层状土的固结特性研究
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摘要
土的固结特性研究是土力学的基本课题之一。土体是多相体，又是自然历史的产物，土体的变形规律比较复杂，这些决定了土体固结过程的复杂性。土体在固结过程中，随着土中水的排出，土体孔隙比减小，土体产生压缩，体积变小；随着有效应力逐步增大，土体抗剪强度提高。工程中常常应用固结过程这两种特性通过排水固结法对地基特别是软粘土地基进行改良，达到提高地基承载力、减少工后沉降的目的。
层状土是由多种不同属性、不同厚度、不同组分按某种方式组合而成的天然层状体，在长期的地质作用、地应力作用、水与温度以及人为作用下，使得土内产生了微细观损伤与宏观断裂面，因而其特性显著不同于单层土。在地基工程、道路工程及边坡工程等实际地下工程结构设计与施工中大量存在着层状土问题。各种工程受到层状土的强度、变形、破坏等性质的影响，常造成建筑地基变形过量、路基不均匀沉降和边坡滑移等岩土工程失稳及灾害事故的频繁发生。因此，研究层状土的固结特性既有理论意义，又有实际应用方面的意义。
本文以都汶高速公路层状路基为工程背景，首先根据Biot平面固结方程，运用积分变换和矩阵传递的方法，研究了层状土的二维Biot固结问题，根据下边界为不透水基岩的边界条件，获得了土体表面作用荷载时，任意点应力、位移的一般积分形式解；然后将工程现场地质分析和室内试验相结合，测定路基和路堤填土的各种基本物理性质指标；再结合本文研究内容，应用有限元分析软件Adina，建立有限元模型。通过控制单元的生死来实现路堤填土的逐步加载，得到沉降一时间关系曲线、土中超静孔隙水压力消散曲线、水平面的沉降曲线和侧向变形图等；最后与实测数据对比，发现吻合较好。
研究结果表明：层状路基在路堤逐步填土荷载作用下沉降在空间上堤趾以内路基大多下沉，堤趾以外则多为向上隆起，而且随着深度的增加，沉降和隆起都在减小，在时间上随着时间的增加，沉降逐渐增大，而隆起先增大后减小；孔隙水压力的消散在空间上填土区以内和地基深处消散较慢，在时间上总体看在进行，但存在一定波动；侧向变形在竖直方向上随深度增加而增加，在水平方向上堤趾附近最大，两侧减小，在时间上填土刚结束时达最大，之后略有减小。
Study on the consolidation characteristics of soil is one of basic tasks in soil mechanics. Soil is multi-phase and natural-historical, so it decides that the process of consolidation is complicated. During this process, water in the soil will be discharged accompany with void ratio decreasing, and the volume will be compressed and become smaller, the effective stress will increase, and shear strength be improved These characteristics of consolidation usually are used in engineering to improve bearing capacity and decrease settlement of foundation especially soft one.
Layered soils are made of different attributes and thicknesses and components which were assembled according to some ways. Under long geologic effect, in situ stress, water, temperature and man-made effect, microcosmic damage and macrostructure were brought in soils, so their characteristics are very different from single soil. There are lots of layered-soils problem in design and construction of practical underground engineering such as foundation, road and slope. Instability and disaster of geotechnical engineering like differential settlement of foundation and sliding slope usually are encountered due to strength, deformation and breakage of layered soils. So there are theoretical and practical significance of this paper.
The layered-soil ground of Du Jiangyan-Wen Chuan's expressway is engineering background of this paper. Firstly, according to Biot 2-D consolidation equation, author study the 2-D Biot consolidation problem using integral transform and matrix transfer. When lower boundary is rock, stress and displacement of any point in ground are got Then, combination geology analysis with laboratory test, some parameters of ground and filling of embankment are got Then, Adina which is a kind of FEA software is introduced simplely. Then, model of Finite Element is established by controlling the birth time of element to achieve to load step by step. The curve of settlement-time, pore pressure-time and Y-displacement-time are got. At last, contrasts with data from field were carried out, which were validated preferably.
It was revealed by the research result that settlement of layered-soil ground most is down within embankment, whereabouts is up. Settlement and heave decrease with the depth increasing. From time settlement increase with time increasing, however heave become larger firstly and smaller lastly. The dissipation of pore pressure is slower within embankment and deeper position, and it is going along with time, but there is some fluctuation. Y-displacement is larger when deeper, and it is the largest near embankment from horizontal direction. From time it is the largest when load is over, and then decrease a little.
