本文選題：非飽和土　切入點：SWCC　出處：《大連理工大學》2013年博士論文

【摘要】：無論是受不斷出現(xiàn)的實際工程問題的驅使還是遵循從簡單到復雜的科學發(fā)展規(guī)律,當前土力學研究的焦點已轉向更為廣泛也更具代表性的非飽和土領域。目前,基于重塑試樣的室內試驗是研究非飽和土的主要手段之一,而對于試驗設備昂貴、試驗耗時嚴重的非飽和土研究,試樣是否均一已成為非飽和土試驗結果能否有效應用與分析、研究的關鍵性問題。傳統(tǒng)觀念認為相同制樣條件下的重塑試樣都是均一的,但這些試樣在非飽和條件下卻可能因孔隙結構的不同而產生差異,而這種差異在實際研究中并未考慮。本文從理論分析出發(fā),通過壓力板儀測量多個試樣的土水特征曲線(SWCC),確定相同基質吸力下試樣的平衡飽和度存在差異,即試樣在非飽和狀態(tài)下并不均一；根據直剪試驗確定試樣平衡飽和度差異將對試樣的力學性質造成影響；通過調整初始制樣條件,改善試樣均一性,分析土水特征曲線的變化以及試樣尺寸的影響,并對試驗過程中影響土水特征曲線的各種因素進行分析總結；綜合考慮脫濕試驗和無側限抗壓強度試驗的結果,分析飽和度-時間關系曲線與非飽和土試樣力學性質之間的關系,根據研究成果提出非飽和土試樣均一性的判別準則；根據非飽和土試樣均一性的判別準則對試樣進行優(yōu)選,采用二次改進的“土工靜力-動力液壓三軸-扭轉多功能剪切儀”對優(yōu)選試樣進行循環(huán)加載試驗,分析循環(huán)荷載作用下非飽和土試樣的累積變形、動孔隙水壓力、體變等與循環(huán)應力、基質吸力、固結壓力的關系。基于上述研究,得到如下結論： (1)通過雙孔隙模型,從理論角度分析得出同一基質吸力下試樣可能具有明顯不同的平衡飽和度；對四個三軸試樣的SWCC進行對比分析,證實平衡飽和度差異的確存在。擬合結果表明由于引入修正系數(shù)C(ψ),因此FredlundXing模型更為合理�；趬毫Π鍍x與直剪儀的組合試驗證實平衡飽和度差異對試樣的力學性質將產生影響,因此必須重視平衡飽和度差異的影響。 (2)通過改變試樣的初始條件,可以在一定程度上減弱試樣差異性對SWCC的影響,即試樣均一性提高,但是這種試樣差異性仍難以消除。同時,試驗結果表明：顆粒級配不良也將引起孔隙分布不均,導致在一定基質吸力范圍內SWCC的差異明顯；蒸發(fā)效應在壓力板儀試驗中持續(xù)存在,并在平衡后期成為失水的重要因素；高徑比較大的試樣對側面防護有明顯的依賴性,在沒有側面防護時,蒸發(fā)將成為失水的主要因素,因此筆者認為在非飽和土研究中采用完整的亞克力制作的重塑筒作為側面防護值得推廣。 (3)根據脫濕試驗與無側限抗壓強度試驗的結果,對飽和度-平衡時間關系曲線和非飽和土試樣力學性質之間的關系進行對比分析,結果表明：當試樣的飽和度-平衡時間關系曲線一致時,它們力學性能以及孔隙結構幾乎一致,可認為這些試樣是均一的；在相同基質吸力下,平衡飽和度較低的試樣具有更穩(wěn)定的力學性質�；谏鲜鼋Y論提出非飽和土試樣均一性的判別準則,并指出應選用平衡飽和度較低的試樣。通過總結制樣方法以及土的基本特性,針對制樣不均、干密度難以控制、試樣在包裹橡膠膜等過程中易受擾動等問題,設計了解決上述問題的三軸制樣器。該三軸制樣器將對開模定位、密封合為一體,提高試樣尺寸精度與密封效果；通過兩級控制模式保證試樣的干密度；并通過對開模保護試樣,消除了額外擾動對試樣的影響。 (4)對臨界循環(huán)應力作用下的累積變形進行研究,結果表明：隨著基質吸力的增大,試樣的累積應變逐漸減小,并趨于穩(wěn)定；在基質吸力一定時,試樣累積應變隨固結壓力的增大而增大。進一步分析表明在指定固結壓力下,非飽和土試樣的初始應變與累積應變的比值為一定值,而初始應變與基質吸力呈線性關系,因此可根據飽和試樣的初始應變預測一定基質吸力范圍內的非飽和土試樣在臨界循環(huán)應力作用下的累積應變。 (5)對100kPa基質吸力和100kPa固結壓力下的累積變形進行研究,結果表明：在特定基質吸力范圍內,拉伸破壞將成為非飽和土試樣動力失穩(wěn)的主要因素,并且土體薄弱處成為拉伸破壞發(fā)生的主要區(qū)域；拉伸破壞與循環(huán)應力密切相關,同時拉伸破壞也明顯受到基質吸力的制約,因此試樣累積變形與基質吸力未呈現(xiàn)單調變化,而是受到循環(huán)應力與基質吸力綜合作用,即拉伸破壞不存在基質吸力的臨界值,而是隨基質吸力增大出現(xiàn)拐點,這里將基質吸力的拐點定義為關鍵基質吸力。在本次試驗中的關鍵基質吸力為100kPa。 (6)從循環(huán)應力、基質吸力、固結壓力三方面對循環(huán)荷載作用下的孔隙水壓力與體變進行對比分析,研究表明：非飽和土的孔隙水壓力受到基質吸力的明顯影響；在低基質吸力下,非飽和土試樣性質近似于飽和土,依然會產生超孔隙水壓力,并表現(xiàn)出隨循環(huán)應力增大而增大的趨勢,但在高基質吸力下其變化明顯受限,隨循環(huán)應力增大規(guī)律性并不明顯。非飽和土試樣的體變受循環(huán)應力影響明顯,特別在rc=0.9時由試樣由體縮突變?yōu)轶w脹,并且這種變化不受基質吸力和固結壓力的影響,這一現(xiàn)象進一步表明拉應力對非飽和土的影響顯著。
