【摘要】：主應(yīng)力軸旋轉(zhuǎn)普遍存在于巖土工程中,地基土體經(jīng)歷交通荷載、波浪荷載、多向地震作用等動荷載作用后,作用于土體單元上的主應(yīng)力方向會產(chǎn)生連續(xù)的旋轉(zhuǎn)。主應(yīng)力軸旋轉(zhuǎn)的影響也早已引起了廣大研究者的關(guān)注,隨著空心圓柱扭剪儀在土工試驗(yàn)中的使用,目前國內(nèi)外的研究者對主應(yīng)力軸旋轉(zhuǎn)條件下土體的變形特性和本構(gòu)模擬方面開展了廣泛的研究。主應(yīng)力軸旋轉(zhuǎn)過程中土體的一個重要特性就是塑性應(yīng)變增量方向與應(yīng)力方向不共軸。在實(shí)際工程中,如果忽略土體非共軸特性的影響可能會低估土體的變形而使工程設(shè)計偏于不安全。但目前有關(guān)主應(yīng)力軸旋轉(zhuǎn)的土體非共軸研究主要還是集中在砂土,應(yīng)力路徑也以主應(yīng)力軸小幅旋轉(zhuǎn)為主。無論在試驗(yàn)研究還是理論研究方面對于軟粘土在主應(yīng)力軸連續(xù)純旋轉(zhuǎn)條件下的非共軸變形特性的研究還都比較少。合理考慮土體的非共軸特性對準(zhǔn)確預(yù)測主應(yīng)力軸旋轉(zhuǎn)條件下土體的變形又至關(guān)重要。為此急待豐富與完善考慮主應(yīng)力軸旋轉(zhuǎn)條件下軟粘土非共軸變形特性的研究,以適應(yīng)軟土地區(qū)面臨的越來越復(fù)雜的巖土工程問題。本文在已有研究成果的基礎(chǔ)上,分別從試驗(yàn)研究、規(guī)律分析總結(jié)、模型建立等三個方面開了考慮主應(yīng)力軸連續(xù)旋轉(zhuǎn)影響的軟粘土非共軸變形特性研究。給出了計算主應(yīng)力軸連續(xù)旋轉(zhuǎn)條件下軟粘土非共軸角的計算模型,基于試驗(yàn)研究結(jié)果建立了考慮主應(yīng)力軸旋轉(zhuǎn)引起的軟粘土變形的計算方法。 本文主要研究內(nèi)容和取得的研究成果如下： 1.通過對杭州原狀軟粘土和重塑粘土進(jìn)行的主應(yīng)力軸大幅(180°)連續(xù)純旋轉(zhuǎn)試驗(yàn),重點(diǎn)研究了主應(yīng)力軸連續(xù)旋轉(zhuǎn)條件下軟粘土的非共軸變形特性。分析軟粘土在主應(yīng)力軸單純連續(xù)旋轉(zhuǎn)條件下變形發(fā)展、孔壓累積、剛度衰減等規(guī)律,并從微觀結(jié)構(gòu)層面對主應(yīng)力軸旋轉(zhuǎn)影響機(jī)理進(jìn)行解釋。試驗(yàn)結(jié)果發(fā)現(xiàn)：(1)定向剪切條件下原狀粘土和重塑粘土的非共軸特性都不顯著,隨著剪應(yīng)力增加塑性主應(yīng)變增量方向和主應(yīng)力方向基本趨于共軸；(2)主應(yīng)力軸連續(xù)旋轉(zhuǎn)條件下原狀粘土和重塑粘土存在顯著的非共軸特性,非共軸角隨著主應(yīng)力軸的旋轉(zhuǎn)而波動變化,中主應(yīng)力系數(shù)、剪應(yīng)力水平、循環(huán)旋轉(zhuǎn)次數(shù)和初始各向異性等對軟粘土非共軸特性的影響不顯著,土體非共軸特性主要受應(yīng)力路徑的影響和控制；(3)主應(yīng)力方向的單純改變會引起原狀粘土和重塑粘土顯著的塑性變形累積,隨著主應(yīng)力軸的旋轉(zhuǎn)各應(yīng)變分量也呈波動變化,試樣會由于變形的不斷累積而破壞。中主應(yīng)力系數(shù)對應(yīng)變分量的開展規(guī)律和試樣破壞時的形態(tài)有較大的影響。隨著剪應(yīng)力水平的增加,主應(yīng)力軸單位轉(zhuǎn)幅引起的應(yīng)變也逐漸增加。應(yīng)變的變化規(guī)律與相應(yīng)的應(yīng)力分量變化規(guī)律相似,類似三角函數(shù)曲線,但應(yīng)變曲線要滯后應(yīng)力曲線20°左右；(4)主應(yīng)力方向純旋轉(zhuǎn)也會引起原狀粘土和重塑粘土試樣孔壓的顯著累積,孔壓的累積也隨主應(yīng)力軸的旋轉(zhuǎn)呈波動變化。中主應(yīng)力系數(shù)對孔壓累積速率有一定影響。即使剪應(yīng)力水平很低(q=5kPa,p=150kPa)的條件下,主應(yīng)力軸純旋轉(zhuǎn)也會引起孔壓顯著累積；(5)按常規(guī)的設(shè)計思路,雖然應(yīng)力幅值沒有達(dá)到破壞水平,但是應(yīng)力方向的單純改變也會使土體發(fā)生破壞,并且主應(yīng)力旋轉(zhuǎn)對工程設(shè)計的不利影響還不僅僅體現(xiàn)在變形的累積上,還表現(xiàn)在孔壓累積引起的剛度衰減；(6)從微觀結(jié)構(gòu)角度分析,主應(yīng)力軸旋轉(zhuǎn)引起的土體變形機(jī)理可以歸結(jié)為大主應(yīng)力旋轉(zhuǎn)剪切對土體微觀結(jié)構(gòu)的擾動和破壞,使顆粒發(fā)生破碎或重新排列。 2.通過對現(xiàn)有考慮主應(yīng)力軸純旋轉(zhuǎn)的土體本構(gòu)模型的分析總結(jié)之后發(fā)現(xiàn)只有合理考慮土體非共軸變形特性的本構(gòu)關(guān)系才能較合理地描述試驗(yàn)結(jié)果揭示的土體變形規(guī)律。為此,本文對考慮主應(yīng)力軸旋轉(zhuǎn)復(fù)雜應(yīng)力條件下的軟粘土非共軸塑性流動特性進(jìn)行了深入的研究。借鑒邊界面模型的理論,基于定向剪切試驗(yàn)研究結(jié)果引入橢圓形的原狀粘土破壞邊界面,考慮非共軸塑性應(yīng)變增量切向和法向分量的共同耦合影響,建立了考慮中主應(yīng)力系數(shù)、剪應(yīng)力水平等影響的軟粘土非共軸角計算模型。通過與試驗(yàn)結(jié)果和計算結(jié)果的對比發(fā)現(xiàn),該方法能較好地反映試驗(yàn)研究中得到的粘土非共軸變形規(guī)律。 3.在分析總結(jié)主應(yīng)力軸旋轉(zhuǎn)條件下軟粘土變形特性的基本規(guī)律基礎(chǔ)上,結(jié)合軟粘土的非共軸塑性流動規(guī)律,通過應(yīng)力空間的轉(zhuǎn)換將主應(yīng)力軸純旋轉(zhuǎn)應(yīng)力路徑轉(zhuǎn)換為一種加載方式(應(yīng)變不變量的廣義剪分量)。在廣義塑性理論的基本框架下建立了計算主應(yīng)力軸旋轉(zhuǎn)引起的軟粘土變形的方法�？紤]非共軸的影響對三維條件下Rowe應(yīng)力剪脹關(guān)系進(jìn)行了的修正,在將主應(yīng)變增量轉(zhuǎn)換到一般物理空間坐標(biāo)內(nèi)時,采用考慮非共軸角影響的塑性應(yīng)變增量方向角。最后對計算結(jié)果和試驗(yàn)結(jié)果進(jìn)行了對比驗(yàn)證,表明通過非共軸修正之后的計算結(jié)果與試驗(yàn)結(jié)果更吻合。
[Abstract]:The rotation of the principal stress axis is common in geotechnical engineering. The direction of the principal stress acting on the soil element will produce continuous rotation after the foundation soil undergoes dynamic loads such as traffic loads, wave loads and multi-directional seismic actions. At present, researchers at home and abroad have carried out extensive research on the deformation characteristics and constitutive modeling of soil under the condition of principal stress axis rotation. One of the important characteristics of soil under the condition of principal stress axis rotation is that the direction of plastic strain increment is not coaxial with the direction of stress. The influence of non-coaxial characteristics may underestimate the deformation of soils and make engineering design unsafe. However, at present, the non-coaxial study on the rotation of principal stress axis mainly focuses on sandy soils, and the stress path mainly depends on the small rotation of principal stress axis. There are few studies on the non-coaxial deformation characteristics of soft clay under continuous pure rotation. It is very important to consider the non-coaxial characteristics of the soil properly to predict the deformation of the soil under the condition of principal stress axis rotation. On the basis of existing research results, this paper studies the non-coaxial deformation characteristics of soft clay considering the influence of continuous rotation of principal stress axis from three aspects: experimental study, rule analysis and model establishment. Based on the experimental results, the calculation method of soft clay deformation caused by rotation of principal stress axis is established.
