【摘要】：在含水量高、壓縮性高、抗剪強度低的軟土地基上設置豎井并結合堆載或真空負壓,能加速地基排水固結、提高土體強度、減少構筑物工后沉降和差異沉降。該技術施工簡便、效果可靠且造價低廉,已在公路、鐵路、港口、機場等大型基礎設施建設中廣泛應用。為了合理預測豎井地基的固結發(fā)展,學者們在豎井固結解析解和數值解方面開展了大量研究且已取得大量成果。但同時應看到,目前各種計算方法得到的理論預測值與實測值還有一定差距,對可能的工后沉降和沉降差預測不準。另外,近些年來出現的豎井處理深度加大和工期要求加緊等情況,均給豎井地基的設計計算方法提出了挑戰(zhàn)。為此,本文從解析理論和有限元法兩方面開展了豎井地基固結問題的研究。 (1)首先對以往研究成果從理論方法和參數取值兩方面進行了綜述,結果發(fā)現：目前被國內外廣泛接受的單井地基徑向固結度簡化計算公式均可表述為一個統一的公式,不同方法在涂抹效應和井阻效應的考慮上略有差異；單井固結理論近些年的新進展主要包括非線性理論、非達西滲流理論、考慮涂抹區(qū)滲透性漸變理論以及針對真空預壓法的固結理論等；豎井地基固結分析參數取值方面已經開展了大量研究,但得到的參數取值范圍較大,這將給計算結果的可靠性帶來影響。 (2)通過對現有塑料排水板通水量特性研究進行綜述發(fā)現,排水板通水量一方面隨側向壓力增大而減小,另一方面在地基固結過程中會因為排水板的彎折和淤積堵塞等影響而逐漸減小�；谶@一認識,假定通水量隨地基深度線性減小、隨時間呈指數函數減小,獲得了描述井阻空間屬性和時間屬性的變井阻效應數學模型。然后,仿效Hansbo和謝康和豎井固結經典理論推導方法,建立了瞬時加荷條件下考慮變井阻效應的固結理論。計算分析表明：相對于采用短期通水量恒定值進行計算的豎井固結理論,變井阻固結理論得到的固結速率減緩；當考慮通水量隨地基深度減小時,地基深部土層的超靜孔壓消散變得更加緩慢；當豎井滲透性減小到與井周土體相當,此時豎井不再起排水通道作用,徑向固結將停止。另外,將變井阻固結理論應用于室內大型模型試驗和工程實例分析,結果發(fā)現變井阻理論模擬的結果較傳統理論預測結果與實際情況更為接近。 (3)通過引入Hansbo非達西滲流假定和變滲透系數假定,得到滲流雙重非線性模型。然后,在Biot固結理論研究基礎上,應用加權殘數法推導了考慮該模型的有限元方程,并自編了相應的計算程序。通過開展參數影響分析得到：考慮滲透系數隨時間減小后,地基固結速率減緩趨勢明顯；增大非達西滲流參數m或il,固結發(fā)展速率減緩,但該影響在10%以內；考慮非達西滲流后,地基固結速率隨荷載減小而減緩。 (4)進一步引入土體分段線性e-lgp模型,得到了土體壓縮非線性和滲流雙重非線性模型。然后,結合寧波土樣固結滲流聯合測試試驗,介紹了該模型的參數獲取過程。在給出相應的控制方程和有限元方程基礎之上,詳細闡述了非線性有限元法編程實現過程。最后,通過算例驗證了程序的可靠性,并對考慮土體多重非線性模型時豎井地基的固結性狀進行了較為詳細的分析,獲得了一些有益認識。 (5)對目前廣泛應用的豎井地基平面應變二維等效方法進行了評述。然后,以成層土豎井地基算例和未打穿豎井地基算例對六種二維等效方法進行了考量,結果發(fā)現：地基土成層性對二維等效方法計算結果的可靠性有較顯著影響,而豎井未打穿情況的影響不明顯；在本文算例參數取值情況下,各種方法的誤差情況差別較大,Chai(2001)方法和Tran(2008)方法得到的結果相對可靠。此外,基于等效豎向滲透系數思想,建立了以單元體流量等效的一維變形、一維滲流簡化分析方法。通過算例檢驗發(fā)現,該法計算效率大大提高,但相比于Chai法計算精度并未改善,且計算過程相對復雜。 (6)考慮到豎井地基三維有限元分析計算量大、前處理困難,提出了將井與涂抹區(qū)在地基橫截面內劃分為一個網格的復合單元法。復合單元的未知場由10結點單元和線性插值函數來刻畫。復合單元內部全局坐標結點自由度和局部坐標結點自由度之間的聯系則通過引入經典單井固結解析理論得到建立。之后,基于加權殘數法詳細推導了復合單元法有限元方程,并編制了相應的計算程序。通過對單井地基和群井地基算例進行驗證分析,發(fā)現復合單元法計算精度較高、計算效率也有所改善。 (7)基于大型商業(yè)軟件和自編程序開展了某電廠海堤下豎井地基固結發(fā)展過程的數值模擬。分析過程中,采用Chai(2001)二維等效方法和平面應變空間滲流分析方法分別進行了計算,結果發(fā)現：兩種數值方法模擬得到的地基變形發(fā)展規(guī)律近似一致；后者考慮空間滲流得到的沉降略大、側向位移略�。粌煞N方法的孔壓預測結果差異較為明顯。數值模擬結果還表明：海堤下軟土地基經過塑料排水板處理后,地基固結速率較快,地基中超靜孔壓在各級堆載間歇期均有明顯回落；在給定的堆載方案下,軟土地基變形發(fā)展速率均在控制范圍內。
[Abstract]:Setting vertical wells on soft soil foundation with high water content, high compressibility and low shear strength, combined with loading or vacuum pressure, can accelerate the consolidation of the foundation drainage, improve the strength of soil and reduce the settlement and differential settlement of structures. The technology is simple, reliable and low cost, and has been used in large infrastructure such as highway, railway, port, airport and so on. In order to reasonably predict the consolidation and development of the shaft foundation, a lot of scholars have done a lot of research on the analytical solution and numerical solution of the vertical shaft consolidation, but there have been a lot of achievements. At the same time, it should be seen that there is still a certain gap between the theoretical prediction value and the measured value obtained by various calculation methods at present, and