Deformation behaviour of railway embankment ... - Liikennevirasto

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12 8.9 Trondheim NTNU/SINTEF’s repeated load triaxial apparatus.............................. 173 8.10 Triaxial tests with measurement of negative pore pressure.................................. 174 9 CONCLUSIONS ....................................................................................................... 180 9.1 Resilient deformation behaviour ............................................................................ 180 9.2 Permanent deformation behaviour ......................................................................... 181 REFERENCES ............................................................................................................. 183 APPENDIX 1 Résumé in Finnish
13 1 INTRODUCTION 1.1 Background Due to the severity of the climatic conditions in Finland, the thickness of the structural layers in all the high-grade railway lines is considerably bigger than in many warmer countries. On the other hand, in order to reduce the expenses, the railway embankments have had to be designed and constructed with relatively narrow widths and steep slopes. As a result, under repeated train loading, gradual, permanent deformation occurs within the railway embankment. Eventually, the deformations lead to the railway embankment being flattened. The optimum width and slope of a railway embankment has great importance, because the widening of the embankment and/or the flattening of its slopes would require considerably high investments. In contrast, the flattening of the railway embankment increases the need for maintenance. As an indirect consequence, the repeated tamping of the track increases the degradation of the ballast. The choices related to the shape and width of the embankment have an especially big importance in those rail sections where the allowed axle loads and train speeds are being increased, because an increase of the trainload always influences the embankment deformation. The values of the static critical loads are generally very high on the railway network compared to the allowed trainloads (Brecciaroli and Kolisoja 2004). However, also the displacements are then so big that, although the real displacements would be only a small fraction of these values, in practice they would not be elastic anymore. This means that stage-by-stage the embankment would collapse. Railway embankments are made of unbound granular materials. These materials are different from most natural soils in their physical characteristics and also in their response to applied cyclic load. One consequence of having a granular nature is that these materials, when untreated, have no inherent strength as a continuum and are unable to withstand any tension. On the other hand, they can support (small) shear stresses indefinitely. Only gravity and applied outside forces create intergranular contact pressures and frictional forces that are able to resist relative movement of particles. Granular interlocking contributes to this type of strength. Placed in a layer and well compacted such materials possess the ability to carry traffic loads and distribute them onto the underlying layers or the sub grade. The deformation resistance of an unbound granular material depends on the applied stresses. The behaviour of unbound granular materials under compressive stresses is highly complex because of the existence of both resilient and permanent strains even at small levels of stress. Unbound granular materials in a railway embankment are subjected to a large number of load cycles during the service life of the embankment. The deformational response of these materials under repeated, traffic-type loading is defined by a resilient deformation response and a permanent deformation response. The resilient strain response is important for the load-carrying ability of the embankment, while the permanent strain response characterizes the long-term deformation behaviour of the embankment. In other words, these layers exhibit a
Page 1: A 5/2006 Deformation behaviour of r
Page 4 and 5: Finnish Rail Administration Publica
Page 6 and 7: 4 Past investigations have shown cl
Page 8 and 9: 6 Brecciaroli, Fabrizio - Kolisoja,
Page 10 and 11: 8 kuvataan jakamalla jännitykset j
Page 12 and 13: 10 TABLE OF CONTENTS ABSTRACT .....
Page 16 and 17: 14 combination of resilient strains
Page 18 and 19: 16 Modelling is an important necess
Page 20 and 21: 18 Figure 2.1:2 Two-dimensional sta
Page 22 and 23: 20 σ xx − σ 3 2 det τ yx σ yy
Page 24 and 25: 22 stresses. As it can be seen from
Page 26 and 27: 24 grains. The resistance to partic
Page 28 and 29: 26 The reason was argued to be that
Page 30 and 31: 28 term matric suction implies the
Page 32 and 33: 30 Figure 3.2.1:1 Idealisation of t
Page 34 and 35: 32 ε ε 2 ν = , (Eq. 3.2.2:4) whe
Page 36 and 37: 34 where sij = σ −σ , (Eq. 3.2.
