OCR Text |
Show intersects the f - axis at f, , the criteria of primary stability is simply ( 10) " T) , is found from Coi WJ 3t f l s^ do where M, the " compressibility," is defined as M-_ wt- 2. 2VH - Z. 0 ^ M ^ > £ ( 12) \ Let us first consider homogeneous slabs of equal thickness and examine the variation of stability with slope angle. In Fig. 4, '/\ is shown as a function of Y for different values of the parameter 00 , and for two extreme values of It can be observed that for slabs of equal thickness, steeper slopes are more criti cal. However, let us next consider the case of slab thickness varying with the slope angle. This situation is observed when snow falls with little wind. Then, ^ must be replaced by °^ t US/^ , where ° S^ is the slab thickness on level terrain. As shown in Fig. 5, the shape of the curves change. ' 7~) is maximum between 35 and 50 for ni = oo ; and is maximum between 45 and 65 for Vn = £ . This indicates that if ^ increases progressively up to " T^ ( a continuous fall of snow), slopes of about 45 rupture before the steeper slopes. If only slopes of practical interest are considered, say below 50 , primary stability is assured for all slopes if the load, <^ , is less than 80% of T a ( 60% with constant snow height). Since stability varies as ft changes, it is possible to define a limiting slope which is " absolutely stable" independent of an increase in 5 . In fact, it can be seen in Fig. 4 and Fig. 5 that if rVt is small enough, TJ can be less |