本文選題：剛性樁復(fù)合地基 + 群樁��； 參考：《華南理工大學(xué)》2013年博士論文

【摘要】：廣東粵北地區(qū)的韶關(guān)、清遠(yuǎn)、肇慶等地，作為巖溶相當(dāng)發(fā)育的地區(qū)，存在較多的工程隱患，因此，迫切要求找到合適的基礎(chǔ)形式和地基處理方式。在華南理工大學(xué)亞熱帶建筑科學(xué)國家重點實驗室重點項目的資助下，就這一問題，華南理工大學(xué)土木與交通學(xué)院對巖溶地區(qū)地基處理關(guān)鍵技術(shù)進(jìn)行了深入的研究，并在粵北地區(qū)進(jìn)行了一系列的試驗、測試和觀測。 采用單樁壓板試驗確定復(fù)合地基承載力，忽視了群樁對復(fù)合地基受力性能的影響，無法合理確定樁土承載能力的發(fā)揮情況。在進(jìn)行考慮上下部相互作用的結(jié)構(gòu)分析時，由于計算機(jī)的限制往往難以進(jìn)行，提出符合工程實際的、便于計算分析的方法顯得尤為重要。而且，在對筏基的實測中發(fā)現(xiàn)，筏板鋼筋的應(yīng)力測量值明顯小于計算值，說明原有計算模型存在不足且偏于保守，所以要求設(shè)計方法應(yīng)能更真實地反映筏板中鋼筋的實際受力情況。同時，隨著復(fù)合地基在抗震地區(qū)的廣泛應(yīng)用，對結(jié)構(gòu)與復(fù)合地基之間動力相互作用的研究也十分迫切。本文采用理論分析與試驗研究相結(jié)合的方法，以實際工程為背景，圍繞剛性樁復(fù)合地基-筏基-上部結(jié)構(gòu)體系進(jìn)行了深入的研究，主要研究內(nèi)容及創(chuàng)新性工作有以下幾個方面： 1）進(jìn)行了24個復(fù)雜巖溶地質(zhì)條件下的單樁復(fù)合地基載荷試驗。結(jié)果表明，樁間土的承載能力發(fā)揮較早，在特征值荷載時樁土很難達(dá)到各自的設(shè)計值；無墊層，當(dāng)土層承載力較高時，只要基礎(chǔ)與墊層接觸緊密，土體仍可發(fā)揮一定的承載力；砂石墊層厚100mm，特征值荷載下的樁間土平均應(yīng)力為0.31MPa，樁-土應(yīng)力比約19，土承擔(dān)荷載比為46.5%，樁、土承載力發(fā)揮系數(shù)分別約為0.72、1.78。砂石墊層厚300mm，特征值荷載下樁間土平均應(yīng)力約為0.38Mpa，樁-土應(yīng)力比14.6，土承擔(dān)荷載比為61%。分析表明該種處理方案可行。 2）通過與單樁復(fù)合地基壓板試驗對比，驗證了所采用的土體彈塑性模型、接觸關(guān)系和所選參數(shù)的正確性，可以較為準(zhǔn)確地分析剛性樁復(fù)合地基的受力、變形性能。在此基礎(chǔ)上，，研究了群樁復(fù)合地基載荷板的尺寸效應(yīng)，得到了大尺寸壓板的最終沉降估算公式，墊層厚度為100mm，基礎(chǔ)邊長為30m、40m、50m的最終沉降為16.7mm、17.5mm、18.1mm，墊層厚度為300mm，基礎(chǔ)邊長為30m、40m、50m的最終沉降為32.4mm、34.5mm、36.1mm，與實測值吻合。分析了群樁復(fù)合地基的宏觀本構(gòu)關(guān)系，結(jié)果表明，隨著樁數(shù)的增多壓板沉降增大，土體承載能力發(fā)揮度減小。墊層厚為100mm、200mm、300mm，特征值荷載作用下，49樁復(fù)合地基的平均沉降約是單樁復(fù)合地基平均沉降的1.6、2.18、2.2倍，此時，土應(yīng)力分別為單樁復(fù)合地基土應(yīng)力的46%、65%、78%；加載初期，單、多樁的刺入相差不大，隨荷載增加群樁的刺入量比單樁大，墊層厚度為100mm、200mm、300mm，特征值荷載下單樁的刺入量分別為3.9mm、6.8mm、8.4mm，49樁的刺入量分別為6.8mm、18.7mm、19.2mm。群樁在達(dá)到49個，以及墊層達(dá)到300mm后，樁土應(yīng)力、基礎(chǔ)沉降、剛性樁的刺入等變化很少，褥墊層的調(diào)節(jié)作用趨于穩(wěn)定。 3）根據(jù)試驗和群樁有限元分析，結(jié)合工程經(jīng)驗，提出了針對該類復(fù)合地基的二折線彈簧宏觀本構(gòu)模型，特征值荷載對應(yīng)的沉降為12mm，極限荷載對應(yīng)的沉降為40mm。借助SAP2000可以利用該模型進(jìn)行考慮上部結(jié)構(gòu)與復(fù)合地基相互作用的基礎(chǔ)受力分析，特征值荷載對應(yīng)的基礎(chǔ)沉降從4mm到20mm進(jìn)行變化，除個別地方的筏板彎矩變化幅值接近9%，其它地方變化都很小。結(jié)果表明，該方法既可以考慮上部結(jié)構(gòu)剛度對基礎(chǔ)的影響，又可以反應(yīng)土體一定程度的非線性特性和基礎(chǔ)的整體沉降。 4）建立地基的實體單元模型，考慮筏板與墊層之間的摩擦，借助ABAQUS進(jìn)行考慮上部結(jié)構(gòu)與復(fù)合地基相互作用的彈塑性分析。結(jié)果表明，在彈塑性計算中荷載設(shè)計值下，截面應(yīng)力分布較均勻，截面最大拉應(yīng)力約為1.63Mpa，鋼筋最大應(yīng)力約80Mpa；荷載標(biāo)準(zhǔn)值下鋼筋最大應(yīng)力為48Mpa，計算結(jié)果與實測值吻合較好，驗證了本文分析方法的正確性。通過計算分析，與常用方法的計算結(jié)果比較表明，地基反力模式、筏板與墊層之間的摩擦是影響筏板內(nèi)力計算結(jié)果的主要因素。地基反力在筏板邊緣劇增，最大值達(dá)到平均值的3.5倍，極易造成地基局部區(qū)域的提前破壞。最后，分析了地基土變形模量、褥墊層厚度、褥墊層模量、筏板厚度等參數(shù)對筏板內(nèi)力及變形的影響。結(jié)果表明，地基反力和筏板應(yīng)力與筏板同地基相對剛度有關(guān)。 5）采用有限元與無限元耦合的方法，建立動力相互作用三維整體模型，進(jìn)行了動力彈塑性時程分析。通過與普通樁筏基礎(chǔ)的時程分析結(jié)果對比，研究了剛性樁復(fù)合地基-上部結(jié)構(gòu)體系的抗震性能。結(jié)果表明，7度小震時，復(fù)合地基沒有減震作用；7度大震時，樁基中樁體彎矩、剪力最大值是剛性樁復(fù)合地基中樁體彎矩、剪力最大值的1.8倍，褥墊層產(chǎn)生了較大的塑性變形和相對基底的滑移，具有一定的耗能減震作用，并且復(fù)合地基中筏基及上部結(jié)構(gòu)的動力響應(yīng)約是樁基體系中對應(yīng)量的90%，減震系數(shù)在0.8-0.9之間。 本論文的研究成果已應(yīng)用于廣東粵北地區(qū)的碧湖苑、時代美居、翠湖花園等工程項目建設(shè)中，取得良好效果。