the possible settlement and settlement difference for the possible after work The prediction is not accurate. In addition, in recent years, the depth of shaft treatment and the demand for the construction period have been tightened, all of which have challenged the design and calculation method of the shaft foundation. Therefore, this paper has carried out the study of the consolidation of the shaft foundation from two aspects of the analytic theory and the finite element method.
(1) first of all, the previous research results are reviewed from two aspects of theoretical method and parameter value. It is found that the simplified formula for simplified calculation of radial consolidation of single well foundation, which is widely accepted at home and abroad, can be expressed as a unified formula. Different methods are slightly different in the consideration of the effect of smear effect and well resistance effect; the single well consolidation theory is different. The new progress in recent years mainly includes nonlinear theory, non Darcy percolation theory, the theory of permeation gradient in the smear area and the consolidation theory for vacuum preloading. A lot of research has been carried out on the parameter value of the consolidation analysis of vertical shaft foundation, but the range of parameters obtained is large, which will give the reliability of the calculation results. Impact.
(2) through the study of the current water flow characteristics of the existing plastic drain board, it is found that the water flow rate of the drainage plate decreases with the increase of lateral pressure, on the other hand, it will decrease gradually in the consolidation process of the foundation because of the influence of the bending of the drain plate and the clogging of the silt. The time exponential function decreases, and the mathematical model of the variable well resistance effect is obtained to describe the spatial and temporal properties of the well resistance. Then, the consolidation theory which considers the change of the well resistance effect under the instantaneous loading condition is modeled after the classical theoretical derivation of the Hansbo and Xie Kang and the vertical shaft consolidation. The consolidation theory obtained by the value is calculated, and the consolidation rate of the variable well resistance consolidation theory slows down. When the water flow is reduced with the depth of the foundation, the excess pore pressure dissipation of the deep soil layer becomes more slow; when the shaft permeability is reduced to the surrounding soil, the vertical well does not play the drainage channel, and the radial consolidation will stop. In addition, the theory of variable well resistance consolidation is applied to large-scale indoor model test and engineering case analysis. It is found that the result of the theory of variable well resistance is closer to the actual situation than that of the traditional theory.
