承臺對群樁水平承載力影響的數(shù)值分析
發(fā)布時(shí)間：2018-11-27 19:23
【摘要】：樁基礎(chǔ)是一種重要的基礎(chǔ)形式,因其造價(jià)低、承載能力高、承載力發(fā)揮穩(wěn)定等優(yōu)點(diǎn)在工程中得到了廣泛的應(yīng)用。對于樁基礎(chǔ)在水平荷載作用下的受力機(jī)理及變形特性研究一直是研究的熱點(diǎn)和難點(diǎn)。吸收塔基礎(chǔ)中常常將大塊式基礎(chǔ)作為承臺,在其下設(shè)置群樁基礎(chǔ)。現(xiàn)有的設(shè)計(jì)中,群樁的水平承載力計(jì)算只是單樁水平承載力的簡單疊加,沒有考慮群樁效應(yīng),也沒有考慮大體積承臺受到的水平抗力以及對群樁水平承載力的提高作用,因此現(xiàn)有設(shè)計(jì)方法不能反應(yīng)吸收塔基礎(chǔ)真實(shí)的水平承載力,低估了抵抗水平荷載的能力,造成了浪費(fèi)。本文利用PLAXIS 3D有限元軟件對大體積承臺群樁基礎(chǔ)在水平荷載作用下的受力和變形特性進(jìn)行了模擬計(jì)算,結(jié)合理論和設(shè)計(jì)實(shí)踐,以及室內(nèi)模型試驗(yàn),深入探究承臺對群樁水平承載力的影響。主要工作和成果如下:(1)通過對某實(shí)際工程現(xiàn)場樁基水平載荷試驗(yàn)進(jìn)行數(shù)值模擬,將數(shù)值計(jì)算結(jié)果與原始數(shù)據(jù)進(jìn)行對比,驗(yàn)證PLAXIS 3D對樁進(jìn)行水平荷載計(jì)算的可靠性;(2)建立單樁模型,分析承臺側(cè)面8體的抗力以及側(cè)面和底面的摩擦力對于單樁水平承載力的影響,承臺邊長為2 m、3 m、4 m、5 m時(shí)單樁水平承載力分別提高了 46.9%、105.9%、170.4%、207.1%。(3)建立群樁模型,對比分析了承臺高度、樁間距、承臺厚度對群樁水平承載力的影響,經(jīng)過計(jì)算發(fā)現(xiàn)上述情況下,群樁效應(yīng)綜合系數(shù)均大于1。具體來說:1)樁間距為唯一變量時(shí),群樁效應(yīng)綜合系數(shù)η隨樁間距的增加而增大,以9樁低承臺為例,樁間距由3D～6D時(shí),η值1.65-3.49。2)承臺厚度為唯一變量時(shí),隨著承臺厚度的增加,群樁效應(yīng)綜合系數(shù)η呈線性增加,以9樁低承臺群樁為例,承臺厚度0.5 m～2.0 m時(shí),對應(yīng)的η值分別為1.31-1.67。(4)選取9樁低承臺群樁基礎(chǔ)模型進(jìn)行受力分析,根據(jù)承臺前端土體的水平抗力和水平位移可以得到得到地基土水平抗力系數(shù)K(x)的分布形式,K(x)=K0+mx_,地表處水平抗力系數(shù)K0不為零,與m法相比該公式對K(x)值的計(jì)算與實(shí)際情況更為接近。(5)將群樁效應(yīng)綜合系數(shù)η的數(shù)值計(jì)算結(jié)果與規(guī)范中的計(jì)算值以及模型試驗(yàn)中的值進(jìn)行比較,由于沒有考慮豎向荷載,數(shù)值計(jì)算值比理論值小;而模型試驗(yàn)由于受模型邊界條件、加載方式等影響,η值比數(shù)值計(jì)算值小。
[Abstract]:Pile foundation is an important foundation form, which has been widely used in engineering because of its low cost, high bearing capacity and stable bearing capacity. It is a hot and difficult point to study the stress mechanism and deformation characteristics of pile foundation under horizontal load. In the absorption tower foundation, the large pile foundation is often used as the cap, and the pile group foundation is set under it. In the present design, the calculation of the horizontal bearing capacity of pile group is only a simple superposition of the horizontal bearing capacity of a single pile, without considering the effect of pile group, the horizontal resistance of large pile cap and the effect of improving the horizontal bearing capacity of pile group. Therefore, the existing design methods can not reflect the true horizontal bearing capacity of the absorption tower foundation, underestimate the ability of resisting horizontal load, and cause waste. In this paper, PLAXIS 3D finite element software is used to simulate and calculate the stress and deformation characteristics of pile group foundation under horizontal load, combined with theory and design practice, as well as indoor model test. The influence of pile cap on the horizontal bearing capacity of pile group is studied. The main work and results are as follows: (1) through the numerical simulation of the pile foundation horizontal load test in a practical project, the numerical results are compared with the original data to verify the reliability of the PLAXIS 3D horizontal load calculation of the pile; (2) the model of single pile is established, and the resistance of 8 bodies on the side of the cap and the effect of friction between the side and the bottom of the pile on the horizontal bearing capacity of the pile are analyzed. The side length of the cap is 2 m ~ 3 m ~ 4 m. At 5 m, the horizontal bearing capacity of single pile is increased by 46.9% and 105.9%, respectively. (3) the pile group model is established, and the influence of pile cap height, pile spacing and pile cap thickness on the horizontal bearing capacity of pile group is compared and analyzed. It is found by calculation that the comprehensive coefficients of pile group effect are all greater than 1. Specifically, 1) when the pile spacing is the only variable, the comprehensive coefficient 畏 of pile group effect increases with the increase of pile spacing. Taking 9 piles with low pile cap as an example, when the pile spacing is 3D~6D, 畏 value 1.65-3.49.2) when the cap thickness is the only variable, the comprehensive coefficient 畏 of pile group effect increases linearly with the increase of cap thickness. Taking 9 piles with low cap as an example, the cap thickness is 0.5 m or 2.0 m. The corresponding 畏 values are 1.31-1.67 respectively. (4) 9 pile cap pile group foundation models are selected for force analysis. According to the horizontal resistance and horizontal displacement of the soil at the front end of the cap, the distribution form of the horizontal resistance coefficient K (x) of the foundation soil can be obtained, K (x) = K0 mx_, the horizontal resistance coefficient K0 is not zero. Compared with m method, the calculation of K (x) value by this formula is closer to the actual situation. (5) the numerical calculation results of the comprehensive coefficient 畏 of pile group effect are compared with the calculated values in the code and the values in the model test. Because the vertical load is not considered, the numerical value is smaller than the theoretical value. However, the 畏 value of the model test is smaller than that of the numerical calculation because of the influence of the boundary condition and loading mode of the model.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TU473.1
