非饱和花岗岩残积土粒间联结作用与脆弹塑性胶结损伤模型研究

Research on soil particle joint function and brittle-elastoplastic cement damage model of unsaturated granite residual soil

非饱和花岗岩残积土主要为铁质胶结,遇水后强度急剧降低,结构性强,显示出脆弹塑性损伤破坏特点,其粒间联结作用正是其结构性和脆弹塑性损伤破坏的核心问题。论述了非饱和土的粒间联结作用,将其分为接触联结和非接触联结两类,这两种联结在粒间相互作用上都表现为吸力的作用,即由湿吸力、可变结构吸力组成的粒间吸力。非饱和花岗岩残积土铁质胶结为主的接触联结作用,加上其砂粒、黏粒等各级粒度成分混合,致使粒间联结作用遇水或扰动后变化大,导致力学性质上的脆性显著。通过理论推导,给出了可变结构吸力与土体堆积方式、干密度、孔隙比、含水率/饱和度的定量计算公式,并由试验验证了计算公式的合理性。进而从游离氧化铁胶结是非饱和花岗岩风化残积土显示脆弹塑性的根本原因出发,基于堆砌体模型思想,采用孔隙比与结构脆性参数构建损伤过程函数,建立了可反映非饱和花岗岩残积土脆弹塑性胶结损伤的理论模型,通过试验验证表明,所建模型能很好地反映非饱和花岗岩残积土特有的应力-应变关系,从理论上较好地解释了花岗岩残积土遇水或扰动后易破坏的机制。

Unsaturated granite residual soil is mainly ferruginous cement, its strength decreases sharply in water, structural significant, showing brittle-elastoplastic damage characteristics, whose soil particle joint function is the core problem of structure and brittle- elastoplastic damage. The unsaturated soil particle joint function is discussed; it is divided into contact and non-contact joints, and these two kinds of joints are expressed as suction effects in soil particle intergranular interactions, that is the suction between grains composed of variable structure suction and wet suction. For unsaturated granite residual soil, particle joint function should be paid more attention. Unsaturated granite residual soil’s contact joint is dominated by ferruginous cementation and all levels of granularity composition mixtures as sand, clay and so on; they cause the suction between grains changing greatly in water or disturbance, resulting in the properties of the brittleness in the mechanics of unsaturated granite residual soil. Then through theoretical derivation, by referencing coordination number, the Smith formula, and the Fisher formula in mineralogy, crystal powder mechanics and engineering, quantitative calculation formula of variable structure suction and the soil accumulation mode, dry density, void ratio, water / saturation are given; and the rationality of the calculation formula is verified by tests. Then we research and realize that free iron oxide cement is the fundamental point of granite residual soil’s property of brittle-elastoplasticity, so a masonry model is used; and then void ratio and structure parameter are applied to construct the brittle damage process function; a theory model which can reflect the damage of unsaturated granite residual soil elastoplasticity is established. Through the comparison of calculation and experiment results. The results show that the model established above can well reflect the unique stress-strain relationship of unsaturated granite residual soil. It can explain well the mechanism of unsaturated granite residual soil which is easily destroyed in water or disturbance according to theory.