考虑吸附水的非饱和土耗散本构关系研究
|
摘要
为了探索土水吸附特征对非饱和土力学特性的影响,根据赋存环境把土中水分为储存在毛细管内液面张力吸纳作用占主导的自由水和包裹在土颗粒周围基质静电吸着作用占主导的吸附水。通过把土颗粒基质与吸附水一起共同视为非饱和土骨架相,自由水视为液相、土中气视为气相,获得了考虑吸附水的非饱和土功表达式。根据热力学耗散理论,利用功表达式和局部热力学平衡假定,获得非饱和土在绝热变形过程中的熵流和熵产。基于热力学吸附平衡理论获得土中吸附水的吸附方程,进而提出具有实用性的吸附水土-水特征曲线。利用熵产表达式中的热力学共轭量和耗散空间的Drucker塑性公设,采用纯简化有效应力和有效吸力这一对双应力变量,建立了考虑吸附水的土水完全耦合的非饱和土弹塑性理论框架,据此获得采用净应力和吸力表示的弹塑性柔度矩阵,用于采用上述本构理论建模时理论模型与土工试验成果之间直接相互验证。
In order to explore the effect of suction between soil and water on the mechanical response of unsaturated soil, the water in soil is divided from its existing environment into the free water which is store in capillary tubes of soil predominantly by the sucking action of liquid surface tension and the adsorbed water which is bound surrounding soil particles predominantly by the absorptive action of matrix electrostatic charge. After the soil particle matrix together with the absorbed water is thought of as soil skeleton phase, the free water is thought of as fluid phase and the gas in soil is thought of as gas phase, respectively, the work expression is obtained for unsaturated soil considering absorbed water. Based on the thermodynamical dissipative theory,entropic flow and entropic product expressions for unsaturated soil in the process of adiabatic deformation are derived from the work expression and local thermodynamic equilibrium assumption. The adsorption equation of adsorbed water in soil is achieved by the thermodynamical adsorption equilibrium theory; and a practical soil-water characteristic curve for adsorbed water is further proposed. Employing the thermodynamical conjugates of entropic product expression together with Drucker's plastic postulate in dissipative space, the soil-water fully coupling elastoplastic theoretical framework of unsaturated soil in consideration of absorbed water is established by virtue of a couple of stress variables named as pure simplified effective stress and effective suction. The flexibility matrix with respect to net stress and suction is obtained from this theoretical framework, which can be used to compare directly theoretical model with experimental results in the application of the above theoretical framework on establishing the practical model.
In order to explore the effect of suction between soil and water on the mechanical response of unsaturated soil, the water in soil is divided from its existing environment into the free water which is store in capillary tubes of soil predominantly by the sucking action of liquid surface tension and the adsorbed water which is bound surrounding soil particles predominantly by the absorptive action of matrix electrostatic charge. After the soil particle matrix together with the absorbed water is thought of as soil skeleton phase, the free water is thought of as fluid phase and the gas in soil is thought of as gas phase, respectively, the work expression is obtained for unsaturated soil considering absorbed water. Based on the thermodynamical dissipative theory,entropic flow and entropic product expressions for unsaturated soil in the process of adiabatic deformation are derived from the work expression and local thermodynamic equilibrium assumption. The adsorption equation of adsorbed water in soil is achieved by the thermodynamical adsorption equilibrium theory; and a practical soil-water characteristic curve for adsorbed water is further proposed. Employing the thermodynamical conjugates of entropic product expression together with Drucker's plastic postulate in dissipative space, the soil-water fully coupling elastoplastic theoretical framework of unsaturated soil in consideration of absorbed water is established by virtue of a couple of stress variables named as pure simplified effective stress and effective suction. The flexibility matrix with respect to net stress and suction is obtained from this theoretical framework, which can be used to compare directly theoretical model with experimental results in the application of the above theoretical framework on establishing the practical model.
引文
[1]COLLINS I F,HOULSBY G T.Application of thermomechanical principles to the modeling of geotechnical materials[J].Proceedings of the Royal Society of London(Series A),1997,453(3):1975-2001.
