the structure t
26、o provide for a normal deflection. Good construction methods should result in deflections of not more than 3% of the normal diameter. 406 HIGHWAY BRIDGES 15.4 15.4 CHEMICAL AND MECHANICAL REQUIREMENTS 15.4.1 Chemical Composition TABLE 15.5B Section Properties for Two-Flange Liner Plate Effective Mom
27、ent Thickness Area of Inertia (in.) (in.%.) (i/in.) Base metal shall conform to ASTM A 569. 15.4.2 Minimum Mechanical Properties of Flat Plate Before Cold Forming Tensile strength = 42,000 psi Yield strength = 28,000 psi Elongation, 2 inches = 30 percent 15.4.3 Dimensions and Tolerances Nominal plat
28、e dimensions shall provide the section properties shown in Article 15.5. Thickness tolerances shall conform to Paragraph 14 of AASHTO M 167. 15.5 SECTION PROPERTIES The section properties per inch of plate width, based on the average of one ring of linear plates, shall conform to the following: TABL
29、E 15.5A Section Properties for Four-Flange Liner Plate Effective Moment Thickness Area Area of Inertia Gage (in.) (in.%.) (in.%) (in.4/in.) 12 11 10 8 7 5 3 1/4 5/16 3/8 o. 105 O. 133 O. 067 0.042 0.1196 0.152 0.076 0.049 O. 135 O. 170 0.085 0.055 o. 164 0.209 o. 105 0.070 O. 179 0.227 0.114 0.075 0
30、.209 0.264 0.132 0.087 0.239 0.300 o. 150 o. 120 0.250 0.309 0.155 0.101 0.3125 0.386 O. 193 O. 123 0.375 0.460 0.230 O. 143 0.075 0.096 0.034 0.105 0.135 0.049 0.135 O. 174 0.064 o. 164 0.213 0.079 O. 179 0.233 0.087 0.209 0.272 O. 103 0.239 0.312 o. 118 15.6 COATINGS Steel tunnel liner plates shal
31、l be of heavier gage or thickness or protected by coatings or other means when required for resistance to abrasion or corrosion. 15.7 BOLTS 15.7.1 Bolts and nuts used with lapped seams shall be not less than Y8 inch in diameter. The bolts shall conform to the specifications of ASTM A 449 for plate t
32、hickness equal to or greater than 0.209 inches and A 307 for plate thickness less than 0.209 inches. The nut shall conform to ASTM A 307, Grade A. 15.7.2 ter for all plate thicknesses. Circumferential seam bolts shall be A 307 or bet- 15.7.3 Bolts and nuts used with four flanged plates shall be not
33、less than YZ inch in diameter for plate thicknesses to and including 0.179 inches and not less than Y8 inch in diameter for plates of greater thickness. The bolts and nuts shall be quick acting coarse thread and shall conform to ASTM A 307, Grade A. 15.8 SAFETY FACTORS Longitudinal test seam strength = 3 Pipe wall buckling =2
