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Study on Bearing Capacity of Foundation Soil about Power Transmission Project under Heavy Snow Conditions in Southern China

Author: WangYongZhong
Tutor: HuXinLi；AiChuanJing
School: China University of Geosciences
Course: Geotechnical Engineering
Keywords: Extreme snow disaster Freeze-thaw test Shear strength index Foundation soil Carrying capacity Numerical Simulation
CLC: TU470
Type: Master's thesis
Year: 2011
Downloads: 34
Quote: 0
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Abstract

In early 2008, in most parts of southern China suffered a once-in-a-century extreme snow disaster, this time, the long duration of the snow disaster, the impact of the wide range of harmful levels deep are rarely seen in history. Large-scale, high-intensity snowfall and melting snow caused hundreds of geological disasters, more dramatic impact on the safe operation of the southern grid. According to incomplete statistics, the the the inverted tower in the 500kV main network line has reached more than 20, the base of the inverted tower more than 100 below 500kV power grid by the wider impact was otherwise not run properly substations, more than 200 billion yuan of direct economic losses . Preliminary engineering design standards did not consider this factor of extreme snow disaster, and is currently China is still a lack of a response southern extreme snow disaster governance system, the lack of a well-established engineering control measures and emergency measures, combined with bursty extreme snow disaster that led to huge losses in the power engineering facilities in the extreme snow disaster. At present, the region of southern China, the achievements of the foundation soil bearing capacity of the power transmission project in the extreme snow conditions relatively small, northern research may not be suitable for the environmental conditions at the southern extreme snow, therefore, an urgent need for power transmission project bearing capacity of the foundation soil of the southern region under conditions of extreme snow disaster. Firstly, starting from the soil freezing and thawing test, freeze, thaw process and the freezing and thawing of the soil under the shear strength index variation, focusing on analysis of different water content, temperature, and freeze-thaw cycles on soil anti- shear strength index impact factor of the water content, temperature, and freeze-thaw cycle, the bearing capacity factor in the specification of design of building foundation bearing capacity of foundation formula, based on the limit equilibrium theory and based on the elastic-plastic theory foundation bearing capacity; then introduced capacity coefficients in the formula are modified to obtain a freeze and thaw conditions and freezing and thawing, the foundation bearing capacity correction formula; numerical analysis of the ultimate bearing capacity of strip footings in the freezing process, the analysis of the bar shaped shallow foundation under different temperatures and load deformation and failure of the law, and the numerical solution of ultimate bearing capacity; undermine research by the deformation of the transmission Taki based transmission Taki at different temperatures and different icing load in the deformation and mechanical characteristics. The research results obtained are as follows: (1) through the soil to freeze, thaw and freeze-thaw cycle test, analysis of freeze, thaw process and the freezing and thawing of the soil under the shear strength index variation of: ① normal temperature, the heavy Plastic soil c and φ values ??decrease with increasing water content without disturbing the soil sample c the φ value than the same water content reshape soil samples; ② in the freezing process, found in soil inherent in the freezing temperature; regardless of undisturbed soil sample or remodeling soil sample c, φ value with decreasing temperature increases, the temperature is higher or lower than the freezing temperature of the soil, c, φ value amplitude; remolded ③ for salty dream line under its frozen state c the φ values ??will reduce with increasing water content. Water content c values ??are the most obvious, is bounded to the middle of the water content can be divided into two stages; when the water content is less than the middle of the water content, the c value increases with the lowering of the freezing temperature; moisture content exceeds the intermediate moisture content, the value of c will decrease as the freezing temperature decreases; For remolded Qujiang line, with the water content increases, c, φ, the value of each temperature sample are first increased large and then decreases; same water content, with the lowering of the freezing temperature of sample c, φ values ??are increasing; ④ during the thawing process, disturbed soil and remodeling soil sample c values in decreases, φ is slowly increasing. , With the thawing temperature changes due to the presence of freezing temperature, when the temperature is below the freezing temperature, soil c, Φ values ??change little; However, when the temperature is higher than the freezing temperature of the frozen soil to ice phase change violently, soil not freeze the water content increased, resulting in ten c, φ value is a significant change in: (5) freeze-thaw action strongly changed ten structure, thereby changing