[Abstract]:Whether it is driven by the emergence of practical engineering problems or follow the scientific development rule from simple to complex, the current focus of the study of soil mechanics has shifted to broader and more representative of the unsaturated soil. At present, the indoor test sample based on remodeling is one of the main means of unsaturated soil, and for the test equipment is expensive, time-consuming test of unsaturated soil research, if the specimen has become uniform unsaturated soil test results can be effective application and analysis, a key problem in the research. The traditional idea that the remolded samples under the condition of the same sample preparation is homogeneous, but these samples in non saturated conditions may produce difference because the pore structure is different, and the difference in the actual research is not taken into account. Based on the theoretical analysis of the soil water characteristic curve measurement of multiple samples by the pressure plate instrument (SWCC),. The balance of the saturation of sample under the same matric suction are different, the sample is not uniform in the unsaturated state; according to the direct shear test to determine the sample equilibrium saturation difference will affect the mechanical properties of the sample; by adjusting the initial conditions of sample preparation, improve sample homogeneity, change analysis of soil water characteristic curve and the influence of the specimen size and various factors which affect the soil water characteristic curve during the test were analyzed and summarized; considering the wetting test and unconfined compressive strength test results, analysis of the relationship between saturation time curve and unsaturated soil mechanical properties, according to the research results of unsaturated soil sample homogeneity criterion; according to the non saturated soil sample homogeneity criterion to optimize the sample, using two improved soil static and dynamic universal triaxial and torsional power three Cyclic shear tests were carried out on the selected samples. The cumulative deformation, the dynamic pore water pressure and the volumetric strain of unsaturated soil samples under cyclic loading were related to the cyclic stress, the matrix suction and the consolidation pressure. Based on the above research, the following conclusions were reached.
