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154 by the American Association of Highway and Transportation Officials (AASHTO) in 1986 prescribed a minimum specimen diameter 6 times the largest particle size. Taylor (1971) investigated the effect of specimen height to diameter ratios in repeated load triaxial testing results. He concluded that if the height of the specimen is about twice its diameter, the significance of size effect on the measurements would be negligible. Similar conclusions were drawn by Dehlen (1969) based on a theoretical study on the same issue. The publications from TRB (1975) and AASHTO (1986) also specified a minimum specimen height of twice the diameter. According to the draft of European Standard prEN 13286-7 (2002), the tested specimen must have a diameter larger than 5 times the maximum particle size of the material and a height twice the diameter (± 2 %). Most repeated load triaxial testing facilities currently available have specimen diameters of 300 mm, 150 mm, or even less (Lekarp 1999). 8.5 General guidelines on instrumentation Monitoring the response of the specimen during triaxial testing requires proper instrumentation for measuring both the applied stresses and the induced strains. The tests can be performed more efficiently if the measuring devices are kept outside the pressure vessel. In this way, the deformation transducers would be constantly accessible for possible adjustments. Furthermore, water could be used as the confining medium, being an inexpensive alternative to special hydraulic oils such as silicone oil. However, keeping the devices outside the pressure cell could lead to erroneous measurements due to the impact of factors such as the stiffness of the loading system, the friction between the specimen and the loading platens, and the friction between the loading piston and the cell bush (Lekarp 1999). For reasons such as these, it is generally considered important to place the measuring devices inside the triaxial cell and in direct contact with the specimen. In such cases, however, the devices are directly exposed to the confining medium, and it is essential to make sure that such exposure does not affect the electrical output signals. Silicone oil is normally recommended as the confining medium since it is chemically inert and is an excellent electrical insulator. It is also important for the load cell to be constructed so that its output signal is not influenced by the applied confining pressure (Lekarp 1999). When measuring the vertical deformation of the specimen, the influence of the deformation due to bedding of the loading platens and the friction between the specimen and these platens could be eliminated if the displacement is measured between two fixed points on the specimen itself. In regard to the monitoring of the lateral deformation, the technique employed should provide a reliable measurement of the average displacement along the circumference of the specimen (Lekarp 1999). 8.6 University of Nottingham’s repeated load triaxial apparatus 8.6.1 Introduction A repeated load triaxial apparatus has been developed at the University of Nottingham with some modifications made over the years. The apparatus in question has been used
155 for projects on the behaviour of unbound granular materials by many researchers, among whom Lekarp in 1997 and Werkmeister in 2003. The principal components of the repeated load triaxial apparatus analysed in this section are illustrated in Figure 8.6.1:1. Figure 8.6.1:1 Repeated load triaxial apparatus (Boyce 1976). The loading system is a hydraulic servo-controlled system, in which both axial load and confining pressure are applied to the specimen in a triaxial cell by hydraulic actuators. The axial load is applied by a 50.8 mm diameter hydraulic actuator, capable of applying a deviator stress of up to 1,200 kPa on samples of 150 mm diameter and 300 mm height, at frequencies up to 16 Hz. The axial load is monitored continuously by a load cell. The electronic control system compares the output from the load cell with a load applied to the servo-valve on the actuator in order to adjust the applied load to that required.
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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
Page 106 and 107: 104 Chan (1990) noticed, in his stu
Page 108 and 109: 106 Youd (1972) studied the behavio
Page 110 and 111: 108 Figure 6.5:2 Comparison of plas
Page 112 and 113: 110 ample fine-grained fractions th
Page 114 and 115: 112 of a dolomitic limestone with a
Page 116 and 117: 114 Fuller curve (Equation 4.6.2:3)
Page 118 and 119: 116 Figure 6.6:7 Elastic and plasti
Page 120 and 121: 118 Figure 6.7:1 Dependence of the
Page 122 and 123: 120 0,7 0,6 Elastic limit Failure s
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
Page 154 and 155: 152 aim to simulate as closely as p
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
Page 166 and 167: 164 through each platen is provided
Page 168 and 169: 166 measured for the 600 mm central
Page 170 and 171: 168 displayed on the monitor in gra
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
Page 180 and 181: 178 under the same isotropic stress
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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