【摘要】：隨著我國(guó)高速鐵路和重載鐵路的發(fā)展,客運(yùn)列車既有線提速及貨運(yùn)列車軸重的提升都會(huì)引起橋墩基礎(chǔ)承載力安全儲(chǔ)備的降低。目前我國(guó)采用的橋梁檢測(cè)的相關(guān)方法和規(guī)程主要針對(duì)橋梁上部結(jié)構(gòu)和橫向振動(dòng),對(duì)于橋墩基礎(chǔ)豎向承載力的無損檢測(cè)評(píng)估方法尚不完善。以群樁-承臺(tái)基礎(chǔ)為例,傳統(tǒng)的靜載試驗(yàn)和高應(yīng)變測(cè)樁法均無法滿足對(duì)既有橋墩基礎(chǔ)承載性能快速普查的無損檢測(cè)需求。因此,發(fā)展一套用于評(píng)價(jià)橋墩基礎(chǔ)豎向承載能力的動(dòng)力無損檢測(cè)方法就顯得尤為重要。目前,用于橋樁豎向承載力評(píng)價(jià)的動(dòng)力無損檢測(cè)方法主要有兩類,除高應(yīng)變測(cè)樁法外,另一種是以機(jī)械阻抗法為測(cè)試手段發(fā)展而來的動(dòng)剛度綜合評(píng)價(jià)法。當(dāng)橋樁承載力由變形控制時(shí),動(dòng)剛度與靜剛度之間通過動(dòng)靜對(duì)比系數(shù)加以換算。既有實(shí)驗(yàn)研究表明,采用動(dòng)剛度作為評(píng)價(jià)指標(biāo)時(shí),動(dòng)剛度與樁基豎向承載力之間存在正相關(guān)關(guān)系。然而,以往研究對(duì)象多以單樁為主,并沒有考慮承臺(tái)和橋墩對(duì)動(dòng)剛度的影響。對(duì)于廣泛使用的群樁-橋墩結(jié)構(gòu)系統(tǒng),采用動(dòng)剛度指標(biāo)評(píng)價(jià)是否仍具有可靠性,尚缺乏系統(tǒng)的研究�；诖�,本文通過室內(nèi)原理性試驗(yàn)和數(shù)值模擬,對(duì)群樁-承臺(tái)-橋墩系統(tǒng)豎向動(dòng)剛度的影響因素及其特征進(jìn)行了系統(tǒng)的研究分析,主要工作如下:(1)基于瞬態(tài)機(jī)械阻抗法的基本原理,建立了群樁-承臺(tái)-橋墩的原理性試驗(yàn)?zāi)Ｐ�。采用木材和石膏兩種材料分別對(duì)樁基缺陷、樁徑、樁周有效摩擦面積和墩身高度對(duì)群樁-承臺(tái)-橋墩系統(tǒng)豎向動(dòng)剛度的影響以及單樁與群樁-承臺(tái)系統(tǒng)豎向動(dòng)剛度之間的關(guān)系進(jìn)行了測(cè)試研究;(2)結(jié)合現(xiàn)場(chǎng)模型樁的動(dòng)靜檢測(cè)數(shù)據(jù),驗(yàn)證了所建立的樁-土三維有限元分析模型參數(shù)的合理性,并從材料因素(混凝土彈模、泊松比,土體的彈模和土層變化等)和幾何因素(單樁、單樁-承臺(tái)和群樁-承臺(tái),樁長(zhǎng),墩身以及樁體幾何缺陷等)兩個(gè)角度對(duì)群樁-承臺(tái)-橋墩系統(tǒng)豎向動(dòng)剛度的影響及其特征進(jìn)行了研究。本文由以上工作得到結(jié)論如下:(1)與完整樁相比,擴(kuò)徑樁豎向動(dòng)剛度值明顯偏大,而縮徑樁和短樁(樁基實(shí)際長(zhǎng)度不滿足設(shè)計(jì)要求)則與擴(kuò)徑樁情況相反;缺陷樁的缺陷部位越接近承臺(tái)底面,對(duì)群樁-承臺(tái)系統(tǒng)豎向動(dòng)剛度值影響越大;樁基豎向動(dòng)剛度與樁徑成正相關(guān);群樁-承臺(tái)結(jié)構(gòu)系統(tǒng)豎向動(dòng)剛度隨著樁周有效摩擦面積的減小而減小;隨著墩身的增高,群樁-承臺(tái)-橋墩系統(tǒng)豎向動(dòng)剛度呈減小的趨勢(shì)。(2)群樁-承臺(tái)系統(tǒng)豎向動(dòng)剛度值與結(jié)構(gòu)混凝土彈性模量和泊松比成正比;隨著樁周土層動(dòng)彈性模量的增大,群樁-承臺(tái)系統(tǒng)豎向動(dòng)剛度值也隨著增大,其中摩擦樁對(duì)樁周土體的變化較端承樁敏感。隨著樁基周圍土層等厚度降低,系統(tǒng)豎向動(dòng)剛度值下降百分比逐漸減緩。(3)群樁-承臺(tái)系統(tǒng)豎向動(dòng)剛度值介于n-1倍和n倍單樁-承臺(tái)系統(tǒng)豎向動(dòng)剛度值之間(其中n為承臺(tái)下樁基的數(shù)量);摩擦樁系統(tǒng)豎向動(dòng)剛度值隨著樁長(zhǎng)的增大呈現(xiàn)增大,端承樁系統(tǒng)豎向動(dòng)剛度值隨著樁長(zhǎng)的增大呈現(xiàn)減小,在樁長(zhǎng)為20m時(shí)系統(tǒng)豎向動(dòng)剛度值趨于穩(wěn)定。
[Abstract]:With the development of high-speed railway and heavy haul railway in our country, both the speed-up of the passenger train and the lifting of the freight train will cause the reduction of the safety reserve of the pier foundation bearing capacity. At present, the related methods and regulations of bridge detection adopted by our country are mainly aimed at the superstructure and lateral vibration of the bridge, and the nondestructive detection and evaluation method for the vertical bearing capacity of the pier foundation is not perfect. On the basis of group pile-bearing platform, the traditional static load test and the high strain gauge pile method can not meet the requirement of nondestructive testing for rapid census of existing pier foundation bearing performance. Therefore, it is very important to develop a set of dynamic nondestructive testing methods for evaluating the vertical bearing capacity of pier foundation. At present, there are two kinds of dynamic nondestructive testing methods for the evaluation of vertical bearing capacity of bridge piles. In addition to the high strain gauge pile method, the other is the dynamic stiffness comprehensive evaluation method developed by the mechanical impedance method as the test means. When the bearing capacity of bridge pile is controlled by deformation, the dynamic stiffness and static stiffness are converted by dynamic and static contrast coefficient. There is a positive correlation between dynamic stiffness and vertical bearing capacity of pile foundation when dynamic stiffness is used as the evaluation index. However, the previous research objects are mainly