本文編號：2361797
[Abstract]:Pile foundation is an important foundation form, which has been widely used in engineering because of its low cost, high bearing capacity and stable bearing capacity. It is a hot and difficult point to study the stress mechanism and deformation characteristics of pile foundation under horizontal load. In the absorption tower foundation, the large pile foundation is often used as the cap, and the pile group foundation is set under it. In the present design, the calculation of the horizontal bearing capacity of pile group is only a simple superposition of the horizontal bearing capacity of a single pile, without considering the effect of pile group, the horizontal resistance of large pile cap and the effect of improving the horizontal bearing capacity of pile group. Therefore, the existing design methods can not reflect the true horizontal bearing capacity of the absorption tower foundation, underestimate the ability of resisting horizontal load, and cause waste. In this paper, PLAXIS 3D finite element software is used to simulate and calculate the stress and deformation characteristics of pile group foundation under horizontal load, combined with theory and design practice, as well as indoor model test. The influence of pile cap on the horizontal bearing capacity of pile group is studied. The main work and results are as follows: (1) through the numerical simulation of the pile foundation horizontal load test in a practical project, the numerical results are compared with the original data to verify the reliability of the PLAXIS 3D horizontal load calculation of the pile; (2) the model of single pile is established, and the resistance of 8 bodies on the side of the cap and the effect of friction between the side and the bottom of the pile on the horizontal bearing capacity of the pile are analyzed. The side length of the cap is 2 m ~ 3 m ~ 4 m. At 5 m, the horizontal bearing capacity of single pile is increased by 46.9% and 105.9%, respectively. (3) the pile group model is established, and the influence of pile cap height, pile spacing and pile cap thickness on the horizontal bearing capacity of pile group is compared and analyzed. It is found by calculation that the comprehensive coefficients of pile group effect are all greater than 1. Specifically, 1) when the pile spacing is the only variable, the comprehensive coefficient 畏 of pile group effect increases with the increase of pile spacing. Taking 9 piles with low pile cap as an example, when the pile spacing is 3D~6D, 畏 value 1.65-3.49.2) when the cap thickness is the only variable, the comprehensive coefficient 畏 of pile group effect increases linearly with the increase of cap thickness. Taking 9 piles with low cap as an example, the cap thickness is 0.5 m or 2.0 m. The corresponding 畏 values are 1.31-1.67 respectively. (4) 9 pile cap pile group foundation models are selected for force analysis. According to the horizontal resistance and horizontal displacement of the soil at the front end of the cap, the distribution form of the horizontal resistance coefficient K (x) of the foundation soil can be obtained, K (x) = K0 mx_, the horizontal resistance coefficient K0 is not zero. Compared with m method, the calculation of K (x) value by this formula is closer to the actual situation. (5) the numerical calculation results of the comprehensive coefficient 畏 of pile group effect are compared with the calculated values in the code and the values in the model test. Because the vertical load is not considered, the numerical value is smaller than the theoretical value. However, the 畏 value of the model test is smaller than that of the numerical calculation because of the influence of the boundary condition and loading mode of the model.
【學(xué)位授予單位】：北京交通大學(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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