The main contents and achievements of this paper are as follows:
1. The non-coaxial deformation characteristics of soft clay under the condition of continuous rotation of principal stress axes are studied by means of large-scale (180 degrees) continuous pure rotation tests of undisturbed soft clay and remolded clay in Hangzhou. The deformation development, pore pressure accumulation and stiffness attenuation of soft clay under the condition of continuous rotation of principal stress axes are analyzed. The results show that: (1) the non-coaxial properties of undisturbed and remolded clays are not significant under the condition of directional shear, and the incremental direction of plastic principal strain and the direction of principal stress tend to coaxial with the increase of shear stress; (2) the undisturbed clays under the condition of continuous rotation of principal stress axis. The non-coaxial properties of clay and remolded clay are significant. The non-coaxial angles fluctuate with the rotation of the principal stress axis. The influence of the middle principal stress coefficient, shear stress level, cyclic rotation times and initial anisotropy on the non-coaxial characteristics of soft clay is not significant. The non-coaxial characteristics of soil are mainly affected and controlled by the stress path. (3) The principal stress is controlled by the stress path. Simple change of direction will cause significant accumulation of plastic deformation of undisturbed clay and remolded clay. With the rotation of the principal stress axis, the strain components fluctuate, and the specimen will be destroyed due to the accumulation of deformation. With the increase of the force level, the strain caused by the unit rotation of the principal stress axis increases gradually. When the shear stress level is very low (q = 5kPa, P = 150kPa), the pure rotation of the principal stress axis will cause significant accumulation of pore pressure. (5) According to the conventional design, although the stress amplitude does not reach the destructive water However, the simple change of stress direction will destroy the soil, and the adverse effect of principal stress rotation on engineering design is not only reflected in the accumulation of deformation, but also in the stiffness attenuation caused by pore pressure accumulation; (6) From the micro-structure point of view, the deformation mechanism caused by the rotation of principal stress axis can be attributed to the large deformation. The rotation and shear of principal stress disturb and destroy the microstructure of the soil, causing particles to be broken or rearranged.
2. Based on the analysis and summary of the existing constitutive models of soils considering the pure rotation of the principal stress axis, it is found that only the non-coaxial deformation characteristics of soils are reasonably considered can the deformation laws of soils revealed by the test results be described. Therefore, the non-coaxial deformation of soft clays considering the complex rotation of the principal stress axis is discussed in this paper. Based on the theory of boundary surface model and the results of directional shear test, the failure boundary surface of elliptical undisturbed clay is introduced. Considering the coupling effect of tangential and normal components of non-coaxial plastic strain increment, the soft clay considering the influence of middle principal stress coefficient and shear stress level is established. Comparing with the experimental results and the calculated results, it is found that this method can well reflect the non-coaxial deformation law of clay obtained in the experimental study.
3. On the basis of analyzing and summarizing the basic deformation characteristics of soft clay under the condition of rotation of principal stress axis, combined with the non-coaxial plastic flow law of soft clay, the pure rotation stress path of principal stress axis is transformed into a loading mode (generalized shear component of strain invariant) by stress space transformation. A method for calculating the deformation of soft clay caused by the rotation of principal stress axis is established. Considering the influence of non-coaxiality, the stress-dilatancy relationship of Rowe under three-dimensional condition is modified. When the principal strain increment is transformed into general physical space coordinates, the direction angle of plastic strain increment considering the influence of non-coaxial angle is adopted. The experimental results are compared and verified. The results show that the non-coaxial correction is more consistent with the experimental results.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TU44;TU411

