本文選題：多年凍土　切入點(diǎn)：群樁　出處：《蘭州交通大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：多年凍土在我國的東北以及青藏高原等地區(qū)分布廣泛,多年凍土地區(qū)建筑物基礎(chǔ)的長期承載性狀是保證寒區(qū)建筑施工與運(yùn)營安全的基石,而我國的多年凍土性質(zhì)復(fù)雜,凍土地基中基礎(chǔ)的承載力受凍土溫度、地質(zhì)條件、凍土類型以及基礎(chǔ)形式等各種因素的影響。樁基礎(chǔ)有著承載力大適用性廣,施工簡便,對地溫的擾動(dòng)較小等優(yōu)點(diǎn),凍土區(qū)的建筑物基礎(chǔ)多采用樁基礎(chǔ)。但是由于凍土性質(zhì)的復(fù)雜,分區(qū)的多樣化,對多年凍土地區(qū)樁基礎(chǔ)特別是群樁基礎(chǔ)的研究沒有普通土那樣完善。而且由于凍土區(qū)群樁基礎(chǔ)無法進(jìn)行現(xiàn)場載荷試驗(yàn),而室內(nèi)模型試驗(yàn)又很難模擬凍土中群樁復(fù)雜的工作狀態(tài),因此進(jìn)行數(shù)值模擬分析是十分有意義的。本文先回顧了一些以往對寒區(qū)工程樁基礎(chǔ)的研究,對受豎向荷載下群樁基礎(chǔ)的基本工作機(jī)理進(jìn)行了闡述。詳細(xì)的介紹了大型有限元分析軟件Midas/GTS,并介紹了數(shù)值模擬的有限元模型,計(jì)算單元、接觸單元以及本構(gòu)模型的選取。采用此軟件進(jìn)行三維可視化建模,通過對青藏高原昆侖山埡口的一例單樁承載試驗(yàn)進(jìn)行了建模分析,數(shù)值模擬分析得到的結(jié)論與現(xiàn)場試驗(yàn)實(shí)測值滿足工程誤差需要,驗(yàn)證了數(shù)值模擬分析參數(shù)選取的準(zhǔn)確性以及此有限元軟件對凍土樁基分析的可行性,然后建立了多種工況下單樁和群樁的數(shù)值模型,分析了不同工況對多年凍土區(qū)單樁以及群樁基礎(chǔ)的承載性狀的影響。本文選取了三種不同凍土溫度的的土參數(shù),分別建立了10m樁長三種不同樁徑的單樁模型以及15m樁長1m樁徑的四種不同樁距的2×2群樁和梅花樁群樁三維模型,對凍土溫度和樁徑對單樁承載特性的影響以及樁數(shù)、樁間距對群樁基礎(chǔ)的影響進(jìn)行了研究,主要分析了樁基礎(chǔ)受豎直方向荷載下的沉降、軸力、樁端阻力以及樁側(cè)凍結(jié)力的變化,探討了群樁的群樁效應(yīng)、破壞特征、破壞方式以及樁側(cè)凍結(jié)力的發(fā)揮過程。從中總結(jié)出多年凍土地基樁基礎(chǔ)增大樁徑以及降低凍土溫度可以顯著提高承載力并且減少沉降;一定范圍內(nèi)群樁樁距的增大可以減少沉降,有限的提高群樁承載力;在不改變樁距的情況下增加樁數(shù)對凍土中樁基承載力提高不明顯以及會(huì)增大沉降等結(jié)論。并且證明了有限元Midas/GTS對凍土中樁基受力模擬的可行性。
[Abstract]:Permafrost is widely distributed in Northeast China and Qinghai-Tibet Plateau. The long-term bearing behavior of building foundation in permafrost region is the cornerstone to ensure the construction and operation safety in cold region, but the permafrost is complex in nature in our country. The bearing capacity of foundation in permafrost foundation is affected by various factors, such as temperature of frozen soil, geological condition, type of frozen soil and form of foundation, etc. Pile foundation has many advantages such as wide applicability of bearing capacity, simple construction, small disturbance to ground temperature, etc. The foundation of buildings in permafrost regions mostly adopts pile foundation. However, due to the complexity of frozen soil properties, the diversity of the zoning, The research on pile foundation in permafrost region, especially pile group foundation, is not as perfect as ordinary soil, and because pile group foundation in permafrost region can not carry out field load test, it is difficult to simulate the complex working state of pile group in frozen soil by indoor model test. Therefore, it is very meaningful to carry out numerical simulation and analysis. In this paper, some previous researches on engineering pile foundation in cold region are reviewed. The basic working mechanism of pile group foundation under vertical load is expounded, the large finite element analysis software Midas / GTS is introduced in detail, and the finite element model and calculation element of numerical simulation are introduced. The selection of contact element and constitutive model. By using this software, a single pile bearing test in Kunlun Mountain pass of Qinghai-Xizang Plateau is modeled and analyzed. The conclusion of numerical simulation analysis and the measured value of field test meet the need of engineering error. The accuracy of parameter selection of numerical simulation analysis and the feasibility of this finite element software for the analysis of frozen soil pile foundation are verified. Then, the numerical models of order pile and pile group under various working conditions are established, and the influence of different working conditions on the bearing behavior of single pile and pile group foundation in permafrost region is analyzed. The soil parameters of three kinds of frozen soil temperature are selected in this paper. Three kinds of single pile models of 10m pile length and three different pile diameters are established, and four kinds of 3D models of 2 脳 2 pile group and plum blossom pile group with different spacing of 15m pile length 1m pile diameter are established respectively. The effects of frozen soil temperature and diameter on the bearing characteristics of single pile and the number of piles are also discussed. The influence of pile spacing on pile group foundation is studied. The variation of settlement, axial force, pile tip resistance and pile side freezing force under vertical load of pile foundation are analyzed, and the pile group effect and failure characteristics of pile group are discussed. It is concluded that increasing pile diameter and decreasing frozen soil temperature can significantly increase bearing capacity and reduce settlement of pile foundation on permafrost foundation. The increase of pile spacing in a certain range can reduce the settlement and improve the bearing capacity of pile group. Without changing the pile spacing, the increase of pile number is not obvious to the bearing capacity of pile foundation in frozen soil and will increase the settlement, etc. The feasibility of finite element Midas/GTS to simulate the force of pile foundation in frozen soil is proved.
【學(xué)位授予單位】：蘭州交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TU473.1

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