Page 38 and 39: 36 addition, when both the complexi
Page 40 and 41: 38 supplement continuum mechanics m
Page 42 and 43: 40 Figure 4.2:1 A typical variation
Page 44 and 45: 42 Figure 4.2:3 Modulus of resilien
Page 46 and 47: 44 provided that the applied stress
Page 48 and 49: 46 material (Uzan 1985). Dilation i
Page 50 and 51: 48 Figure 4.5:1 Resilient modulus o
Page 52 and 53: 50 The grain size distribution of g
Page 54 and 55: 52 The grain sizes that determine t
Page 56 and 57: 54 4.6.3 Fines content A simple cha
Page 58 and 59: 56 grained than for fine-grained ag
Page 60 and 61: 58 and the shape of the particles a
Page 62 and 63: 60 Figure 4.7:1 Effect of the wetti
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62 Figure 4.7:3 Modulus of resilien
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64 Figure 4.7:6 Dry -density as a f
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66 Figure 4.7:7 Resilient response
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68 The form index can be measured u
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70 Hovinmoen are gravel materials.
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72 5 MODELLING OF RESILIENT DEFORMA
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74 5.2.2 Resilient modulus as a fun
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76 M r k2 k3 ⎛ θ ⎞ ⎛ q ⎞ =
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78 the model showed good representa
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80 discussed. However it can be exp
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82 et al. (2003) calculated the res
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84 p u = unit pressure (1 kPa), δp
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86 Figure 5.2.5:2 Vertical resilien
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88 2 1 ⎛ ⎞ = A q ε ν p ⎜1
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90 Figure 5.3:2 An example of the c
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92 by incorporating a coefficient o
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94 6 FACTORS AFFECTING PERMANENT DE
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96 cycles. He drew the general conc
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98 accumulated strain, ε p , is co
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100 Figure 6.3:1 Effect of loading
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102 load” is not equal to the fai
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104 Chan (1990) noticed, in his stu
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106 Youd (1972) studied the behavio
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108 Figure 6.5:2 Comparison of plas
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110 ample fine-grained fractions th
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112 of a dolomitic limestone with a
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114 Fuller curve (Equation 4.6.2:3)
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116 Figure 6.6:7 Elastic and plasti
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118 Figure 6.7:1 Dependence of the
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120 0,7 0,6 Elastic limit Failure s
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122 Figure 6.8.1:1 Influence of fin
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124 explain why the differences in
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126 was then argued that the variat
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128 7 MODELLING OF PERMANENT DEFORM
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130 Figure 7.2:1 Mohr-Coulomb repre
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132 where K p (N) = bulk modulus wi
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134 1993)) have reported that at le
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136 ε 1,p = accumulated permanent
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138 Barksdale (1972) conducted repe
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140 Figure 7.6:2 Relationship betwe
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142 also be employed for pavement d
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144 repeated loads, although adapta
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146 series of specimens (or in a mu
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148 Figure 7.7:5 S-N design models
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150 In conclusion, both Huurman (19
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152 aim to simulate as closely as p
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154 by the American Association of
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156 Confining pressure is applied t
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158 particles. During the test, the
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160 method takes the average value
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162 Figure 8.7.2:2 Schematic illust
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164 through each platen is provided
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166 measured for the 600 mm central
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168 displayed on the monitor in gra
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170 unbound granular materials. The
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172 Figure 8.8.2:2 Permanent axial
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174 performance-related (functional
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176 the six supports of the vertica
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178 under the same isotropic stress
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180 9 CONCLUSIONS 9.1 Resilient def
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182 − Permanent deformation resis
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184 Balay J., Gomes Correia A., Jou
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186 Cheung, L.W. (1994). Laboratory
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188 El abd, A., Hornych, P., Breyss
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190 Hoff, I., Nordal, S., and Norda
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192 Kolisoja, P. (1996b) Large Scal
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194 Mitry, F.G. (1964). Determinati
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196 Plaistow, N.C. (1994). Non-Line
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198 Tam, W.A. and Brown, S.F. (1988
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200 Wellner, F. (1996). Influence o
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Liite RHK:n julkaisuun A 5/2006 1 L
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