本文選題：剛性樁復合地基　切入點：數(shù)值模擬　出處：《浙江大學》2014年碩士論文　論文類型：學位論文

【摘要】：剛性樁復合地基技術(shù)因具有施工方便、承載力高、穩(wěn)定性好等優(yōu)點而被廣泛應用于軟弱土地區(qū)的工程實踐中,但整體失穩(wěn)事故時有發(fā)生。研究其失穩(wěn)破壞機理以防止類似事故的發(fā)生,是工程界亟待解決的問題。 本文主要研究內(nèi)容如下： (1)結(jié)合已有離心機試驗模型,采用大型通用有限元軟件ABAQUS建立考慮樁-土接觸的剛性樁復合地基支承路堤的三維有限元分析模型。將有限元模擬結(jié)果與離心機試驗及已有研究成果進行了對比,驗證了本文有限元模型的合理性與可行性。 (2)對剛性樁復合地基的失穩(wěn)臨界點進行討論,發(fā)現(xiàn)特征點位移-加載曲線變化情況與土體塑性區(qū)發(fā)展變化的規(guī)律較為一致,將特征點位移突變結(jié)合塑性區(qū)貫通作為失穩(wěn)判據(jù)較合理。 (3)分析了樁身抗彎剛度、樁端嵌固條件、樁間距對路堤下剛性樁復合地基樁土受力變形的影響,并選取典型算例分析了上述不同條件下的失穩(wěn)破壞規(guī)律,研究表明：在一定范圍內(nèi)增大樁抗彎剛度能有效提高復合地基的穩(wěn)定性,但樁身剛度過大時易發(fā)生樁間土繞流破壞；樁端嵌入持力層的深度為樁徑的3～6.25倍時增加樁長能有效提高復合地基的穩(wěn)定性,過大的嵌固深度會造成不必要的浪費,而樁端未打穿軟土層或嵌固深度不足時樁體易發(fā)生傾覆破壞,不能充分發(fā)揮樁的強度；樁間距為樁徑的2.5～7.5倍時減小樁間距能有效提高復合地基的穩(wěn)定性,樁間距的增大會影響樁體的破壞模式,樁體在第一次彎曲破壞面以上可能發(fā)生二次彎曲破壞,樁間距過小則樁間土不能充分發(fā)揮其強度。 (4)建立了樁承加筋土復合地基支承路堤的三維有限元模型,分析了鋪設土工格柵后復合地基的失穩(wěn)破壞規(guī)律,并研究了格柵剛度、墊層厚度、加筋位置等因素對樁承加筋土復合地基穩(wěn)定的影響,研究表明：土工格柵調(diào)節(jié)了樁土應力,減小了土體塑性區(qū)范圍和深度,影響了滑動區(qū)的形狀,顯著提高了復合地基的穩(wěn)定性,但鋪設土工格柵后復合地基的失穩(wěn)破壞模式與未加筋的情況相似;格柵剛度處于2000-4000kN/m、墊層厚度為0.4m～0.6m、土工格柵位于樁頂時復合地基的穩(wěn)定性最好。
[Abstract]:The technology of rigid pile composite foundation is widely used in engineering practice in soft soil area because of its advantages of convenient construction, high bearing capacity and good stability. However, the overall instability accidents occur from time to time. It is an urgent problem to study the failure mechanism to prevent the occurrence of similar accidents. The main contents of this paper are as follows:. 1) combined with the existing centrifuge test model, A three-dimensional finite element analysis model of embankment supported on rigid pile composite foundation considering pile-soil contact was established by using ABAQUS, the finite element simulation results were compared with the results of centrifuge test and existing research. The rationality and feasibility of the finite element model are verified. 2) the critical point of instability of rigid pile composite foundation is discussed. It is found that the change of displacement-loading curve of characteristic point is consistent with that of soil plastic zone. It is reasonable to take the abrupt displacement of the characteristic point and the transfixion of the plastic zone as the criterion of instability. This paper analyzes the influence of bending stiffness of pile body, the condition of pile end embedding and the spacing of pile on the stress and deformation of pile and soil in rigid pile composite foundation under embankment, and selects a typical example to analyze the law of instability and failure under the above different conditions. The results show that the stability of composite foundation can be effectively improved by increasing the flexural stiffness of piles in a certain range, but the soil flow around piles is easy to occur when the pile body is over large. When the depth of the bearing layer embedded at the end of the pile is 3 ~ 6.25 times of the diameter of the pile, increasing the length of the pile can effectively improve the stability of the composite foundation, and if the depth of the embedded layer is too large, it will cause unnecessary waste. However, when the pile ends do not penetrate the soft soil layer or the embedded depth is insufficient, the pile body is prone to overturn and destroy, and the pile strength can not be brought into full play, and the stability of the composite foundation can be effectively improved by decreasing the pile spacing when the pile spacing is 2.5 or 7.5 times the diameter of the pile. The increase of pile spacing will affect the failure mode of pile body. Second bending failure of pile body may occur above the first bending failure surface, but if the pile spacing is too small, the strength of soil between piles can not be fully exerted. 4) the three-dimensional finite element model of supported embankment on pile-supported reinforced soil composite foundation is established, and the instability failure law of composite foundation after laying geogrid is analyzed, and the stiffness of grid and the thickness of cushion layer are studied. The influence of reinforcement position on the stability of pile-supported reinforced soil composite foundation is studied. The results show that the geogrid adjusts the stress of pile and soil, reduces the range and depth of soil plastic zone, and influences the shape of sliding zone. The stability of composite foundation is improved obviously, but the instability failure mode of composite foundation after laying geogrid is similar to that of unreinforced ground, the stiffness of grid is in 2000-4000kN / m, the thickness of cushion is 0.4mand 0.6m. the stability of composite foundation is the best when geogrid is located at the top of pile.
【學位授予單位】：浙江大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TU470

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