层状土是由多种不同属性、不同厚度、不同组分按某种方式组合而成的天然层状体，在长期的地质作用、地应力作用、水与温度以及人为作用下，使得土内产生了微细观损伤与宏观断裂面，因而其特性显著不同于单层土。在地基工程、道路工程及边坡工程等实际地下工程结构设计与施工中大量存在着层状土问题。各种工程受到层状土的强度、变形、破坏等性质的影响，常造成建筑地基变形过量、路基不均匀沉降和边坡滑移等岩土工程失稳及灾害事故的频繁发生。因此，研究层状土的固结特性既有理论意义，又有实际应用方面的意义。
本文以都汶高速公路层状路基为工程背景，首先根据Biot平面固结方程，运用积分变换和矩阵传递的方法，研究了层状土的二维Biot固结问题，根据下边界为不透水基岩的边界条件，获得了土体表面作用荷载时，任意点应力、位移的一般积分形式解；然后将工程现场地质分析和室内试验相结合，测定路基和路堤填土的各种基本物理性质指标；再结合本文研究内容，应用有限元分析软件Adina，建立有限元模型。通过控制单元的生死来实现路堤填土的逐步加载，得到沉降一时间关系曲线、土中超静孔隙水压力消散曲线、水平面的沉降曲线和侧向变形图等；最后与实测数据对比，发现吻合较好。
研究结果表明：层状路基在路堤逐步填土荷载作用下沉降在空间上堤趾以内路基大多下沉，堤趾以外则多为向上隆起，而且随着深度的增加，沉降和隆起都在减小，在时间上随着时间的增加，沉降逐渐增大，而隆起先增大后减小；孔隙水压力的消散在空间上填土区以内和地基深处消散较慢，在时间上总体看在进行，但存在一定波动；侧向变形在竖直方向上随深度增加而增加，在水平方向上堤趾附近最大，两侧减小，在时间上填土刚结束时达最大，之后略有减小。
Study on the consolidation characteristics of soil is one of basic tasks in soil mechanics. Soil is multi-phase and natural-historical, so it decides that the process of consolidation is complicated. During this process, water in the soil will be discharged accompany with void ratio decreasing, and the volume will be compressed and become smaller, the effective stress will increase, and shear strength be improved These characteristics of consolidation usually are used in engineering to improve bearing capacity and decrease settlement of foundation especially soft one.
Layered soils are made of different attributes and thicknesses and components which were assembled according to some ways. Under long geologic effect, in situ stress, water, temperature and man-made effect, microcosmic damage and macrostructure were brought in soils, so their characteristics are very different from single soil. There are lots of layered-soils problem in design and construction of practical underground engineering such as foundation, road and slope. Instability and disaster of geotechnical engineering like differential settlement of foundation and sliding slope usually are encountered due to strength, deformation and breakage of layered soils. So there are theoretical and practical significance of this paper.
The layered-soil ground of Du Jiangyan-Wen Chuan's expressway is engineering background of this paper. Firstly, according to Biot 2-D consolidation equation, author study the 2-D Biot consolidation problem using integral transform and matrix transfer. When lower boundary is rock, stress and displacement of any point in ground are got Then, combination geology analysis with laboratory test, some parameters of ground and filling of embankment are got Then, Adina which is a kind of FEA software is introduced simplely. Then, model of Finite Element is established by controlling the birth time of element to achieve to load step by step. The curve of settlement-time, pore pressure-time and Y-displacement-time are got. At last, contrasts with data from field were carried out, which were validated preferably.
It was revealed by the research result that settlement of layered-soil ground most is down within embankment, whereabouts is up. Settlement and heave decrease with the depth increasing. From time settlement increase with time increasing, however heave become larger firstly and smaller lastly. The dissipation of pore pressure is slower within embankment and deeper position, and it is going along with time, but there is some fluctuation. Y-displacement is larger when deeper, and it is the largest near embankment from horizontal direction. From time it is the largest when load is over, and then decrease a little.
引文
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[36] 金问鲁，二粘土固结与次时间效应间题解，岩土工程学报，Vol．2，No．2。
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[2] Rerdulic L, Porenziffer and Porenwasserdilick in Tonen, Bauingenieur, Vol.17, 1936
[3] Blot M.A, General theory of three-dimensional consolidation, Jour.Appl.Phys, Vol.12,1941
[4] Biot M.A, Consolidation settlement under a rectangular load distribution, Jour.Appl.Phys,Vol. 12, 1941
[5] Wilson, N. E. and Elgohary, M. M., Consolidation of soils under cyclic loading Canadian Ceotechnical Journal, Toronto, Ontario, Canada, Vol.Ⅱ, No.3 pp. 420-423.
[6] Baligh, M. M and Levadoux, J.N. Nonlinear consolidation theory for cyclic loading,Research Report R77-I0, Order No.568, Department of Civil Engineering, Massachusetts Institute of Technology, Cambridge, mass, Mar., 1977.
