Xi Zhong Shen’s research while affiliated with Shanghai Institute of Technology and other places

Bank slope seepage field is analyzed by saturated-unsaturated seepage theory under the three times cycle conditions of water level rising and drawdown . The pore water pressure distribution laws of the water level rising period, the stabilization period, the period of decline and decline stable period for every cycle are researched. The result shows soil near slope region is saturated easily after many rounds of water level rising and drawdown, and saturation region gradually increases. Soil phreatic line near slope falls fastly in the drawdown period, away from the slope, phreatic line declines slowly.

Yellow River is a typical wandering channel with large sediment content. Lack of systemic data about composition of riverbed and indexes of mechanical characteristic, the influence of composition and indexes of mechanical characteristic of riverbed was considered difficultly in physical and mathematical models. Mechanical characteristic of soil considered, identification standard of soil layer about riverbed was carried out based on strength resistance of cone tip and the ratio of friction resistance between lateral cone and cone tip, and comparative analysis is worked out with identification standard of indoor geotechnical test. Taking the typical wandering section of river from Baihe to Yiluo outfall as the example, cone penetration tests were carried out and indoor tests were worked out. Firstly, huge data about composition and mechanical characteristic of riverbed are achieved, it shows that the main components of riverbed in lower Yellow River are silty clay, silty loam, sandy loam, sand and so on. Secondly, physical and mechanical indexes of riverbed soil keep strong regularity. Finally, formation cause and change trend are achieved through the basic data of riverbed soil, thus it will improve the development of technology of (Line No. 1) physical model and numerical method for river research (Line No. 2).

Sizing of material flaw is addressed in the multipath scene, and a method is developed to detect an isolated sized flaw and estimate its height based on imaging theory of different path profiles. A signal model based on the multipath higher order reflections of the flaw is built to detect the sized flaw. Multipaths are predicted and identified on the basis of the direct reflection path, which is relatively easy to be identified using the conventional flaw detection techniques. Direct reflection path and combined path are applied to detect the flaw from the top, and multipath w is to detect its bottom of the flaw. Ultrasonic imaging is formed and synthesized by all the identified multipaths, which shows the size of the material flaw. Simulations and experimentations demonstrate that the flaw sizing can be calculated utilizing the time-of-arrivals of the multipath signals.

Evaluation indexes (monitoring value) set in safety evaluation of dike, it was difficult in conforming the range of evaluation indexes, and could not reflect characteristic of outburst destroy. Catastrophe theory is a kind of mathematical method that problems of transition, discontinuity, and abrupt qualitative change based on analysissitus, problems about how a system of continuous quantitative change to evolving into jumping qualitative change can be analyzed. Firstly, the relation between deformation of dike with components of water pressure, temperature and time effect is analyzed, subdivision lemma of cusp catastrophe theory is cheesed, expression of potential formula on horizontal deformation is carried out based on influence of factor of time, water pressure and temperature. Moreover, normal form of catastrophe is advanced and critical rules of dike safety are put forward, evaluation model based on catastrophe theory is established. Finally, the model is validated with dike of Yellow River. Analysis shows that evaluating conclusion of the model is as the same as the practice, and it can not only reflect outburst destroy character of dike, but also evaluate safety degree in quantity, thus the model is good in adaptability and precision.

Accurate in apparatus, complex in operation, expensive in fund and plentiful in time, test of unsaturated soil is difficult. Influence of status of dry and wet and degree of compacting was not considered generally when Duncan-Chang model was be used to unsaturated soil. With parameters of model served as constants, it was not consistent with the practice that parameters would be changed with saturation and water content and its application would be limited. General triaxial tests of drainage and consolidation about dry density and water content combined are carried out, influence of relation between stress and strain about clay is discussed, mathematical equations of parameters of Duncan-Chang model are established, thus modified Duncan-Chang E-B model of unsaturated clay is carried out that influence of dry density and saturation can be considered. From study we can see, on the one hand, characteristics of stress and strain about unsaturated clay are influenced obviously by saturation and dry density, the main parameters of E-B model keep close correction with dry density and saturation, and the both mutual effect can be expressed by multiplication. On the other hand, status of compacting and process of gradual change from dry to wet can be described with modified E-B model. Thus it will be more complete in factors considered, inosculate in practice, and convenient for use.

Ultrasonic signature of flaw is studied in the multipath scene, and a method is developed to localize the flaw by only single mono/bi-static measurement. A signal model based on the concept of multipath is built to construct flaw position, of which multipath scenarios are reviewed for signature of flaw depth. Multipath scenarios may be identified by direct path, which is relatively easy to be detected. Algebraic solution is proposed to solve the multipath equations to obtain the position of the flaw depth. Experiments show that the solution of the flaw depth is valid.

Difficult in soil-water characteristic curve achieved, existence of non-uniqueness and indistinct in influence of unlinear deformation characteristics of soil about density and water content, deformation characteristics of unsaturated soil were studied difficultly with general triaxial test, thus direct application of unlinear Duncan-Chang model in unsaturated soil was restricted. General triaxial tests with combined dry density and water content are carried out, changing rules of parameters of Duncan-Chang model are summarized, mathematical functions between dry density, saturation and parameters of the model are established. Analysis shows that deformation characteristics of unsaturated clay are influenced obviously by saturation and dry density. Among them, the larger the saturation, the higher strain becomes under the condition of the same dry density and main stress difference, and the less the dry density, the higher strain becomes under the condition of the same saturation and main stress difference. Moreover, the main parameters of Duncan-Chang model keep close correction with dry density and saturation, and the both mutual effect can be expressed by multiplication. This shows that mechanical characteristics of unsaturated soil can be studied with general triaxial test, thus it will be used easily in project.