(1) through the double porosity model from the angle of theory analysis, it is concluded that the same suction specimens under different saturation may have obvious balance; on the four axis three specimens of SWCC were analyzed, confirmed the equilibrium saturation differences do exist. The fitting results show that due to the introduction of the correction coefficient C (PSI), so the FredlundXing model is more reasonable combination test. The pressure plate instrument and direct shear apparatus that mechanical properties of equilibrium saturation differences on the specimen will have an impact on, so we must attach importance to the influence of equilibrium saturation difference.
(2) the change of the initial conditions, can affect the sample difference of SWCC decreases to a certain extent, the homogeneity of the sample increased, but the difference of the sample is still difficult to eliminate. At the same time, experimental results show that the particle size distribution is bad will cause uneven distribution of pore, lead to differences in SWCC in a certain range of matric suction the obvious; evaporation effect persists in pressure plate test, and become an important factor in the water balance later; samples of high diameter is significantly dependent on side shields, with no side door, evaporation will become the main factor of water loss, so I think in the study of unsaturated remodeling tube the soil with complete production of acrylic as a side door is worthy of promotion.
(3) according to the desorption test and unconfined compressive strength test results of saturation equilibrium time curve and unsaturated soil samples the relationship between mechanical properties were analyzed, the results show that when the sample saturation equilibrium time curve is consistent, their mechanical properties and pore structure can be almost the same. Think of these specimens is uniform; under the same suction, the sample equilibrium saturation with lower mechanical properties more stable. Based on the above conclusion to put forward the criterion of unsaturated soil sample homogeneity, and points out that we should choose sample equilibrium saturation is low. By summarizing the characteristics of sample preparation method and system for soil. Not all, dry density is difficult to control, the disturbed sample problems such as the package rubber membrane process, three axis sample making device to solve the above problems. The design of three axis sample making device of mold Positioning, sealing and integration as a whole, improve the size accuracy and sealing effect of the sample, ensure the dry density of the sample through the two level control mode, and eliminate the influence of additional disturbance on the specimen by opening the mold to protect the sample.
(4) the critical cyclic stress accumulation under the action of stress deformation was studied. The results show that with the increase of suction, cumulative strain of specimen decreases, and tends to be stable; in some specimens of matric suction, cumulative strain with the consolidation pressure increases. Further analysis showed that in the specified consolidation pressure, the ratio of the initial strain and strain accumulation of unsaturated soil samples to a certain value, and the initial strain and the matrix suction is linear, so according to the initial strain of saturated prediction of the matric suction range of unsaturated soil samples in the critical cyclic stress strain under the action of force.
(5) the cumulative 100kPa matric suction and 100kPa consolidation deformation under pressure is studied, the results showed that: in particular the matric suction range, the tensile failure of unsaturated soil specimen power will become the major factor for instability, and weak soil become the main area of tensile failure occurs; tensile failure and cyclic stress is closely related. At the same time, the tensile failure also obviously constrained by the matrix suction, so the sample cumulative deformation and suction is not monotonic, but under cyclic stress and matric suction, the critical value of tensile failure does not exist in the matric suction, but with the increase of matric suction inflection point, here will be defined as the key point of suction suction the key of matric suction in this experiment is 100kPa.
(6) from the cyclic stress, matrix suction and consolidation pressure of three aspects of comparative analysis, the cyclic loading of pore water pressure and volume change study shows that the effect of pore water pressure of unsaturated soil by suction; in low suction, unsaturated soil specimen properties similar to the saturated soil still, will produce excess pore water pressure, and with the cyclic stress increasing, but at high matric suction changes under cyclic stress was limited, with increasing regularity is not obvious. The volume change of unsaturated soil specimen under cyclic stress significantly, especially in the rc=0.9 by the sample by volume contraction for expansion and mutation, this change is not affected by the influence of matric suction and consolidation pressure, this phenomenon further showed that the influence of tensile stress on unsaturated soil significantly.

【學位授予單位】：大連理工大學
【學位級別】：博士
【學位授予年份】：2013
【分類號】：TU41

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