single-pile, and do not consider the influence of bearing platform and pier on dynamic stiffness. For a widely used group pile-pier structure system, the dynamic stiffness index evaluation is used to evaluate whether it still has the reliability, and the research on the system is still lacking. Based on this, the influence factors and their characteristics of vertical dynamic stiffness of pile-bearing platform-pier system are analyzed by indoor principle test and numerical simulation. The main work is as follows: (1) The basic principle of transient mechanical impedance method is given. The principle test model of pile-bearing platform-pier was established. The relationship between pile foundation defect, pile diameter, effective friction area of pile and pier height on vertical dynamic stiffness of pile-bearing platform-pier system and the relationship between single pile and vertical dynamic stiffness of pile-bearing platform system were studied by using two kinds of materials of wood and gypsum respectively. (2) According to static and static detection data of the on-site model pile, the rationality of the parameters of the established pile-soil three-dimensional finite element analysis model is verified, and the material factors (concrete elastic modulus, shear modulus, elastic modulus of soil body and soil layer change, etc.) and geometric factors (single pile) are verified. The influence of single-pile-bearing platform and pile-bearing platform, pile length, pier body and geometric defect of pile body on vertical dynamic stiffness of pile-bearing platform-pier system are studied. The results obtained from the above work are as follows: (1) Compared with the complete pile, the vertical dynamic stiffness value of the enlarged diameter pile is obviously larger, while the diameter pile and the short pile (the actual length of the pile foundation do not meet the design requirement) are opposite to the case of the enlarged diameter pile; the closer the defect part of the defect pile is closer to the bottom surface of the bearing platform, The influence of vertical dynamic stiffness value of pile-bearing platform system is larger, the vertical dynamic stiffness of pile foundation is positively related to pile diameter, the vertical dynamic stiffness of pile-bearing platform structure decreases with the decrease of effective friction area of pile, The vertical dynamic stiffness of pile-bearing platform-pier system is decreasing. (2) The vertical dynamic stiffness value of the pile-bearing platform system is directly proportional to the elastic modulus and Poisson's ratio of the structural concrete; with the increase of the dynamic elastic modulus of the soil layer of the pile, the vertical dynamic stiffness value of the pile-bearing platform system increases with the increase, among which the friction pile is sensitive to the change of soil body at the end of the pile. As the thickness of surrounding soil layer of pile foundation decreases, the decrease percentage of vertical dynamic stiffness value of the system gradually decreases. (3) The vertical dynamic stiffness value of the pile-bearing platform system is between n-1 times and the vertical dynamic stiffness value of the n-fold single pile-bearing platform system (where n is the number of pile foundation below the bearing table); the vertical dynamic stiffness value of the friction pile system increases with the increase of the pile length, The vertical dynamic stiffness value of the end bearing pile system decreases with the increase of pile length, and the vertical dynamic stiffness value of the system tends to be stable when the pile length is 20m.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：U441

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