(3) through the introduction of the Hansbo non Darcy percolation hypothesis and the assumption of variable permeability coefficient, the seepage double nonlinear model is obtained. Then, on the basis of the Biot consolidation theory, the finite element equation considering the model is derived by using the weighted residual method, and the corresponding calculation program is made up. By the analysis of the parameter influence, the permeability coefficient is considered. The consolidation rate slowed down with time, and the consolidation rate slowed down with the increase of non Darcy percolation parameters m or IL, but the effect was less than 10%. The consolidation rate of foundation slowed down with the decrease of load.
(4) further introducing the piecewise linear e-lgp model of soil, the nonlinear and percolation nonlinear model of soil compression is obtained. Then, combined with the combined test test of Ningbo soil sample consolidation seepage, the parameter acquisition process of the model is introduced. On the basis of the corresponding control equation and the finite Yuan Fangcheng Foundation, the nonlinear finite element is expounded in detail. In the end, the reliability of the program is verified by an example, and the consolidation behavior of the shaft foundation is analyzed in detail in the consideration of the multiple nonlinear soil model, and some useful understanding is obtained.
(5) the two-dimensional equivalent method of plane strain of shaft foundation, which is widely used at present, is reviewed. Then, six two dimensional equivalent methods are considered by taking the example of vertical well foundation and the example of not wearing the shaft foundation. The results show that the foundation soil stratification has a significant influence on the reliability of the calculation results of the two-dimensional equivalent square method. It is not obvious that the impact of the well is not worn; in this paper, the error conditions of various methods are different, the results obtained by the Chai (2001) method and the Tran (2008) method are relatively reliable. In addition, based on the idea of the equivalent vertical permeability coefficient, a one-dimensional deformation of one dimensional flow and a one-dimensional seepage analysis is established. The computational efficiency of this method is greatly improved, but the computational accuracy is not improved compared with Chai method, and the computational process is relatively complicated.
(6) considering that the three-dimensional finite element analysis of the shaft foundation is large and the preprocessing is difficult, a composite element method is proposed to divide the well and the smear area into a grid in the cross section of the foundation. The unknown field of the composite element is depicted by the 10 node element and the linear interpolation function. The degree of freedom and the local coordinate of the global coordinate node in the composite element are also described. The connection between point freedom is established by introducing the classical single well consolidation theory. Then, based on the weighted residual method, the finite element equation of the composite element method is derived in detail, and the corresponding calculation program is compiled. The efficiency has also improved.
(7) based on the large-scale commercial software and self compiled program, the numerical simulation of the consolidation and development process of the subgrade foundation under the sea embankment of a power plant is carried out. In the analysis process, the Chai (2001) two dimensional equivalent method and the plane strain spatial seepage analysis method are respectively calculated. The results are found: the development law of the foundation deformation simulated by the two numerical methods The settlement of the two methods is more obvious. The results also show that the consolidation rate of the foundation under the soft soil foundation under the sea embankment is faster after the plastic drainage plate is treated by the plastic drainage plate, and the hyper static pore pressure in the foundation is obvious in the batch period. Under the given surcharge plan, the rate of deformation development of soft soil foundation is within the control range.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2013
【分類號】：TU472

【引證文獻】

相關期刊論文 前1條

1 劉忠玉;焦陽;;考慮Hansbo滲流的砂井地基徑向固結分析[J];鄭州大學學報(理學版);2014年02期

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本文編號：2172426