【摘要】：混凝土擴(kuò)盤樁是由普通混凝土灌注樁衍生而來,在普通混凝土灌注樁樁身增加一個(gè)或多個(gè)承力擴(kuò)大盤,根據(jù)地質(zhì)情況選擇適合的土層設(shè)置承力擴(kuò)大盤來提高樁的抗壓或抗拔承載力,實(shí)踐表明它具有承載力高、沉降變形小、施工簡便快捷等優(yōu)良特性。但是,實(shí)際工程中的地質(zhì)條件千變?nèi)f化,十分復(fù)雜,當(dāng)采用混凝土擴(kuò)盤樁時(shí),各盤就可能設(shè)置在不同土層中,目前對(duì)擴(kuò)盤樁的理論研究大多是將承力盤置于粘性土中,而關(guān)于砂土土層性狀對(duì)其承載力影響的研究相對(duì)較少。已有研究表明細(xì)粉砂土可以設(shè)置承力盤,土層的含水率、密實(shí)度對(duì)混凝土擴(kuò)盤樁的承載力產(chǎn)生很大的影響。為完善混凝土擴(kuò)盤樁在豎向壓力作用下的理論基礎(chǔ),本文在前期混凝土擴(kuò)盤樁研究成果的基礎(chǔ)上,進(jìn)一步研究細(xì)粉砂土的含水率對(duì)承力盤周圍土體破壞狀態(tài)以及擴(kuò)盤樁承載力的影響。研究方法主要采用室內(nèi)半截面樁小模型試驗(yàn)以及ANSYS有限元模擬,并對(duì)兩類分析結(jié)果進(jìn)行對(duì)比,進(jìn)一步驗(yàn)證破壞機(jī)理和承載理論的可靠性。通過試驗(yàn)的研究發(fā)現(xiàn):加載過程中盤尖端水平裂縫逐漸向樁身收斂成“心形”形狀,并最終沿裂縫發(fā)生滑移破壞,說明承力盤周圍土體破壞狀態(tài)符合滑移破壞理論,可以按此理論進(jìn)行承載力計(jì)算。同時(shí),對(duì)于含水率對(duì)研究結(jié)果的影響,試驗(yàn)研究得出,當(dāng)細(xì)粉砂土含水率在10%—17.5%范圍內(nèi)時(shí),含水率越高擴(kuò)盤樁的抗壓承載力相對(duì)越小,當(dāng)含水率高于14%左右時(shí)抗壓承載力下降較明顯。從有限元模擬分析的結(jié)果顯示:細(xì)粉砂土的含水率在10%—18%范圍內(nèi),其含水率低于14%左右時(shí)對(duì)擴(kuò)盤樁的承載力及最大位移值影響較小,其含水率高于14%左右時(shí)對(duì)擴(kuò)盤樁的承載力及最大位移值影響較大。結(jié)合試驗(yàn)過程中記錄的破壞狀態(tài)和位移-荷載曲線與有限元模擬分析的結(jié)果進(jìn)行對(duì)比,其含水率相同的情況下,二者樁周土的影響范圍以及破壞狀態(tài)基本一致,位移-荷載曲線的變化趨勢(shì)相同,至于曲線變化率的不同主要是由于室內(nèi)小模型試驗(yàn)條件的限制以及模擬分析的結(jié)果是屬于純理想狀態(tài)所致,總體來看試驗(yàn)結(jié)果與有限元模擬分析的結(jié)果是貼合的,說明分析研究的結(jié)論是可靠的。所以在工程實(shí)踐中盡量將承力盤置于含水率低于14%的細(xì)粉砂土中。本論文通過室內(nèi)小模型半面樁試驗(yàn)和有限元模擬分析兩種方法進(jìn)行研究,探討了含水率對(duì)混凝土擴(kuò)盤樁處于細(xì)粉砂土中破壞狀態(tài)及承載力的影響,彌補(bǔ)了實(shí)際工程中忽略土體含水率對(duì)擴(kuò)盤樁豎向承載力影響的欠缺,為混凝土擴(kuò)盤樁在細(xì)粉砂土土層的應(yīng)用提供理論基礎(chǔ)。
[Abstract]:The concrete expansion pile is derived from the ordinary concrete cast-in-place pile, and one or more load-bearing expanded plates are added to the ordinary concrete cast-in-place pile body. According to the geological conditions, a suitable soil layer is selected to increase the bearing capacity of the pile under compression or drawing. The practice shows that it has the advantages of high bearing capacity, small settlement and deformation, simple and quick construction, and so on. However, the geological conditions in practical engineering are varied and complex. When concrete pile is used, each plate may be placed in different soil layers. At present, most of the theoretical researches on the pile are based on putting the load plate in the clay. However, there are few studies on the effect of soil properties on the bearing capacity of sandy soil. It has been shown that the load bearing plate can be set in fine silty sand soil, the moisture content of soil layer and the compactness of soil layer have great influence on the bearing capacity of concrete pile with expanded plate. In order to improve the theoretical foundation of concrete expanded disc pile under vertical pressure, this paper is based on the previous research results of concrete expanded disc pile. The influence of the moisture content of fine silt on the failure state of soil around the bearing plate and the bearing capacity of the pile is further studied. The small model test and ANSYS finite element simulation are used to test the failure mechanism and the reliability of the bearing theory. Through the experimental study, it is found that the horizontal crack at the tip of the plate converges gradually to the "heart" shape of the pile body during loading, and finally slips along the crack, which indicates that the failure state of soil around the bearing plate accords with the theory of slip failure. The bearing capacity can be calculated according to this theory. At the same time, for the effect of moisture content on the research results, the test results show that when the moisture content of fine silty sand is in the range of 10%-17. 5%, the higher the moisture content is, the smaller the compressive capacity of the pile is. When the moisture content is higher than 14%, the compressive capacity decreases obviously. The results of finite element simulation analysis show that the moisture content of fine silty sand is in the range of 10- 18%, and when the moisture content is less than 14%, it has little effect on the bearing capacity and maximum displacement of the pile. When the moisture content is higher than 14%, the bearing capacity and the maximum displacement of the pile are greatly affected. Comparing the failure state and displacement-load curve recorded during the test with the result of finite element simulation analysis, the influence range and failure state of the soil around the pile are basically the same when the moisture content is the same. The variation trend of displacement-load curve is the same, and the variation rate of the curve is mainly due to the limitation of indoor small model test conditions and the result of simulation analysis is due to the pure ideal state. As a whole, the experimental results are consistent with the results of finite element simulation analysis, which shows that the conclusion of the analysis is reliable. Therefore, in engineering practice, the bearing plate is placed in fine silt with moisture content less than 14%. In this paper, the influence of moisture content on the failure state and bearing capacity of concrete pile in fine silt soil is studied by two methods: small model semi-plane pile test and finite element simulation analysis, and the influence of moisture content on the failure state and bearing capacity of concrete expanded sheet pile in fine silt is discussed. It makes up for the deficiency of neglecting the influence of soil moisture content on the vertical bearing capacity of the pile, and provides a theoretical basis for the application of concrete pile in fine silt soil.
【學(xué)位授予單位】：吉林建筑大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TU473.1

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