[2]HOULSBY G T.The work input to an unsaturated granular material[J].Géotechnique,1997,47(1):193-196.
[3]WHEELER S J,SHARMA R S,BUISSON M S R.Coupling of hydraulic hysteresis and stress-strain behaviour in unsaturated soils[J].Géotechnique,2003,53(1):41–54.
[4]BORJA R I,KOLIJI A.On the effective stress in unsaturated porous continua with double porosity[J].Journal of the Mechanics and Physics of Solids,2009,57(8):1182-1193.
[5]李舰,赵成刚,蔡国庆,等.双孔隙结构膨胀性非饱和土功的表达式及其本构模型的理论框架[J].科学通报,2013,58(13):1255-1263.LI Qian,ZHAO Cheng-gang,CAI Guo-ging,et al.Work expression of unsaturated soils with double porosity structure and theoretical framework of its constitutive model[J].China Science Bulletin,2013,58(13):1255-1263.
[6]李如生.非平衡态热力学和耗散结构[M].北京,清华大学出版社,1986:76-106.
[7]ALONSO E E,PEREIRA J M,VANUNAT J,et al.A microstructurally based effective stress for unsaturated soils[J].Geotechnique,2010,60(12):913-925.
[8]SALAGER S,EI YOUSSOUFL M S,SAIX C.Definition and experimental determination of a soil-water retention surface[J].Canadian Geotechnical Journal,2010,47(6):609-622.
[9]FAYER M J,SIMMONS C S.Modified soil water retention functions for all matric suctions[J].Water Resources Research,1995,31(5):1233-1238.
[10]SILLERS W S,FREDLUND D G.Statistical assessment of soil-water characteristic curve models for geotechnical engineering[J].Canadian Geotechnical Journal,2001,38(6):1297-1313.
[11]胡亚元.n次齐次屈服函数相关联流动法则失效的机制研究[J].岩土工程学报,2013,35(2):243-251.HU Ya-yuan.Failure mechanism of associated flow rule for nth homogenous yield function[J].Chinese Journal of Geotechnical Engineering,2013,35(2):243-251.
[2]HOULSBY G T.The work input to an unsaturated granular material[J].Géotechnique,1997,47(1):193-196.
[3]WHEELER S J,SHARMA R S,BUISSON M S R.Coupling of hydraulic hysteresis and stress-strain behaviour in unsaturated soils[J].Géotechnique,2003,53(1):41–54.
[4]BORJA R I,KOLIJI A.On the effective stress in unsaturated porous continua with double porosity[J].Journal of the Mechanics and Physics of Solids,2009,57(8):1182-1193.
[5]李舰,赵成刚,蔡国庆,等.双孔隙结构膨胀性非饱和土功的表达式及其本构模型的理论框架[J].科学通报,2013,58(13):1255-1263.LI Qian,ZHAO Cheng-gang,CAI Guo-ging,et al.Work expression of unsaturated soils with double porosity structure and theoretical framework of its constitutive model[J].China Science Bulletin,2013,58(13):1255-1263.
[6]李如生.非平衡态热力学和耗散结构[M].北京,清华大学出版社,1986:76-106.
[7]ALONSO E E,PEREIRA J M,VANUNAT J,et al.A microstructurally based effective stress for unsaturated soils[J].Geotechnique,2010,60(12):913-925.
[8]SALAGER S,EI YOUSSOUFL M S,SAIX C.Definition and experimental determination of a soil-water retention surface[J].Canadian Geotechnical Journal,2010,47(6):609-622.
[9]FAYER M J,SIMMONS C S.Modified soil water retention functions for all matric suctions[J].Water Resources Research,1995,31(5):1233-1238.
[10]SILLERS W S,FREDLUND D G.Statistical assessment of soil-water characteristic curve models for geotechnical engineering[J].Canadian Geotechnical Journal,2001,38(6):1297-1313.
[11]胡亚元.n次齐次屈服函数相关联流动法则失效的机制研究[J].岩土工程学报,2013,35(2):243-251.HU Ya-yuan.Failure mechanism of associated flow rule for nth homogenous yield function[J].Chinese Journal of Geotechnical Engineering,2013,35(2):243-251.