[Abstract]:Shaoguan, Qingyuan, Zhaoqing and other places in the north of Guangdong Province, as a relatively developed area of karst, there are many hidden dangers of engineering. Therefore, it is urgent to find the appropriate basic forms and foundation treatment methods. Under the support of the key project of the National Key Laboratory of subtropical architecture science of South China University of Technology, South China Science and technology The Institute of civil engineering and transportation has conducted an in-depth study of key technologies for foundation treatment in karst areas, and conducted a series of tests, tests and observations in northern Guangdong.
The bearing capacity of composite foundation is determined by single pile pressure plate test, and the effect of pile group on the bearing capacity of composite foundation is ignored. It is not reasonable to determine the bearing capacity of the pile and soil. In the analysis of the interaction of the upper and lower parts, the computer restrictions are often difficult to carry out in the consideration of the interaction of the upper and lower parts. The analysis method is particularly important. Moreover, in the measurement of raft foundation, it is found that the stress measurement value of the raft steel bar is obviously less than the calculated value, which indicates that the original calculation model is insufficient and conservative. Therefore, the design method should be able to reflect the actual stress situation of the reinforcement in the raft more truthfully. At the same time, with the composite foundation in the earthquake resistant area The study of dynamic interaction between structure and composite foundation is very urgent. This paper combines theoretical analysis and experimental research, and takes practical engineering as the background to study the rigid pile composite foundation raft foundation superstructure system. The main research content and innovative work are as follows On the other hand:
1) the load test of single pile composite foundation under 24 complex karst geological conditions has been carried out. The results show that the bearing capacity of the soil between piles is early, and the pile and soil are difficult to reach their respective design values when the characteristic load is loaded; when the bearing capacity of the soil layer is high, the soil can still play a certain bearing capacity as long as the foundation is closely contacted with the cushion. The gravel cushion is 100mm, the average stress of the soil under the characteristic load is 0.31MPa, the pile to soil stress ratio is about 19, the soil bearing load ratio is 46.5%, the bearing capacity of pile and soil is about 300mm, the average stress of the soil under the characteristic load is about 0.38Mpa, the pile soil stress ratio is 14.6, the soil bearing load ratio is 61%. analysis. It shows that the treatment scheme is feasible.
