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The state of zero effective stress is a situation at which the effective stress of saturated sand decreases to zero in the process of liquefaction. In the state of zero effective stress, sand particles suspend in water and the foundation is vulnerable to much large lateral deformation. The state of zero effective stress can be achieved through dynamic loading tests, but the obtained state is difficult to sustain a steady situation. To simulate the suspended sand in water under fully liquefied condition, plastic sand, characterized by small specific gravity, is used instead of quartz sand to build an inclined foundation. Salt water with similar density is used to pass in slowly near bottom of the foundation. As observed in tests, the plastic sand is able to suspend in sodium chloride solution (salt water) of a specific density and thus this model can be used to simulate the lateral spreading of a foundation under zero effective stress state. Lateral deformation occurs within a certain depth beneath the ground and the magnitude increases from the bottom up, showing nonlinear behaviors. This paper presents a physical modeling approach for achieving the state of zero effective stress under static laboratory condition.

Low temperature stress is a worldwide major abiotic stress affecting plant yield and quality.Plant physiological ecology of cold hardiness research is a more active and fast growing field.In this paper,advances of study on the mechanism of improving plant cold hardiness was reviewed.Scientific research and production practice have showed that meteorological factors and/or factors of plant itself are the key factors affecting plant cold hardiness;the former is mainly temperature,photoperiod and water;while the latter is mainly plant genetic basis,growth period,development level and cell antioxidant capacity under low temperature stress.Ensuring fully expression of genes of plant cold hardiness is of important significance on improving plant cold hardiness.Genetic mechanism and regulation of plant cold hardiness are mainly through 5 paths to achieve,respectively: the rich diversity of low temperature induced plant proteins;low temperature transcription factor DREB/CBF can simultaneously control a plurality of expression of genes cold induced in plants;interactions of DREB/CBF and cofactor regulate expression of downstream genes;Ca2+,ABA and protein phosphorylation regulate gene expression induced by low temperature in the upstream;and the expression of genes of unsaturated fatty acid synthase.Genetic engineering to improve plant cold hardiness has been significant progress,but from the industrialization has still a lot of pioneering work to do.Currently,genetic engineering of improving plant cold hardiness are mainly through the introduction of regulatory genes and/or functional genes,the latter is mainly the introduction of genes related to osmotic stress resistance,genes of antifreeze proteins,genes of fatty acid desaturation metabolism key enzyme,genes of SOD and other antioxidant system component,as well as genes involved in the regulation of plant hormone.Agricultural and forestry technologies to improve plant cold hardiness have important practical value,many of them are of profound scientific mechanism,im which we focused on the mechanism of 5 main technologies improving plant cold hardiness,respectively: cold hardiness breeding,grafting,cold acclimation,the coupling of water and fertilizer and chemical induction.The prospect of future research on improving cold resistance of plant was discussed.