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地基極限承載力計(jì)算方法及安全判據(jù)研究

發(fā)布時(shí)間:2018-11-15 06:45
【摘要】:近年來(lái),我國(guó)的基礎(chǔ)建設(shè)發(fā)展迅猛,其中水利、公路、鐵路、機(jī)場(chǎng)、港口以及碼頭等基礎(chǔ)設(shè)施正在如火如荼的建設(shè)。建設(shè)這些基礎(chǔ)設(shè)施時(shí),其地基的極限承載力問(wèn)題應(yīng)該首先考慮。目前現(xiàn)有的地基極限承載力計(jì)算方法多為半經(jīng)驗(yàn)公式,且只針對(duì)均質(zhì)土地基。在工程中的地基多為復(fù)雜的層狀土地基,現(xiàn)有的層狀土地基極限承載力的計(jì)算方法尚未形成完善的理論體系。本文首先針對(duì)目前層狀土地基極限承載力計(jì)算缺乏準(zhǔn)確的計(jì)算方法的問(wèn)題,應(yīng)用上限解法,建立基于一般滑裂面的層狀土地基極限承載力的數(shù)值模擬方法;引入單純形法并結(jié)合隨機(jī)搜索法確定臨界滑動(dòng)模式及最小加載系數(shù),求解極限承載力;并基于Excel內(nèi)嵌的VBA語(yǔ)言編寫(xiě)地基極限承載力的計(jì)算程序以實(shí)現(xiàn)較為復(fù)雜函數(shù)的計(jì)算和計(jì)算的自動(dòng)化;通過(guò)與現(xiàn)場(chǎng)試驗(yàn)的對(duì)比分析證明了本方法及程序的準(zhǔn)確性。計(jì)算結(jié)果與試驗(yàn)結(jié)果表明:對(duì)于均質(zhì)土情況,,Vesic方法與本文方法的計(jì)算誤差最小,誤差不足1%, 而Meyerhof以及Terzaghi的方法與上限解的誤差最大,均超過(guò)20%;對(duì)于層狀土情況,本文方法與實(shí)驗(yàn)結(jié)果接近,邁耶霍夫漢納理論和擴(kuò)散角法的計(jì)算結(jié)果與上限解法的計(jì)算結(jié)果基本吻合,但擴(kuò)散角法的計(jì)算結(jié)果更為接近上限解法的計(jì)算結(jié)果。而利用漢森加權(quán)平均公式得出的計(jì)算結(jié)果與上限解比較相差較大。本文還探討了應(yīng)用強(qiáng)度安全系數(shù)法對(duì)地基進(jìn)行穩(wěn)定分析時(shí),安全系數(shù)的取值標(biāo)準(zhǔn)。通過(guò)工程結(jié)構(gòu)風(fēng)險(xiǎn)分析和可靠度設(shè)計(jì)方法對(duì)上述問(wèn)題進(jìn)行解答,計(jì)算結(jié)果表明其允許安全系數(shù)(1.35)應(yīng)略大于邊坡等同類建筑物的相應(yīng)值。作者將可靠度理論應(yīng)用于目標(biāo)可靠度指標(biāo)為3.7和允許安全系數(shù)為1.35的一個(gè)典型地基算例,在土的凝聚力和摩擦系數(shù)變異系數(shù)分別為0.2和0.1的條件下,獲得土的凝聚力、摩擦系數(shù)的分項(xiàng)系數(shù)的值標(biāo)定值分別為c=1.041, γf=1.418,與國(guó)外規(guī)范相近。應(yīng)用陳祖煜等提出的相對(duì)安全率判據(jù),可以發(fā)現(xiàn)上述的分項(xiàng)系數(shù)標(biāo)定值通過(guò)了普適性考核。
[Abstract]:In recent years, the infrastructure of our country is developing rapidly, such as water conservancy, highway, railway, airport, port and wharf. When building these infrastructures, the ultimate bearing capacity of the foundation should be considered first. At present, most of the existing ultimate bearing capacity calculation methods are semi-empirical formula, and only for homogeneous soil foundation. Most of the foundations in engineering are complex layered soil foundations, and the existing calculation methods of ultimate bearing capacity of layered soil foundations have not yet formed a perfect theoretical system. In this paper, aiming at the lack of accurate calculation method for the ultimate bearing capacity of layered soil foundation at present, a numerical simulation method of ultimate bearing capacity of layered soil foundation based on general sliding surface is established by using the upper limit solution. The simplex method and random search method are introduced to determine the critical sliding mode and the minimum loading coefficient to solve the ultimate bearing capacity. The calculation program of the ultimate bearing capacity of foundation is compiled based on the VBA language embedded in Excel to realize the calculation and automation of the complex function, and the accuracy of the method and program is proved by comparing with the field test. The results of calculation and experiment show that for homogeneous soil, the calculation error between Vesic method and this method is the smallest, and the error is less than 1, while the error between Meyerhof and Terzaghi method and upper bound solution is the biggest, both exceeding 20 parts. In the case of layered soil, the present method is close to the experimental results. The results of Meyerhoff Hanna theory and diffusion angle method are in good agreement with those of the upper bound method, but the results of diffusion angle method are closer to those of the upper bound method. However, the calculation results obtained by using Hansen's weighted average formula are quite different from the upper bound solutions. This paper also discusses the criterion of safety factor when using the method of strength safety factor to analyze the stability of foundation. By means of engineering structural risk analysis and reliability design method, the results show that the allowable safety factor (1.35) should be slightly larger than the corresponding value of similar buildings such as slope. The reliability theory is applied to a typical foundation with a target reliability index of 3.7 and a allowable safety factor of 1.35. The coefficient of variation of cohesion and friction coefficient is 0.2 and 0.1, respectively. The values of cohesion and friction coefficient of soil are determined to be c _ (1.041) and 緯 _ f _ (1.418) respectively, which are close to those of foreign specifications. By applying the criterion of relative safety rate proposed by Chen Zuyu et al, it can be found that the calibration values of the above sub-coefficients have passed the universal assessment.
【學(xué)位授予單位】:西安理工大學(xué)
【學(xué)位級(jí)別】:碩士
【學(xué)位授予年份】:2017
【分類號(hào)】:TU470

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