Deformation behaviour of railway embankment ... - Liikennevirasto

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168 displayed on the monitor in graphical form at any time during the test. The results can also be stored in data files for later analysis. Equipment factors There is a possibility that some characteristics of the equipment influence the triaxial testing results. These influences should be appreciated, and the data corrected if necessary. These factors and their possible impacts are discussed below. − Stiffness of the loading frame → The loading frame undergoes a certain amount of deformation due to the loads applied during testing. If the deformations in the specimen are measured relative to the loading frame, then the results will need to be corrected accordingly. As described previously in this section, the new testing equipment provides direct on-sample instrumentation. The data, therefore, are not affected by the deformation of the loading frame. In addition, the stiffness of the loading frame is important for the amount of energy stored in the frame during loading. If the loading frame is not sufficiently stiff, the energy stored will be released and transferred uncontrollably to the specimen at the start of unloading. This has been taken into consideration in the design of the loading frame provided. The loading frame is sufficiently stiff for the range of loadings that can be applied. − Friction between the loading piston and the cell bushing → As the loading piston slides through the bushing in the cell top platen, some energy is lost due to friction. When the load cell is placed outside the cell, the axial load measurements will differ from the actual load applied to the specimen. Even though the amount of friction could be reduced greatly by using a linear ball bushing, it will not be eliminated entirely. In the equipment the load cell is placed on the lower portion of the piston inside the triaxial chamber. The effect of friction is, thus, eliminated altogether, and the readings show the actual axial loads applied. − Friction between the loading platens and the specimen → Large and unquantifiable deformations occur at the interface between the specimen and the loading platens. Consequently, if the axial load displacement is measured over the entire height of the specimen, the strain data will, in fact, be erroneous. To overcome this problem, strain determination in the new equipment is confined to the 600 mm central portion of the specimen. − Fluid leakage into the specimen → The ingress of the confining silicone oil into the specimen will almost certainly disturb the behaviour of the material. The extent of the impact will depend on the amount of the leaked oil, but is extremely difficult, if not impossible, to quantify. Because of the uncertainties arising from the ingress of oil into the specimen, great care must be taken to avoid this problem. Replacing a specimen spoilt by a leaking membrane is very costly in terms of both time and effort. In the testing equipment, the specimen is covered by two neoprene membranes, sealed at each end to the loading platen by a clamp. Before the outer membrane is placed over the specimen, it is checked for any flaws or leaks. A leak test is performed by sealing each end of the membrane over a purpose-made PVC platen. One of the platens is provided with a sealed outlet, which is connected to a compressed air supply for filling the membrane. As the membrane inflates, it is
169 examined for leaks through pinholes. At the same time, the surface of the membrane is inspected visually for any flaws, such as trapped air bubbles that could burst during the test. The membrane must be discarded if there are any doubts regarding its sealing capabilities. − Change in cross-sectional area of the specimen → The actual deviatoric stress applied to the specimen changes during a triaxial test as the cross section of the specimen changes due to radial plastic strain. The cross-sectional area of the specimen, A, at any moment during triaxial testing can be calculated according to A = A 0 + 2πε R 3, p 2 , [Eq. 8.7.2:1] where A 0 = original cross-sectional area, R = radius of the specimen, ε 3,p = radial permanent strain induced. The amount of plastic strain during a resilient test is practically none, or negligible. This is due to the fact that, prior to resilient testing, the specimen is brought to a stable state by conditioning. However, a significant amount of plastic strain accumulates during conditioning and permanent strain tests. For these cases, the cross-sectional area of the specimen should be corrected accordingly. − Membrane stiffness → The membranes enclosing a triaxial specimen may have a certain restraining effect on the specimen, thereby reducing the strain caused by the deviator stress. For specimens of high strength materials or with large diameters, the effect of the membrane restraint is considered to be insignificant (Head 1994). 8.7.3 Description of the test series performed by Lekarp (1999) Following the construction of the triaxial apparatus, a test program was planned, partly to evaluate the performance of the equipment and partly to characterize the resilient response of several unbound granular materials. The tests were all conducted in drained condition, thus allowing the pore pressure to dissipate as the tests proceeded. Each test was performed by the application of repeated deviatoric and confining stresses, while the induced axial and radial strains were measured. 8.8 Laboratoire des Ponts et Chaussées’ repeated load triaxial apparatus 8.8.1 Introduction Gidel et al. (2004) proposed a new approach for studying permanent deformation in unbound granular materials under cyclic loading. The approach is based on results of laboratory tests performed with the repeated load triaxial apparatus. The repeated load triaxial apparatus was developed in order to investigate the mechanical behaviour of
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A 5/2006 Deformation behaviour of r
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Finnish Rail Administration Publica
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4 Past investigations have shown cl
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6 Brecciaroli, Fabrizio - Kolisoja,
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8 kuvataan jakamalla jännitykset j
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10 TABLE OF CONTENTS ABSTRACT .....