2) by comparing with the single pile composite foundation pressure plate test, the elastoplastic model of soil, the contact relationship and the correctness of the selected parameters are verified, and the stress and deformation performance of the rigid pile composite foundation can be more accurately analyzed. On this basis, the size effect of the composite foundation load plate is studied, and the large size pressure plate is obtained. The final settlement estimation formula, the thickness of the cushion is 100mm, the base length is 30m, the final settlement of the 40m, 50m is 16.7mm, 17.5mm, 18.1mm, the thickness of the cushion is 300mm, the base length is 30m, the 40m, 50m is finally settled by the 32.4mm, it is consistent with the measured value. The macroscopic constitutive relation of the pile composite foundation is analyzed, the result shows that with the increase of pile number, the number of piles is increased. Under the action of 100mm, 200mm, 300mm, the average settlement of the 49 pile composite foundation is about 1.6,2.18,2.2 times of the average settlement of the single pile composite foundation, and the soil stress is 46%, 65%, 78% of the soil stress of the single pile composite foundation, respectively. The prickling amount of the pile group is larger than that of single pile with the increase of load. The thickness of the cushion is 100mm, 200mm, 300mm. The prickling amount of single pile under the characteristic load is 3.9mm, 6.8mm, 8.4mm, the 49 piles are respectively 6.8mm, 18.7mm, 19.2mm. group pile in 49, and after the cushion reaches 300mm, the pile soil stress, foundation settlement, rigid pile stab entry and so on Rarely, the adjustment of the mattress layer tends to be stable.
3) according to the test and the group pile finite element analysis, combined with the engineering experience, a macroscopic constitutive model of two fold spring for this kind of composite foundation is proposed. The corresponding settlement of the eigenvalue load is 12mm. The settlement of the corresponding limit load is 40mm. with the aid of SAP2000, the model can be used to consider the foundation of the interaction between the superstructure and the composite foundation. According to the force analysis, the foundation settlement corresponding to the eigenvalue load changes from 4mm to 20mm. The amplitude of the raft bending moment change in some places is close to 9%, and the changes in other places are very small. The results show that the method can not only consider the influence of the superstructure stiffness on the foundation, but also reflect the nonlinear characteristics of the soil body and the whole subsidence of the foundation. Drop.
4) establishing the solid element model of the foundation, considering the friction between the raft and the cushion, and considering the elastoplastic analysis of the interaction between the superstructure and the composite foundation with the help of ABAQUS. The results show that under the load design value, the stress distribution of the section is more uniform, the maximum tensile stress of the section is about 1.63Mpa, and the maximum stress of the steel bar is about 80Mpa The maximum stress of the steel bar under the load standard is 48Mpa, and the calculation results are in good agreement with the measured values. The correctness of the analysis method is verified. The calculation analysis shows that the friction between the foundation and the cushion is the main factor affecting the calculation results of the internal force of the raft. On the edge of the raft, the maximum value reached 3.5 times the average value, which could easily cause early damage to the local area of the foundation. Finally, the influence of the deformation modulus of the foundation soil, the thickness of the cushion, the cushion modulus and the thickness of the raft plate on the internal force and deformation of the raft was analyzed. The results showed that the relative stiffness of the foundation and raft plate was relative to the raft foundation. Of
5) the dynamic elastoplastic time history analysis is carried out by using the coupling method of finite element and infinite element, and the dynamic elastoplastic time history analysis is carried out. By comparing with the time history analysis of ordinary pile raft foundation, the seismic performance of the rigid pile composite foundation superstructure system is studied. The results show that the composite foundation has no shock absorption when the 7 degree small earthquake. When the 7 degree earthquake, the bending moment of the pile in the pile foundation is the maximum value of the pile bending moment in the rigid pile composite foundation and the maximum value of the shear force of 1.8 times. The cushion layer produces a large plastic deformation and relative base slip, which has a certain energy dissipation and damping effect, and the dynamic response of the raft foundation and the superstructure in the composite foundation is about the pile foundation system. 90% of the corresponding amount, the damping coefficient is between 0.8-0.9.
The research results of this paper have been applied to the construction of the Bi Hu Yuan in the north of Guangdong, the beauty of the times, and the construction of the green lake garden.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：TU472

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