發(fā)布時間：2018-08-19 15:36

【摘要】：主應力軸旋轉普遍存在于巖土工程中,地基土體經歷交通荷載、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力方向會產生連續(xù)的旋轉。主應力軸旋轉的影響也早已引起了廣大研究者的關注,隨著空心圓柱扭剪儀在土工試驗中的使用,目前國內外的研究者對主應力軸旋轉條件下土體的變形特性和本構模擬方面開展了廣泛的研究。主應力軸旋轉過程中土體的一個重要特性就是塑性應變增量方向與應力方向不共軸。在實際工程中,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計偏于不安全。但目前有關主應力軸旋轉的土體非共軸研究主要還是集中在砂土,應力路徑也以主應力軸小幅旋轉為主。無論在試驗研究還是理論研究方面對于軟粘土在主應力軸連續(xù)純旋轉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確預測主應力軸旋轉條件下土體的變形又至關重要。為此急待豐富與完善考慮主應力軸旋轉條件下軟粘土非共軸變形特性的研究,以適應軟土地區(qū)面臨的越來越復雜的巖土工程問題。本文在已有研究成果的基礎上,分別從試驗研究、規(guī)律分析總結、模型建立等三個方面開了考慮主應力軸連續(xù)旋轉影響的軟粘土非共軸變形特性研究。給出了計算主應力軸連續(xù)旋轉條件下軟粘土非共軸角的計算模型,基于試驗研究結果建立了考慮主應力軸旋轉引起的軟粘土變形的計算方法。 本文主要研究內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行的主應力軸大幅(180°)連續(xù)純旋轉試驗,重點研究了主應力軸連續(xù)旋轉條件下軟粘土的非共軸變形特性。分析軟粘土在主應力軸單純連續(xù)旋轉條件下變形發(fā)展、孔壓累積、剛度衰減等規(guī)律,并從微觀結構層面對主應力軸旋轉影響機理進行解釋。試驗結果發(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,隨著剪應力增加塑性主應變增量方向和主應力方向基本趨于共軸；(2)主應力軸連續(xù)旋轉條件下原狀粘土和重塑粘土存在顯著的非共軸特性,非共軸角隨著主應力軸的旋轉而波動變化,中主應力系數(shù)、剪應力水平、循環(huán)旋轉次數(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力路徑的影響和控制；(3)主應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,隨著主應力軸的旋轉各應變分量也呈波動變化,試樣會由于變形的不斷累積而破壞。中主應力系數(shù)對應變分量的開展規(guī)律和試樣破壞時的形態(tài)有較大的影響。隨著剪應力水平的增加,主應力軸單位轉幅引起的應變也逐漸增加。應變的變化規(guī)律與相應的應力分量變化規(guī)律相似,類似三角函數(shù)曲線,但應變曲線要滯后應力曲線20°左右；(4)主應力方向純旋轉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力軸的旋轉呈波動變化。中主應力系數(shù)對孔壓累積速率有一定影響。即使剪應力水平很低(q=5kPa,p=150kPa)的條件下,主應力軸純旋轉也會引起孔壓顯著累積；(5)按常規(guī)的設計思路,雖然應力幅值沒有達到破壞水平,但是應力方向的單純改變也會使土體發(fā)生破壞,并且主應力旋轉對工程設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)從微觀結構角度分析,主應力軸旋轉引起的土體變形機理可以歸結為大主應力旋轉剪切對土體微觀結構的擾動和破壞,使顆粒發(fā)生破碎或重新排列。 2.通過對現(xiàn)有考慮主應力軸純旋轉的土體本構模型的分析總結之后發(fā)現(xiàn)只有合理考慮土體非共軸變形特性的本構關系才能較合理地描述試驗結果揭示的土體變形規(guī)律。為此,本文對考慮主應力軸旋轉復雜應力條件下的軟粘土非共軸塑性流動特性進行了深入的研究。借鑒邊界面模型的理論,基于定向剪切試驗研究結果引入橢圓形的原狀粘土破壞邊界面,考慮非共軸塑性應變增量切向和法向分量的共同耦合影響,建立了考慮中主應力系數(shù)、剪應力水平等影響的軟粘土非共軸角計算模型。通過與試驗結果和計算結果的對比發(fā)現(xiàn),該方法能較好地反映試驗研究中得到的粘土非共軸變形規(guī)律。 3.在分析總結主應力軸旋轉條件下軟粘土變形特性的基本規(guī)律基礎上,結合軟粘土的非共軸塑性流動規(guī)律,通過應力空間的轉換將主應力軸純旋轉應力路徑轉換為一種加載方式(應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力軸旋轉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應力剪脹關系進行了的修正,在將主應變增量轉換到一般物理空間坐標內時,采用考慮非共軸角影響的塑性應變增量方向角。最后對計算結果和試驗結果進行了對比驗證,表明通過非共軸修正之后的計算結果與試驗結果更吻合。
[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.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TU44;TU411

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本文編號：2192094