泥水盾构成膜规律及开挖面稳定性

发布时间：2018-04-29 06:05

本文选题：盾构隧道 + 开挖面稳定　；参考：《浙江大学》2017年博士论文

【摘要】：为了提高居民的出行效率,急需加快城市地下道路网络的建设。盾构隧道施工技术目前在地下交通工程中得到了广泛应用,并向着超深、超大直径方向发展。大直径隧道是城市越江通道的首选方案,但是泥水盾构在穿越江底时容易因为高水压、浅覆土以及河床高渗透性的砂土引发失稳事故。基于实际工程需求,本文对泥水盾构泥膜形成规律和开挖面稳定性两个问题进行了系统深入的研究。主要工作和研究成果如下:(1)采用自行研制的渗透柱开展了不同泥浆压力条件下泥浆渗透试验,研究了泥膜的渗透性与时间的关系,以及泥浆渗透对地层渗透系数的影响。试验结果显示,膨润土质量含量为4.76%的泥浆在71至119 kPa泥浆压力作用下,渗入饱和长江河砂地层(渗透系数为×10-4m/s),渗透开始5 s内,形成微透水的泥膜(35mm等效泥膜渗透系数为7.6×10-5至1.3×10-6m/s);300秒后,才能形成难透水的泥膜(35mm等效泥膜渗透系数为4.4×10-9至7.9×10-9m/s)。盾构在进时,开挖面上只能形成微透水的泥膜。当泥浆压力为71至119 kPa时,泥浆的平均距离范围仅为8.5至21.4 cm。因此,可以认为当D151d85/4.26时泥浆渗透不会改变地层的渗透系数。(2)通过介绍滤饼过滤理论,揭示了泥浆过滤成膜的机理。在泥浆压力10至90 kPa作用下开展了一系列滤失试验,获得了膨润土质量含量为4.76%的泥浆形成的泥膜的本构模型的基本参数(δ =0.2,e0=1.85,α = 2和k0=-5.513)。试验结果显示,泥浆压力越大,形成的泥膜透水性越差。基于滤饼过滤理论的解析解推导,揭示了开挖面上泥膜厚度和渗透系数的动态分布模式。提出了根据泥膜前后压力差计算泥膜平均厚度的方法,发现了泥膜平均厚度与刀臂间的夹角和刀盘转速有关。(3)采用二维数值软件SEEP/W,研究了泥水盾构开挖面前方地层孔压的瞬态分布情况。数值模拟结果显示,有效泥浆压力等于45kPa时,泥膜(35 mm等效泥膜渗透系数为1×10-6m/s)上的孔压迅速下降,长江河砂地层(渗透系数为2×10-4m/s)中孔压缓慢下降,距开挖面30m时达到静水压力。基于开挖面前方土体失稳模式以及土体孔压场,提出了泥膜和地层失稳区域内渗透力的计算方法。结果显示,作用在泥膜和地层失稳区域内的渗透力共同维持开挖面稳定。有效泥浆压力越大,用于支护开挖面稳定的有效泥浆压力的比例越小,支护效率越低。棱柱体和泥膜上的渗透力分别是垂直和水平方向上维持开挖面稳定的主要因素。(4)采用三维数值软件COMSOL,研究了泥水盾构开挖面前方地层总水头的瞬态分布情况。数值模拟结果显示,开挖时间和有效泥浆压力对归一化总水头的分布影响不大。归一化总水头分布显示,泥膜上的渗透力随着地层渗透系数增大而增大,开挖面前方地层渗透力随着地层渗透系数增加而减小,地层渗透系数对开挖面上部地层渗透力影响很小。埋深比对泥膜上总水头的下降幅度及开挖面前方地层中归一化总水头分布情况影响很小,隧道埋深较大时(如C/D2),埋深比对棱柱体上的归一化总水头影响较大。(5)基于极限平衡法建立了极限有效泥浆压力的计算方法。通过比较发现以往研究计算方法获得的有效泥浆压力偏不安全。计算结果显示,有效摩擦角小于25°的地层,且埋深比小于2.5时,归一化极限有效泥浆压力随埋深比增加而显著增加。泥膜渗透系数和地层渗透系数之比与归一化极限有效泥浆压力成正比。有效摩擦角与归一化极限有效泥浆压力成反比;归一化极限有效泥浆压力随着有效粘聚力增加,而线性下降。最后绘制了适用于实际工程的计算图表。
[Abstract]:In order to improve the efficiency of the residents, it is urgent to speed up the construction of the urban underground road network. The shield tunnel construction technology is widely used in the underground traffic engineering, and is developing towards the ultra deep and ultra large diameter. The large diameter tunnel is the first choice for the city crossing channel, but the slurry shield is easy to pass through the bottom of the river. High water pressure, shallow overlying soil and high permeability sand in river bed cause instability accidents. Based on actual engineering requirements, this paper makes a systematic and thorough study on two problems of mud shield mud film formation and excavation face stability. The main work and research results are as follows: (1) different mud pressure conditions are carried out by the self developed permeable column. Under the mud penetration test, the relationship between the permeability and time of the mud film and the influence of mud penetration on the permeability coefficient are studied. The test results show that the mud of 4.76% of bentonite, under the action of 71 to 119 kPa mud pressure, infiltrates into the saturated Changjiang River sand stratum (permeability coefficient is x 10-4m/s), and the permeability begins to be within 5 s, forming a micro permeability. The mud membrane of water (the permeability coefficient of 35mm is 7.6 x 10-5 to 1.3 x 10-6m/s); after 300 seconds the permeable mud film can be formed (the permeability coefficient of 35mm is 4.4 x 10-9 to 7.9 x 10-9m/s). When the shield is entering, the mud membrane can only be formed on the excavation surface. When the mud pressure is 71 to 119 kPa, the average distance range of the mud is only 8.5 To 21.4 cm., it can be considered that mud penetration will not change the permeability coefficient of the formation when D151d85/4.26. (2) through introducing filter cake filtration theory, the mechanism of mud filtration was revealed. A series of filtration tests were carried out under the action of mud pressure 10 to 90 kPa, and the mud film formed by mud of bentonite with the mass content of 4.76% was obtained. The basic parameters of the constitutive model (delta =0.2, e0=1.85, alpha = 2 and k0=-5.513). The results show that the greater the mud pressure is, the worse the permeability of the mud film is. Based on the analytical solution of filter cake filtration theory, the dynamic distribution pattern of the thickness and permeability coefficient of the mud film on the excavation surface is revealed. The average mud film is calculated according to the pressure difference before and after the mud membrane. The thickness method has been found that the average thickness of the mud film is related to the angle between the arm and the blade speed. (3) a two-dimensional numerical software SEEP/W is used to study the transient distribution of the pore pressure in the front of the slurry shield. The numerical simulation shows that the mud film (the permeability coefficient of the 35 mm is 1 x 10-6m/s) when the effective mud pressure is equal to 45kPa. The pore pressure drops rapidly, and the pore pressure of the Changjiang River sand stratum (permeability coefficient is 2 * 10-4m/s) decreases slowly and reaches the static water pressure when it is 30m from the excavation surface. Based on the model of soil instability in front of the excavated surface and the pore pressure field of the soil, the calculation method of the permeability in the mud and stratum instability region is put forward. The result shows that the effect is unstable in the mud film and the stratum. The more effective mud pressure is, the greater the effective mud pressure, the smaller the ratio of effective mud pressure to the stability of the supporting surface, the lower the support efficiency. The permeability on the prism and the mud film is the main factor to maintain the stability of the excavation face in the vertical and horizontal direction respectively. (4) the three-dimensional numerical software COMSOL is used. The numerical simulation results show that the excavation time and the effective mud pressure have little influence on the distribution of the normalized total water head. The distribution of the total head distribution shows that the permeability on the mud film increases with the increase of the permeability coefficient, and the permeability ahead of the front of the excavation face is along with the seepage force. The permeability coefficient of the stratum decreases and the permeability coefficient of the stratum has little influence on the permeability of the upper layer of the excavated surface. The depth of the buried depth has little influence on the decrease of the total head on the mud film and the distribution of the normalized total head in the strata in the front of the excavation. The depth of the tunnel is larger (such as C/D2), and the depth of the buried depth has a better effect on the normalized total water head on the prism. (5) the calculation method of limit effective mud pressure is established based on the limit equilibrium method. By comparison, it is found that the effective mud pressure obtained by the previous research method is not safe. The results show that the effective friction angle is less than 25 degrees and the depth ratio is less than 2.5, and the effective mud pressure of the normalization limit is significant with the depth ratio of buried depth. The ratio of the permeability coefficient to the permeability coefficient of the mud film is proportional to the effective mud pressure of the normalized limit. The effective friction angle is inversely proportional to the effective mud pressure of the normalized limit; the normalized limit effective mud pressure increases with the effective cohesive force and decreases linearly. Finally, the calculation chart for practical engineering is drawn.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：U455.43

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