[7] Baligh, M.M.and Levadoux, J.N. Consolidation theory for cyclic loading, Journal of the Geotechnical Engineering Division, ASCE. pp415-431.
[8] Yang, J. and Wu, S. M., One-dimensional consolidation of layered saturated soils under cyclic loading,Proc. of Int. Symposium on Compression and Consolidation of layered soik Vol.2, A. A. Balkema Publisher, Rotterdam.
[9] Wu, S. M and Yang,J., A study on three-dimensional consolidation of layered saturated soils, Proc. of int Symposium on Compression and Consolidation of layered soils, Vol 2, A. A Balkema Publisher,Rotterdam.
[10] 陈宗基，粘土层沉暇由于固结和次时间效应)的二维问题，力学学报，Vol．2，No．1。
[11] 陈宗基，固结及次时间效应的单向问题，土木工程学报，Vol．5，No．1．
[12] 门福录，粘-弹-塑性体的应力松弛，力学学报，Vol．5，No．4．
[13] 门福录，粘土固结与次时间效应单维问题的近似解，水利学报，No．1．
[14] 赵维炳，广义Voigt模型模拟的饱水土体—维固结理论及其应用，岩土工程学报，Vol．11，No．5．
[15] 王盛源，变荷载下的粘弹性体—维固结问题，水利水运科学研究，第二期。pp．10-17．
[16] 杨丹，吴世明，陈龙珠，循环荷载下饱和粘土的维粘弹塑性解答，水利学报，No．5。
[17] Gray, H., Simulataneous consolidation of contiguous layers of unlike compressible soils, Trans. ASCE, Vol.110.
[18] Schiffman, R. L. and Fangaroli A. A, Consolidation due to tangential loads, Proc. 4thICSMFE.
[19] Schiffman, R. L. and Stein, J. R. One-dimensional consolidation of layered systems. JSMFD, ASCE, Vol.69,No.4. pp. 1499-1504.
[20] 陈根媛，多层地基的—维固结计算方法与沙井地基计算的改进建议，水利水运科学研究，No．2，pp．1-13。
[21] Lee P.K. K., Xie K H, Cheung Y. K. A study on one dimemsional consolidation of layered systems, Int. J. for Numerical and Analytical Methods in Geomechanics Vol.16,pp.815-832.
[22] 谢康和，施淑群，潘秋元，双层地基固结实用计算理论与曲线(一)，地基处理，Vol．4，No．4．pp．1-14。
[23] 谢康和，施淑群，潘秋元，双层地基固结实用计算理论与曲线(二)，地基处理，Vol．5，No．2，pp．21-32。
[24] 谢康和，双层地基—维固结理论与应用，岩土工程学报，Vol．16，No．5，pp．24-35。
[25] 谢康和，潘秋元，变荷载下任意层地基—维固结理论，岩土工程学报，Vol．17，No．5，pp．82-87。
[26] 杨峻，吴世明，循环荷载作用下层状饱和土体的—维固结分昕，结构与地基国际学术研讨会论文集，浙江人学出版社。
[27] 弗洛林，《土体压密理论》，水利电力出版社，1960．
[28] Davis, E. H. and Poulos, H. G, The use of elastic theory for settlement prediction under three-dimensional conditions,Geotechnique Vol. 18, No. 1.
[29] Davis, E. H. and Poulos, H. G , Rate of settlement under two and three-dimensional conditions, Geotechnique, Vol.22, No. 1.
[30] Christian. J. T. et. at., Consolidation of a layer under a strip load, Proc. ASCE, JSMFD, Vol.98, SM7.
[31] Booker, J. R. , Two-dimensional consolidation on limited clay stratum. Int. J. of solid. structure.
[32] Gibson,R. E, and Mc Namee, J., The consolidation settlement of a load uniformly distributed over a rectangular area, Proc. 4th ICSMfe, Vol. 1.
[33] J. Mc Namee & R. E. Gibson, Displacement Function and Linear Transforms applied to diffusion through porous elastic media, Q. J. Mech. Appl. Math., 13.1960,98-111.
[34] Gibson,R. E. et al., The theory of one-dimensional consolidation of saturated clays. I. Finite non-linear consolidation of thin homogeneous layers,Geotechnique, Vol. 17,No.3.
[35] Gibson, R. E. et al., Plane strain and axially symmetric consolidation of a clay layer on a smooth impervious base, J. Mech. Appl. Math. Vol.23.
[36] 金问鲁，二粘土固结与次时间效应间题解，岩土工程学报，Vol．2，No．2。
[37] 黄传志，多维太沙基固结微分方程求解，岩土工程学报，Vol．13，No．1。
[38] 黄传志，肖原。二维固结问题的解析解。岩土工程学报，1996 18(3)：47-54。
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