Experimental Study On Deformation Characteristics Of Rockfill With Local Measurement Method

Rockfill is an important component of geotechnical structures such as earth rock dams.A large number of earth rock dams show that the actual stress state of most areas of dam is far less than the peak stress state of rockfill.The body of dam is generally in a small stress state during the dam filling and running.So it is very important to measure the deformation characteristics of rockfill in the small strain stage when evaluating the deformation of the dam.But because of the existence of end errors,the traditional measurement method of large triaxial apparatus cannot accurately measure the deformation characteristics of rockfill in the small strain stage.On the other hand,most of the results on the dynamic deformation characteristics of rockfill were obtained by the traditional measurement method of large triaxial apparatus.The information on the dynamic deformation characteristics of rockfill based on local measurement technology was still small.In view of the above problems,local axial displacement transducer and radial displacement transducer were used in the large triaxial apparatus,measuring the local axial strain and radial strain directly and eliminating the effects of the end errors.The following results were carried out:(1)Aiming at the shortages of the traditional measurement method of large triaxial apparatus in the axial deformation measurement,the measuring principle,structure,production materials and production method of the local axial displacement transducer were introduced in detail by using the latest waterproof strain gauge.(2)By using the local measurement technology,large triaxial tests under monotonic loading conditions were carried out to study the deformation modulus,volumetric strain and poisson’s ratio in the small strain stage.The results show that the secant modulus and tangent modulus measured by the local measurement method are 1.5 to 2.0 times of the result measured by the traditional measurement method when the axial strain is in the range of 0.001% and 0.01%.The traditional measurement method obviously overestimates the volumetric strain and underestimate the radial strain.The poisson’s ratio measured by the local measurement method is about 2.0 times of the result measured by traditional measurement method in the small strain stage.The poisson’s ratio measured by the local measurement method under different confining pressures changed from 0.1 to 0.2.When the axial strain is equal,the poisson’s ratio decreased with confining pressure increasing.(3)By using the local measurement technology,the dilatancy regularity of rockfill was studied.The results show that the Nova dilatancy equation can well fit the relationship between the dilatancy ratio and the stress ratio measured by the local deformation measurement method.In the low stress ratio stage,the dilatancy ratio measured by the traditional measurement method is nonlinear with the stress ratio.The Nova dilatancy equation cannot fit the data measured by the traditional measurement method in the low stress ratio stage,which may be due to the problem of the end errors.The phase-transformation stress ratio increased with the confining pressure increasing.(4)By using the local measurement technology,large triaxial tests under cyclic loading were carried out to study the dynamic shear modulus and damping ratio.The results show that the maximum dynamic shear modulus increased with the the confining pressure and the initial consolidation ratio increasing,and decreased with the void ratio increasing.The greater the confining pressure and the initial consolidation ratio,the slower the normalized shear modulus attenuated.The damping ratio increased with the increase of the shear strain,and the influence of the confining pressure on the damping ratio was significant,the damping ratio decreased with the confining pressure increasing.