發(fā)布時間：2019-05-13 15:20

【摘要】：全夯式擠擴多頭灌注樁是通過改進(jìn)灌注樁制作工藝和施工設(shè)備,憑借在樁身不同部位設(shè)置“球型”擴大頭,不僅可以提高承載力,同時還能克服沉管灌注樁普遍存在的縮頸、斷樁、蜂窩及鋼筋籠變形扭曲等問題的一種夯擴型樁。雖然全夯式擠擴多頭灌注樁已經(jīng)在許多工程中得到應(yīng)用,但針對其承載機理、承載力計算、沉降特性等理論的研究仍是空白。本論文借助現(xiàn)場試驗、室內(nèi)模型試驗、數(shù)值模擬和理論分析等多種方法對全夯式擠擴多頭灌注樁的單樁承載機理、單樁沉降規(guī)律進(jìn)行探索,研究擴大頭在單樁沉降過程中發(fā)揮作用的規(guī)律,為全夯式擠擴多頭灌注樁的單樁沉降設(shè)計提供依據(jù),并以理論推導(dǎo)方式試著給出了該樁型的單樁沉降理論計算方法。論文研究主要獲得了以下結(jié)論:1)在樁長和樁徑相同的情況下,全夯式擠擴多頭灌注樁的極限承載力與直樁相比有明顯提高,且為2倍以上,與此相應(yīng),在同一樁頂荷載下沉降不足直孔樁的1/2。2)全夯式擠擴多頭灌注樁因在樁身不同部分處存在擴大頭,所以在其P~S曲線中存在明顯的“臺階式”跳躍。通過改變不同擴大頭間距可以調(diào)整相鄰“臺階式”跳躍的出現(xiàn)間隔。樁身擴大頭產(chǎn)生的“臺階式”跳躍幅度要大于樁端擴大頭產(chǎn)生的跳躍幅度。3)增加全夯式擠擴多頭灌注樁的擴大頭數(shù)量能夠有效增大其承載能力、減小樁頂沉降值。在本文試驗條件中,同一樁頂荷載下,擴大頭的數(shù)量越多,沉降值越小。當(dāng)樁頂施加荷載作用達(dá)到4000N時,普通直樁的沉降量是多擴大頭樁的4倍,單擴大頭樁的沉降量是多擴大頭樁的2倍。4)由于樁身擴大頭的存在,樁側(cè)摩阻力的分布特性和作用范圍發(fā)生了改變。位于擴大頭中下部的土體受到的擴大頭的應(yīng)力作用要明顯大于樁側(cè)摩阻力產(chǎn)生的應(yīng)力值。擴大頭對周邊土體的作用規(guī)模大約是樁身直徑的4倍。5)全夯式擠擴多頭灌注樁的擴大頭直徑、樁身直徑、相鄰兩個擴大頭之間的距離、樁土剛度比、細(xì)長比等都能影響樁的沉降值。因而,進(jìn)行樁基設(shè)計時,在滿足承載力要求的條件下,可以根據(jù)工程場地地層條件選擇合適的參數(shù)以減小單樁沉降值。6)基于Mindlin解和Geddes解,結(jié)合分層總和法,對全夯式擠擴多頭灌注樁的單樁沉降進(jìn)行探討。通過室內(nèi)模型試驗和理論計算值對比表明,用本文給出的計算方法得出的計算值與試驗實測值的誤差在合理范圍內(nèi),可以為將來設(shè)計工作提供參考。
[Abstract]:The full compaction extrusion multi-head cast-in-place pile is by improving the making technology and construction equipment of the cast-in-place pile. By setting up the "spherical" enlarged head in different parts of the pile body, it can not only improve the bearing capacity, but also overcome the common neck shrinkage of the sinking pipe cast-in-place pile. A rammed pile with deformation and distortion of broken pile, honeycomb and steel cage. Although the full compaction multi-head cast-in-place pile has been applied in many projects, the theoretical research on its bearing mechanism, bearing capacity calculation and settlement characteristics is still blank. In this paper, the bearing mechanism and settlement law of single pile of fully rammed extruded multi-head cast-in-place pile are explored by means of field test, indoor model test, numerical simulation and theoretical analysis. The law that the expansion head plays an important role in the settlement process of a single pile is studied, which provides the basis for the settlement design of the full compaction multi-head cast-in-place pile, and the theoretical calculation method of the settlement of the pile type is tried by means of theoretical derivation. The main conclusions of this paper are as follows: 1) under the condition that the length and diameter of the pile are the same, the ultimate bearing capacity of the fully rammed extruded multi-head cast-in-place pile is obviously higher than that of the straight pile, and it is more than twice as much as that of the straight pile. Under the same pile top load, there is an obvious "step" jump in the P 鈮，

本文編號：2475997