Data mining in deductive databases using query flocks

Data mining can be defined as a process for finding trends and patterns in large data. An important technique for extracting useful information, such as regularities, from usually historical data, is called as association rule mining. Most research on data mining is concentrated on traditional relational data model. On the other hand, the query flocks technique, which extends the concept of association rule mining with a ‘generate-and-test’ model for different kind of patterns, can also be applied to deductive databases. In this paper, query flocks technique is extended with view definitions including recursive views. Although in our system query flock technique can be applied to a data base schema including both the intensional data base (IDB) or rules and the extensible data base (EDB) or tabled relations, we have designed an architecture to compile query flocks from datalog into SQL in order to be able to use commercially available data base management systems (DBMS) as an underlying engine of our system. However, since recursive datalog views (IDB's) cannot be converted directly into SQL statements, they are materialized before the final compilation operation. On this architecture, optimizations suitable for the extended query flocks are also introduced. Using the prototype system, which is developed on a commercial database environment, advantages of the new architecture together with the optimizations, are also presented.     

基于HSS模型隧道近接群桩基础施工影响分析

依托盾构隧道近接侧穿群桩工程建立三维数值分析模型,土体采用小应变硬化(HSS)模型,参数取值借鉴已有研究成果并根据监测位移数据反演,同时考虑土体开挖、衬砌拼装以及盾尾同步注浆等一系列施工工艺措施,并将模拟结果与监测数据进行对比验证,研究了不同工况下地表沉降的形态分布、群桩桩基变形及基桩结构受力,同时考虑地表位移对等代层厚度的敏感性。结果表明:HSS模型能有效预测隧道近接侧穿高架桥桩引起的变形,模拟结果与监测值较吻合; 隧道开挖引起土相对桩产生了滑移,地表沉降及桩身竖向位移在中心线前后各1D(D为管片外径)范围内随推进步数的增加而不断增大,且增加幅度明显减小; 两线推进地表沉降具有叠加效应,最大沉降量增幅达76.8%; 隧道与基桩水平距离越近,引起基桩沉降变化越大,两线推进基桩桩顶沉降增幅达134%; 群桩中各排桩的水平位移变化趋势基本相同,且同排桩的水平位移值相差不大,由于群桩遮挡效应,水平位移值由大到小依次为前排桩、中排桩、后排桩; 桩身水平位移主要在盾构中轴线2.5D范围内,桩身最大水平位移均出现在隧道中轴线附近; 群桩中同排桩桩身附加弯矩及附加轴力沿桩身分布规律相同,桩身最终附加受力与其距离隧道远近有关; 随着注浆充率β的增大,等代层厚度及地表沉降呈线性减小; 穿越段采取的施工工艺方案是有效的,经估算附加弯矩及轴力对桩基承载力的影响在容许范围内。     

Investigation of unsaturated frozen soil behavior: Phase transformation state,post-peak strength,and dilatancy

In this study, a database of triaxial compressive tests on unsaturated frozen soils is compiled to investigate the mechanical behavior that has not been considered in previous studies. The results for the stress-strain volume changes are presented first. Then, the physical mechanisms that might control the deformation of unsaturated frozen soils, namely, volumetric compression and frictional sliding, are used to interpret the changes in volume and deviator stress during the tests. The relationship between the compression rate due to the mean stress and the dilation rate due to shearing determines the changes in sample volume and shear stress with an increasing axial strain. The test results indicate that confining pressure and temperature significantly affect the phase transformation state, the post-peak strength, and the maximum dilation ratio. A higher post-peak strength ratio is observed in tests performed at higher confining pressure or under a higher temperature. As the confining pressure is increased, the shear stress at the phase transformation state initially increases and then decreases or stabilizes. However, the maximum dilation ratio decreases considerably and tends to reach zero after a certain confining pressure is reached. Both the deviator stress at the phase transformation state and the maximum dilation ratio are higher under a lower temperature given constant confining pressure. Ice cementation and pressure melting are attributed to the specific features of frozen soils compared to those of unfrozen soils. This paper provides new insights into the mechanical behavior of frozen soils.     

