Crushed latite basalt is commonly used as railway ballast in Australia [5, 12]. It is well established that breakage of grains influences the strength and deformation behaviour of soils [5, 7, 8, 9, 11, 12]. The intensity of breakage is a function of granulometry, stress level and deformation process [6, 9]. Cyclic loading significantly intensifies particle breakage . Marsal’s breakage index  and ballast breakage index  are the widely used parameters of ballast breakage.
The breakage of particles reduces angularity and thus reduces friction as well as the critical state friction angle of ballast [2, 5, 15].The critical state fiction angle of sands is independent of breakage of grains [1, 3, 10]. The peak friction angle is also reduced by the growth of confining pressure without particle breakage. The separation of stress level influence and particle breakage influence on the behaviour of crushed latite basalt is very difficult and has not been proposed in literature until now. The large-scale triaxial testing of latite basalt at large axial strains exceeding 20–25% shows the continual breakage of particles. There were little or no volume changes at almost constant stress at large strains, so the reduction of critical state parameters is natural in the modelling of latite basalt behaviour.
During monotonic shearing, the total plastic work’s components are purely shearing, some part of volume changes (not natural dilatancy) during shear and particle breakage. The natural dilatancy, characteristic for each soil, caused by shear has no influence on energy dissipation . Salim and Indraratna  stated that the increment in energy consumption because of particle breakage per volume unit is proportional to the breakage index increment.
Szypcio  developed
and the value of the mobilised angle of shear resistance
The plastic part of volume
and for convenitional triaxial tests
The crushed latite basalt was tested by Salim and Indraratna  and Indraratna et al.  at drained conditions using a large-scale cylindrical triaxial apparatus. The initial void ratio was e = 0.76. The relationships
In Figure 1, the relationships
The points representing maximum curvature of
In the author’s opinion, if there is no particle breakage, the
This influence is significant for crushed latite basalt even at low confining pressure and small values of plastic dilatancy. This is probably due to a low number of contact points between particles. In these contact points, there appeared very high stress and intense crushing.
At the initial phase of shearing, the mean normal stress increments are high and play a dominant role in particle breakage. At the advanced phase of shearing, the mean normal stress increments are relatively small and shear deformation plays a dominant role in particle breakage. The
It may be accepted that
The values of
Parameters Indraratna et al. (2015) Salim and Indraratna (2004) Confining pressure σc (kPa) 30 60 180 360 50 100 200 300 2.50 –3.60 –3.30 –7.70 5.00 –3.00 –4.00 –7.00 –25.0 18.00 10.00 13.00 –19.00 15.00 13.00 12.00 –0.35 0.55 1.10 2.00 –0.20 0.65 0.90 0.95 1.00 2.20 3.80 2.40 1.00 2.70 4.50 3.20
The values of
At the initial stage of deformation, parameters
On the contrary, if
The value of
Stress–strain behaviour of crushed latite basalt may be successfully analysed by using
The stress–dilatancy relationship is bilinear. At the initial stage of shearing, the breakage of particles is predominantly caused by the mean normal stress increments. At the advanced stage, the breakage of particles is mainly caused by shear deformation.
Particle breakage significantly influences the stress–dilatancy relationship for crushed latite basalt, even at a low stress level.
The results of this article show that
The values of α and β for triaxial compression of crushed latite basalt.
|Parameters||Indraratna et al. (2015)||Salim and Indraratna (2004)|
|Confining pressure σc (kPa)|
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