【摘要】：受環(huán)向拱效應(yīng)的影響,圓形基坑的主動(dòng)土壓力小于直邊基坑的主動(dòng)土壓力。但在實(shí)際工程設(shè)計(jì)中,由于缺乏完善的理論基礎(chǔ)及相應(yīng)的計(jì)算方法,設(shè)計(jì)人員多采用平面土壓力理論計(jì)算圓形基坑的土壓力,導(dǎo)致成本增加、資源浪費(fèi)。本文對(duì)圓形基坑彈塑性問(wèn)題的計(jì)算模型進(jìn)行改進(jìn),運(yùn)用軸對(duì)稱滑移線法和極限分析的上限解法推導(dǎo)了其主動(dòng)土壓力的計(jì)算公式,采用數(shù)值模擬方法計(jì)算分析了圓形基坑土體中主應(yīng)力系數(shù)的影響因素。具體內(nèi)容如下:(1)在圓形基坑的彈塑性空間軸對(duì)稱問(wèn)題中,環(huán)向應(yīng)力即為中間主應(yīng)力。本文引入中主應(yīng)力系數(shù)b,即假設(shè)σ2=σθ=σ3+b(σ1-σ3),改進(jìn)了目前計(jì)算中所廣泛采用的σ2=σ1或σ2=σ3的HaarKarman完全塑性假定,使其更符合工程實(shí)際情況。(2)運(yùn)用滑移線場(chǎng)理論,推導(dǎo)了空間軸對(duì)稱問(wèn)題的滑移線方程。通過(guò)將墻后土體的滑移曲線簡(jiǎn)化為直線形式,求解滑移線方程,得到圓形基坑土壓力的計(jì)算公式,并分析了土壓力的分布模式。計(jì)算結(jié)果表明,圓形基坑土壓力隨著深度的增加呈非線性分布,但在較淺的范圍內(nèi)可以認(rèn)為是線性分布形式。此外,分析了基坑半徑對(duì)土壓力的影響,結(jié)果表明土壓力隨半徑的增大而增大,最終趨于平面Rankine 土壓力。(3)采用極限分析中的上限法,同時(shí)引入中主應(yīng)力系數(shù)b,并考慮環(huán)向應(yīng)力做功引起內(nèi)能耗散,推導(dǎo)了圓形基坑土壓力合力的計(jì)算公式。計(jì)算結(jié)果表明,不同中主應(yīng)力系數(shù)b對(duì)應(yīng)的土壓力明顯小于平面情況下土壓力。當(dāng)半徑趨于很大時(shí),b所對(duì)應(yīng)的結(jié)果趨于相同,該值即為在平面情況下Rankine 土壓力值。此外,圓形基坑破壞面傾角受中主應(yīng)力系數(shù)影響很大,b值越大時(shí),土體破壞面傾角越大;b值越小時(shí),土體破壞面傾角越小;隨著圓形基坑半徑的增大,土體破壞面傾角將減小。當(dāng)開(kāi)挖半徑足夠大時(shí),破壞面傾角趨于45°+φ/2。(4)通過(guò)有限元計(jì)算,分析了圓形基坑中主應(yīng)力系數(shù)的影響因素及其變化規(guī)律。結(jié)果表明,基坑半徑及土體內(nèi)摩擦角是中主應(yīng)力系數(shù)取值的主要影響因素,而黏聚力的影響較小�；影霃郊皟�(nèi)摩擦角越小,中主應(yīng)力系數(shù)越大且趨于1.0。為便于實(shí)際工程應(yīng)用,作者通過(guò)大量計(jì)算分析,給出了圓形基坑土體中主應(yīng)力系數(shù)的建議取值。
[Abstract]:Under the influence of circumferential arch effect, the active earth pressure of circular foundation pit is smaller than that of straight side foundation pit. However, in the practical engineering design, due to the lack of perfect theoretical basis and the corresponding calculation method, the designers often use the plane earth pressure theory to calculate the earth pressure of circular foundation pit, which leads to the increase of cost and the waste of resources. In this paper, the calculation model of elastic-plastic problem of circular foundation pit is improved, and the calculation formula of active earth pressure is derived by using axisymmetric slip line method and upper limit method of limit analysis. The influence factors of principal stress coefficient in circular foundation pit soil are calculated and analyzed by numerical simulation method. The main contents are as follows: (1) in the elastic-plastic space axisymmetric problem of circular foundation pit, the toroidal stress is the intermediate principal stress. In this paper, the intermediate principal stress coefficient b, which is assumed to be 蟽 2 = 蟽 胃 = 蟽 3 b (蟽 1- 蟽 3), is introduced to improve the HaarKarman complete plasticity assumption of 蟽 2 = 蟽 1 or 蟽 2 = 蟽 3, which is widely used in the calculation, so that it is more suitable for engineering practice. (2) the slip line field theory is used. The slip line equation of space axisymmetric problem is derived. By simplifying the slip curve of the soil behind the wall into a straight line form and solving the slip line equation, the calculation formula of the earth pressure of the circular foundation pit is obtained, and the distribution model of the earth pressure is analyzed. The results show that the earth pressure of circular foundation pit is nonlinear distribution with the increase of depth, but it can be regarded as a linear distribution form in a shallow range. In addition, the influence of foundation pit radius on earth pressure is analyzed. The results show that the earth pressure increases with the increase of radius and eventually tends to plane Rankine earth pressure. (3) the upper limit method of limit analysis is used. At the same time, the calculation formula of the earth pressure force of circular foundation pit is derived by introducing the coefficient of intermediate principal stress b and considering the internal energy dissipation caused by the work of circumferential stress. The calculated results show that the earth pressure corresponding to different principal stress coefficients b is obviously smaller than that under plane condition. When the radius tends to be very large, the corresponding result of b tends to be the same, that is, the value of Rankine earth pressure in plane case. In addition, when the slope of the failure surface of circular foundation pit is greatly affected by the principal stress coefficient, the larger the slope angle of soil failure surface is, the smaller the slope angle of soil failure surface is, and the smaller the slope angle of soil failure surface is with the increase of radius of circular foundation pit. When the excavation radius is large enough, the slope of the failure surface tends to be 45 擄蠁 / 2. (4) through finite element calculation, the influencing factors of principal stress coefficient and its variation law in circular foundation pit are analyzed. The results show that the radius of foundation pit and the internal friction angle of soil are the main factors affecting the value of the coefficient of principal stress, but the influence of cohesion is small. The smaller the radius of foundation pit and the angle of internal friction, the larger the coefficient of principal stress is and tends to 1.0. In order to facilitate practical engineering application, the author gives the suggested value of principal stress coefficient in the soil of circular foundation pit through a lot of calculation and analysis.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TU432

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