非饱和土受压变形的简化计算研究

Simplified computation of deformation for unsaturated soil under compression loads

非饱和土的固结问题是岩土工程研究中非常复杂的热门课题。本文拟将非饱和土受压后的固结过程简单地分为压密和固结两个阶段。在压密过程中,与饱和土固结不同是,由于非饱和土的孔隙水、气来不及排出,与骨架共同承担荷载,产生了超孔隙气压和超孔隙水压,这个阶段土体变形主要是压缩孔隙气产生的压缩变形;固结阶段,土体在恒定荷载作用下,超孔隙气压和超孔隙水压逐渐消散而固结。对于饱和度较高的地基土,将水、气可看作混合流体,并考虑残留混合流体的压缩性,建立平衡微分方程和混合流体的连续方程,求出有效应力和混合流体压力;土体中水压力可通过水连续方程求出,继而求出气压力、吸力等。最后算例表明:加载过程中,有效应力、混合流体压力、水压力不断增大,吸力不断减小;竣工后,混合流体压力、水压力还在增长;由加载产生变形以荷载压密变形为主,之后变形增量逐渐减小。这与路堤填筑过程中的监测结果相一致,说明本文的简化方法是合理的。因此本文的非饱和土固结研究对于促进了非饱和土固结变形计算走向实用化,具有重要的工程意义。

The consolidation of unsaturated soil was simplified into two stages. During the first stage, the water and air in the pores could not be drained immediately and could support the loads together with soil skeleton, and the pore pressure of water and air would rise. The soil was compressed immediately and the suction was reduced because of the compression of the air in the pore. During the second stage, the excess pore pressure was dissipated under the constant loads. Water and air in the pores could be regarded as a mixed fluid with high degree of saturation. Balanced differential equations and continuous equations of pore fluid were established regarding the compressibility of the mixed fluid in the pores. Then the effective stress and mixed fluid pressure could be computed. It was shown by a numerical example that the effective stress, pore pressure of mixed fluid and pore-water pressure increased and the suction decreased during the process of loading, and the pore pressure of mixed fluid and the pore-water pressure continued to increase after the completion of loading, and the majority of deformation occurred during the compression stage. All of these were similar to the monitored results in the process of embankment construction. Therefore, the approach was reasonable and very important to promote practical computation of consolidation deformation.