Study On State Dependent Constitutive Model Incorporating Particle Breakage For Coarse Granular Material

Since no engineering example of300m level concrete faced rockfill dam built in theworld, therefore constitutive model reasonable or not is the key problem of accuratepredection on dam deformation and stress characteristics. Good constitutive model willpredict more accurate deformation, guiding the design and construction of dams andsupply the technical support for300m level concrete faced rockfill dam and save hugeamount dam construction investments. Now, the softening or hardening judging methodand the particle breakage problem under extra high pressure becomes the two frontierscientific research topics.The building materials of Shuibuya dam—the highest concrete face rockfill dam inthe world, is chosen as test material. Supported by the natural science foundation—theResearch on asymptotic behavior and particle breakage constitutive model of coarsematerial of extra high300m level concrete faced rockfill dam, large tri-axial tests withmaximum axial strain24%was carried out during2years and50set high quality largetri-axial data was obtained. Due to the limited space,16of55data with sprayed clotheswere used in this paper. Then the analysis is made and the formula in the TechnicalSpecification for Geotechnical Engineering Test of Hydropower is rethinking and modified.A new method, failure surface method, was proposed for maximum shear stress test dataprocessing. The critical state theory is adopted and the state dependent parameters idea isabsorbed. Moreover, a new particle breakage influence factor was submitted to estimateparticle breakage behaviour. Finally, based on state dependent constitutive model of sand(the particle breakage influence is neglected), a state dependent constitutive modelincorporated particle breakage of rockfill material is deduced and submitted. The mainwork and results in this article are shown as follows:1) Indoor large-scale triaxial tests with12main rockfill specimens and4cushion layermaterial of Shuibuya dam have been carried out, and the axial strain24%test data wereobtained.2or3layer latex films with sprayed clothes inside method was tried and thelatex films not tight bonded and brought about water leakage problem was solved usefully.Therefore, high confining pressure tests were carried out successfully, especially the3.5MPa confining pressure test was done successfully and the axial strain attained theseldom seen30%, and the critical point was accurately found out.2) It is first found out that drained tri-axial tests specimen under shearing can be treated as two truncated cones bonded together. The axial stress is equal inside thespecimen assumption is adopted and the force balance equation is set up, then themaximum shear stress formula is deduced. It is the same as that in regulation, whichbrought about the new thinking on the maximum shear formula, and opened up the road tothe following failure surface new method.3) It is first found out that the critical state point location on high confining pressuretri-axial specimen determined by maximum shear stress is not the same with that byvolumetric strain, which is in contradiction with the definition in Advanced Soil Mechanicsthat the critical state point is unique. Most important of all, it is first found out that the statedependent parameter larger than zero for specimen subjected to confining pressure higherthan1.8MPa. Therefore, the rockfill is located to loose side and the stress-strain curveshould have be hardening. However, the curve shape was drawn as softening according tothe formula in regulation. The above two problems proved that for high density rockfillmaterial under high confining pressure, the regulation formula brought about more errorson calculated maximum shear stress. The paper holds that the fundamental cause lies onthe unreasonable assumption in regulation that the axial stress at different height ofspecimen is all the same.4) It is first found out that the inclined failure surface existed when the specimen isunloaded. After analysis the crack distribution regulation of sprayed clothes, it is found outthat the failure surface general exists. The maximum shear stress is equal to the maximumprincipal stress subtracts the minor principal stress. The critical state point on shear stress-axial strain curve determined by the new formula is unique and it conforms to thedefinition of critical state in Adavance Soil Mechnics. Moreover, the test curves drawn bynew failure surface formula were in good agreement with the softening or hardeningcharacteristic which is distinguished by state parameter, the new formula overcomes theshortcomings in regulation formula.5) Based on the high quality tri-axial test particle breakage gradation curves, it is firstadd the newly submitted particle breakage influence factor which can describe thehardening law of rockfill by considering both the macro particle breaking and the confingpressure influence. The modified Rowe dilation equation for sand is explored for rockfillmaterial. Finally, a state dependent constitutive model incorporating particle breakage forcoarse granular soil under high confining pressure is proposed. The prediction accuracy fortest data curves is well. After the comparison with the only found2articles which related to state dependent constitutive model incorporated particle breakage of rockfill material, iswas proved that the new formula is more accurate than the existing old ones.