孔隙率对堆石料强度与变形的影响规律

针对拟建某300m级高土石心墙堆石坝所用堆石料,开展了不同孔隙率的大型静力三轴试验,分析了孔隙率对堆石料的强度和变形的影响。试验结果表明:随着孔隙率的增加,堆石料的峰值强度会减小,体积变形逐渐增大,剪切至峰值点时的剪切位移增大,剪切至出现最大体积变形的剪切位移也会增加,随着围压的升高,颗粒出现一定量的破碎;在邓肯–张和南水模型中表现为参数K,dn值的减小和n,dc,dR值的增大等趋势。分析其原因主要是:随着孔隙率的增加,颗粒内部空隙增多,颗粒间间距增大,颗粒间的接触点减少,在相同围压及剪应力作用下,体积变形增大,最大减缩体应变对应的偏应力也会增加;孔隙率的增加,颗粒间的间距增大,颗粒间的咬合作用减弱,导致堆石料的初始切线模量减小,颗粒抵抗外力的作用减弱,颗粒间内摩擦角与抗剪强度的减小。此外,5P(27)的含量对堆石料的强度和变形作用较为明显,孔隙率相同的情况下,峰值强度、最大体积变量、剪切至峰值强度点对应的剪切位移以及最大体积应变对应的剪切位移均会随5P(27)含量的增加会而增大。孔隙率的变化对堆石料强度和变形影响非常明显,建议堆石坝施工现场碾压时严格控制压实度以满足设计要求,确保大坝安全。

Effects of porosity on strength and deformation of rockfill materials

In view of the rockfill materials utilized in a 300 m - grade high earth-rock core rockfill dam to be constructed, large static triaxial tests under different porosities are performed to analyze the influences of porosity on strength and deformation of rockfill materials. The test results show that with the increase of porosity, the peak strength of rockfill materials decreases and the volume deformation gradually increases. Also, the shear displacement at the peak point increases, and the shear displacement corresponding to the maximum volumetric deformation also increases. With the increase of the loading confining pressure, the particles will be broken to some extent. Thus, these conditions are reflected in the parameters of the Duncan-Chang and the NHRI Constitutive models as follows: the parameters k and n_d decrease, and n, c_d and R_d increase when the porosity increases. The main reason is that with the increase of porosity, the internal porosity of the particles increases, the interparticle spacing increases, and the contact points between the particles decrease. Under the same confining pressure and shear stress, the volume deformation increases and thus the deviatoric stress corresponding to the maximum reduced volume strain increases. Along with the increasing value of porosity, the spacing between particles increases, the interlocking of particles is weakened, the initial tangent modulus of the rockfill is reduced and the ability of particles to resist external force is weakened, which shows that the internal friction angle between particles and the shear strength decrease. In addition, the content of P_<5 has evident effect on the strength and deformation of rockfill materials. In the case of the same porosity, the peak strength, the maximum volume variable, the shear displacement corresponding to the peak shear strength point, and the shear displacement corresponding to the maximum volume strain increase with the increase of percentage of P_<5 contained. It is obvious that the change of porosity has an influence on the strength and deformation of rockfill materials. It is proposed that the degree of compaction should be strictly controlled during the process of on-site rolling compaction to meet the design requirements and to ensure the safety of the dam.