Cracking Law Of Landfill Compacted Clay Cover System

Aiming at the problem that the landfill compacted clay cover system isvulnerable to appear desiccation cracking in drought or semi-arid area, develop thecompacted clay experimental research on the expansion and the contraction, thedesiccated cracking, and hot-water transmission tests in the cracking process, andreveal the cracking mechanism of the landfill compacted clay cover system. Basedon the cracking dynamic mathematical model of compacted clay cover system, andpredicte the cracking law of landfill compacted clay cover system through thesimulation. The research has the very important theoretical significance andapplication value for reducing or avoiding the cracking destruction of the landfillcover system, and for the design and the construction of the landfill cover system.Some conlusions can be shown from the compacted clay expansion and thedry-shrinkage tests: when the initial moisture content is0.21and the dry density is1.50and1.65g/cm3, the compacted clay expansion is much smaller, and theexpansion changes as time with "S" type; The dry-shrinkage deformation of thecompacted clay has significant anisotropy, and the radial shrinkage has the largerimpact on the volume contraction; The shrinkage ratio grows exponentially with theincrease of the initial moisture content, but reduces linearly with the increase of thedry density.Compacted clay cracking test shows that the dry-wet cycle effect has thesignificant influence on the compacted clay cracking; and the part of compactedclay cracks appears to be healing in the early of wet, the cracks will emerge again,and is significantly more than the previous dry-wet cycle in the end of dry-wetcycle; The initial moisture content and the dry density have obvious effect on thecompacted clay cracking, and the compacted clay cracks are least under thecondition of the best dry density (1.65g/cm3) and the optimal initial moisturecontent (0.21), and the cracking factor is0.06after four wet-dry cycles.Heat and water vapor migration model test in the cracking process shows thatthe surface cracking of the clay column is obvious at the60℃heat source after16days later, the cracking factor is0.09, and the cracking depth is about8.2cm. In theearly of heating, the clay temperature rises fast, and water loses severely, but theduration time is short; The temperature rising speed is obviously decaying overtime and it is long water-loss process.Based on the heat conduction equation, water vapor transporting equation andforce balance equation, establish the cracking kinetic mathematical model of thelandfill compacted clay cover system. Considering the surface temperature changesand the moisture loss, simulate to analyse the cracking rule of the landfill compacted clay cover system by using the finite element software COMSOL. Somecalculation results are shown: the temperature decreases gradually from the top tothe bottom in the landfill compacted clay cover system, the moisture migratessuccessively from the bottom to the top, the moisture content also decreases, andthe cracks turn up and the tensile stress concentration occurs in the crack tips. Thenumber of the cracks gradually increases over time and the cracks extend in thelongitudianl direction, and the settlement displacement with more cracks is largerbut the displacement with less cracks occurs lifting phenomenon; The region ofcrack tip stress concentration moves down, and the stress concentration region ofcracks occurs in the middle of adjacent cracks stress areas; The clay temperatureincreases rapidly and water loses serious near the cracks.