Study on the relationship between the shallow ground temperature of embankment and solar radiation in permafrost regions on Qinghai–Tibet Plateau

The temperature field of permafrost embankments is a key factor to determine the embankment stability. On the basis of observed climate data and field-temperature values in Beiluhe on the Qinghai–Tibet Plateau, this paper uses statistics methods to set up a regression equation between the temperature at shallow ground depth (0.5 m) and the net radiation on embankment horizontal surface. There is a good linear relation between the temperature and the net radiation after the phase difference is removed. Moreover, an empirical formula consisting of the shallow-ground temperature of (0.5 m) and the direct solar radiation is proposed. It is also suitable for the area having high elevation at the Beiluhe site. These formulas combining with the law of documents and materials suggest that there exists an obvious linear relation between the temperature on horizontal surface and the direct solar radiation. However, there is hardly linear relation between the temperature and the direct solar radiation on embankment slopes. The key factor is that the railway embankment slope has a relatively heavier gradient. The slopes with heavier gradient have different heat transfer characteristic during a specific year. In summer, the sun is shining straight on the ground, which results in a relatively lower direct solar radiation on slopes; however, because of diffuse radiation and higher temperatures of the horizontal surface, temperatures on slopes are relatively higher. In winter, the direct solar radiation on shady slopes is even zero, meaning that there is almost no direct solar radiation. Thus, the relations between the temperature and the direct solar radiation on slopes are more complicated.     

Application of a co-continuous composite model of effective thermal conductivity to ice–air systems

Effective thermal conductivity measurements were performed for two ice–air systems (ice chips produced by a commercial ice-maker and synthetic snow) using a transient comparative technique. These systems were chosen because the ice fraction could be controlled, thereby de-coupling the problems of ice fraction and thermal conductivity prediction. None of the commonly used simple effective thermal conductivity models (specifically the Series, Parallel, two forms of the Maxwell–Eucken and Effective Medium Theory models) provided adequate prediction accuracy over the full range of ice fractions in the experimental data. The best predictions were provided by a composite model that combined the Effective Medium Theory structure and the recently developed co-continuous structure.     

In-situ pressuremeter test in warm and ice-rich permafrost

In order to investigate the in-situ mechanical behavior of warm and ice-rich frozen soils, a series of pressuremeter tests were carried out in permafrost regions on the Qinghai-Tibetan Plateau. Based on the test results, the relationship between stress and strain was obtained using Ladanyi's theory, and it can be described by a hyperbolic model. Moreover, two critical mechanical parameters, ultimate shear strength and initial shear modulus, for each test were deduced from the hyperbolic model. The shear strength increases linearly with decreasing temperature regardless of the water content, while the variation of the shear strength with the water content presents an exponential tendency. Comparing the results of pressuremeter tests with the results of triaxial test and uniaxial test, it can be found that the strengths obtained from pressuremeter tests are always greater than those of indoor tests. In the earlier stage of the pressuremeter test, the circumferential stress is reduced by the same increment as the radial stress increases. However, when the radial stress reaches a certain value, the circumferential stress increases gradually and even becomes a compressive stress.     

Theoretical analysis of coal stockpile self-heating

This paper theoretically analyses the problem of coal stockpile self-heating under free convection (no wind) conditions. Scale analysis has been used to drive expressions for the stockpile temperature and inflection point (when the stockpile is completely dry) as functions of the key parameters including the coal type, moisture content, and particle diameter as well as the ambient air temperature. Theoretical predictions are then successfully compared with experimental data and CFD simulations results available in the open literature.     

An improved statistical damage constitutive model for warm frozen clay based on Mohr–Coulomb criterion

There are many microdefects distributed randomly in frozen soil, which will lead to great uncertainty and randomness of mechanical properties and behaviors under applied load, therefore, it is more scientific to study stress–strain relationship of frozen soil by stochastic method instead of deterministic way. For the warm frozen clay and warm ice-rich frozen clay, a stochastic damage constitutive model has been proposed on the foundation of a large number of experimental data, in which the axial strain is regarded as random variable. In this paper, according to these experimental data under three temperature conditions (− 0.5 °C, − 1.5 °C and − 2.0 °C) and the above research results, the strength of soil element is selected as random variable and an improved statistical damage constitutive model is deduced, and in this new model, the Mohr–Coulomb failure criterion is also used to judge whether the soil element is damaged. Finally, compared with original model, it is found that the new improved model can better describe the experimental data and reflect deformation characteristics. Especially, when the stress reaches its peak value, the experimental data and new theoretical curves overlap with each other.     

Study of heat and moisture transfer in soil with a dry surface layer

Mathematical model for describing simultaneous heat and moisture transfer in the porous soil with a dry surface layer was developed by using the volume-averaging method. Numerical simulation was conducted to investigate water evaporation, transient distributions of temperature and moisture in the porous soil at environmental conditions, which might be useful for agricultural application. In order to validate the mathematical model and numerical method, an experiment was conducted under natural environmental conditions. An additional experiment was conducted in a closed-loop wind tunnel to investigate the temperature effect on soil moisture transport. Theoretical and experimental results indicate that the dry surface layer has an important effect on heat and moisture migration in soil and the influence of temperature on moisture transport in unsaturated soil is significant.