| At present,the collapse assesment and treatment of loss canal foundation is still based on the maximum collapse concept,which lags behind current engineering practice.In this paper,the assessment and treatment methods of collapsible loss foundation were explored,based on possible collapse design thoughts and methods.The research abstracts is as follows:(1)The trial research on humidification deformation behaviors of undisturbed loess was carried out.Firstly,the concept of humidification level has been introduced to describe the moisture condition of soil.Secondly,taking the loess from yili,xinjiang as the studied object,stepped wetting tests under a side-limit condition were carried out.The humidification deformation coefficient δup,matric suction s,as well as the coeffcient of earth pressure at rest K0 of the corresponding humidification level Sw under different vertical pressures was measured.A humidification deformation constitutive model under a side-limit condition was established by analyzing the relevant relationships between δup and Sw.A soil water characteristic curve model was put forward by analyzing the relevant relationships between s and Sw.The expressions of the coeffcient of earth pressure at rest were built by analyzing the relevant relationships between K0 and Sw.Then,taking the loess from zhangqiao,shanxi as the studied object,stepped wetting tests under a tri-axial constant stress ratio condition were carried out.The humidification volumetric strain εvz and shearing strains εrz of the corresponding humidification levels under different tri-axial stress states was measured.The humidification deformation constitutive model under tri-axial stress conditions was established,based on the mathematical description of the correlativity between Sw and εvz,Sw and εrz.Lastly,the field immersion tests were carried out on loess canal foundation in yili.During the field immersion tests,the deformation field and moisture field were measured,and the collapsible deformation law during soaking process was revealed.(2)The centrifugal model tests on the humidification deformation of loess foundation were carried out.Taking the typical stratified undisturbed loess form yili canal collapsible loess foundation as the studied object,three groups of centrifugal model tests were carried out,with the saturability of 40%,80%and 100%respectively.Layered deformation observation dots and soil pressure sensors were installed in the model,to simulate the layered deformation characteristics and earth pressure change law of the actual foundation,during the humidification process under gravity stress.On the basis of the centrifugal model tests on humidification deformation of loess foundation,using the correction factor β0 as a bridge,a new experimental method for loess collapsibility using centrifugal model tests was proposed.The good agreement in the experimental study using centrifugal model tests and the field immersion tests showed that the proposed method can be used as an effective method in measuring loess collapsibility.(3)A new assessment method for loess canal foundation was proposed.According to the characteristics of cannel engineering,a new assessment method for loess canal foundation collapse,based on possible collapse deformation,was proposed,using the permeate theory of unsaturated soil and the humidification deformation constitutive model established in this paper.According to"Standard for engineering technique of seepage prevention on canal(GB T 50600-2010)" and"Design code for anti-frost-heave of canal and its structure(SL 23-2006)",standards on dividing collapsible grade and the important class of canal foundation were set up based on the possible collapse concept,considering the reality that the plate membrane structure is widely used in present canal engineering.The new assessment method was used to conduct a collapse assessment on a large diversion canal engineering of yili,xinjiang.The result shows that the method is reasonable and available. |
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