its mechanical properties. Freeze-thaw the role Houtu structure become loose soil particles shape becomes broken, tend irregular, causing soil skeleton structural shift its entire force system changes. Determination by the trial, after freezing and thawing soil c value decreases, φ value increases, the shear strength of the soil as a whole decreases. (2) of the freeze, the process of thawing and freezing and thawing of foundation soil c, the φ value changes in law and influencing factors of bearing capacity of foundation ten based on the method of analysis of the bearing capacity of the foundation soil freezing and thawing conditions: (1) the introduction of impact factor T (temperature), of body c freeze - thaw process Middle-earth, the φ value repair only, get the bearing capacity factor correction in the freeze - thaw process, summed up the modified design of building foundation specifications bearing capacity factor proposed foundation bearing capacity formula and the modified Terzaghi ultimate bearing capacity formula; ② introduction of impact factor n (freeze-thaw cycles), c, φ value of the freezing and thawing of soil under the amendment, correction correction formula based on the elastic-plastic theory foundation bearing capacity; ③ mountain different freezing temperatures, the foundation bearing capacity and room temperature under different thawing temperature foundation soil bearing capacity of the ratio between the relational table; ④ were calculated in accordance with the modified bearing capacity of foundation formula come to the relationship between moisture content and the foundation of ten carrying capacity at different temperatures; ⑤ draw a relationship between the freezing and thawing times n foundation soil bearing capacity. (3) by the numerical analysis of ultimate bearing capacity of strip footings freezing process, analyze the deformation of the strip footings damage law and solving for the numerical solution of ultimate bearing capacity of foundation soil: ① temperature deformation little effect, the main factor is the upper load. Same temperature, as the upper load increases, the maximum amount of displacement of the substrate soil, the maximum shear stress is increased, when the load is increased to a certain critical value, the the maximum HO shift amount of the base soil suddenly increased. The maximum shear stress is reduced, the maximum depth of the plastic zone is more than 1/3 of the width of foundation, can be considered the foundation soil shear failure occurred; ② numerical simulation base settlement with loads of soil between the PS curve can be obtained numerical solution of the ultimate bearing capacity of the foundation soil at different temperatures, bearing capacity of the foundation through the numerical solution with the use of freeze-thaw conditions look correction specification formulas, and corrections Terzaghi ultimate bearing capacity formula of foundation soil bearing capacity values ??compared analysis, ultimate bearing capacity obtained by numerical simulation method has certain reliability, and further amended foundation bearing capacity formula in freeze-thaw conditions have a higher rationality and reliability. (4) numerical simulation of the transmission tower foundations extreme snow and ice environment, analysis of deformation and failure of the law of surface temperature and ice loads on transmission Taki impact: the ① Icing deformation load for Taki certain; in prerequisite of the model at the bottom boundary temperature, the surface temperature changes in for Taki stress and deformation of the rock mass are more significant with the impact, but its temperature drops to a certain level, the deformation and stress are gradually getting in stable; ② the left upper Taki vertical load and horizontal wind load, Taki horizontal displacement change is very obvious, two Taki force is extremely uneven, the maximum displacement Mountain Taki's left side minimum displacement appear in the right side of the tower base foundation deformation and failure potential sliding surface, and can display the largest settlement in the vertical direction; Taki appeared in the middle of two Taki position; ③ Taki load and wind load common under the base of the tower and the basis of the contact point of the mountain now obvious stress concentration. In the Kentucky foundation near the bottom, and silty clay with strong weathered sandstone contact surface are varying degrees of stress concentration, and with the reduction of the surface temperature, stress concentration with a significant expansion of the trend. (4) Taki foundation stiffness, the resulting strain is small, while the base near the soil deformation strain maximum strain Mountain is now near the top of the foundation. And clay and silty clay layer mechanical strength, small deformation modulus, large deformation, to produce ground deformation horizons. The results of this research can provide the scientific foundation for our the southern extreme snow and ice environment 12 bearing capacity analysis and calculation theoretical basis. Research-rich southern region in the extreme snow and ice conditions, geological disasters processing technology and design theory, can directly guide the projects under construction in the southern region of extreme snow and ice conditions.

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