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 殷杰;洪振舜;高玉峰;;天然沉積連云港軟黏土的屈服特性[J];東南大學(xué)學(xué)報(自然科學(xué)版);2009年05期

2 童朝霞;張建民;張嘎;;應(yīng)力主軸旋轉(zhuǎn)對波浪作用下堤防變形的影響分析[J];工程力學(xué);2009年10期

3 姜洪偉,趙錫宏;主應(yīng)力軸旋轉(zhuǎn)對軟土塑性變形影響分析[J];上海力學(xué);1997年02期

4 劉元雪,鄭穎人;含主應(yīng)力軸旋轉(zhuǎn)的廣義塑性位勢理論[J];力學(xué)季刊;2000年01期

5 龔曉南,熊傳祥,項可祥,候永峰;粘土結(jié)構(gòu)性對其力學(xué)性質(zhì)的影響及形成原因分析[J];水利學(xué)報;2000年10期

6 韓國城,連鎮(zhèn)營,姚仰平;一個適用于深基坑開挖的三維各向異性模型[J];水利學(xué)報;2002年11期

7 王立忠;李玲玲;;結(jié)構(gòu)性軟土非線彈性模型中泊松比的取值[J];水利學(xué)報;2006年02期

8 魏星;黃茂松;;黏土的各向異性邊界面模型[J];水利學(xué)報;2006年07期

9 黃茂松;孫海忠;錢建固;;粗粒土的非共軸性及其離散元數(shù)值模擬[J];水利學(xué)報;2010年02期

10 沈瑞福，，王洪瑾，周景星;動主應(yīng)力軸連續(xù)旋轉(zhuǎn)下砂土的動強(qiáng)度[J];水利學(xué)報;1996年01期

相關(guān)博士學(xué)位論文 前2條

1 聶影;復(fù)雜應(yīng)力條件下飽和重塑黏土動力特性試驗(yàn)研究[D];大連理工大學(xué);2008年

2 童朝霞;應(yīng)力主軸循環(huán)旋轉(zhuǎn)條件下砂土的變形規(guī)律與本構(gòu)模型研究[D];清華大學(xué);2008年

本文編號：2192094