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12 8.9 Trondheim NTNU/SINTEF’s re
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14 combination of resilient strains
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16 Modelling is an important necess
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18 Figure 2.1:2 Two-dimensional sta
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20 σ xx − σ 3 2 det τ yx σ yy
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22 stresses. As it can be seen from
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24 grains. The resistance to partic
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26 The reason was argued to be that
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28 term matric suction implies the
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30 Figure 3.2.1:1 Idealisation of t
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32 ε ε 2 ν = , (Eq. 3.2.2:4) whe
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34 where sij = σ −σ , (Eq. 3.2.
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36 addition, when both the complexi
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38 supplement continuum mechanics m
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40 Figure 4.2:1 A typical variation
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42 Figure 4.2:3 Modulus of resilien
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44 provided that the applied stress
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46 material (Uzan 1985). Dilation i
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48 Figure 4.5:1 Resilient modulus o
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50 The grain size distribution of g
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52 The grain sizes that determine t
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54 4.6.3 Fines content A simple cha
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56 grained than for fine-grained ag
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58 and the shape of the particles a
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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
Page 120 and 121: 118 Figure 6.7:1 Dependence of the
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Page 124 and 125: 122 Figure 6.8.1:1 Influence of fin
Page 126 and 127: 124 explain why the differences in
Page 128 and 129: 126 was then argued that the variat
Page 130 and 131: 128 7 MODELLING OF PERMANENT DEFORM
Page 132 and 133: 130 Figure 7.2:1 Mohr-Coulomb repre
Page 134 and 135: 132 where K p (N) = bulk modulus wi
Page 136 and 137: 134 1993)) have reported that at le
Page 138 and 139: 136 ε 1,p = accumulated permanent
Page 140 and 141: 138 Barksdale (1972) conducted repe
Page 142 and 143: 140 Figure 7.6:2 Relationship betwe
Page 144 and 145: 142 also be employed for pavement d
Page 146 and 147: 144 repeated loads, although adapta
Page 148 and 149: 146 series of specimens (or in a mu
Page 150 and 151: 148 Figure 7.7:5 S-N design models
Page 152 and 153: 150 In conclusion, both Huurman (19
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Page 158 and 159: 156 Confining pressure is applied t
Page 160 and 161: 158 particles. During the test, the
Page 162 and 163: 160 method takes the average value
Page 164 and 165: 162 Figure 8.7.2:2 Schematic illust
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Page 168 and 169: 166 measured for the 600 mm central
Page 172 and 173: 170 unbound granular materials. The
Page 174 and 175: 172 Figure 8.8.2:2 Permanent axial
Page 176 and 177: 174 performance-related (functional
Page 178 and 179: 176 the six supports of the vertica
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Page 182 and 183: 180 9 CONCLUSIONS 9.1 Resilient def
Page 184 and 185: 182 − Permanent deformation resis
Page 186 and 187: 184 Balay J., Gomes Correia A., Jou
Page 188 and 189: 186 Cheung, L.W. (1994). Laboratory
Page 190 and 191: 188 El abd, A., Hornych, P., Breyss
Page 192 and 193: 190 Hoff, I., Nordal, S., and Norda
Page 194 and 195: 192 Kolisoja, P. (1996b) Large Scal
Page 196 and 197: 194 Mitry, F.G. (1964). Determinati
Page 198 and 199: 196 Plaistow, N.C. (1994). Non-Line
Page 200 and 201: 198 Tam, W.A. and Brown, S.F. (1988
Page 202 and 203: 200 Wellner, F. (1996). Influence o
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