基于离散元法的改性砂卵石土体的流变性能研究

发布时间：2018-07-16 13:44

【摘要】：在土压平衡盾构施工过程中,常常会遇到复杂的工程地质环境,如砂卵石含量相对较高,土体的塑流性较差,从而导致压力舱闭塞、结饼、喷涌以及刀盘磨损严重等技术难题。为了保证盾构施工的正常进行,必须对砂卵石土体进行改良,即向开挖土体中注入改性材料(泥浆、泡沫等),使土体呈现“塑性流动状态”。本文的研究目的是从细观角度对“塑性流动状态”的砂卵石土体进行数值建模,进而分析改性砂卵石土体的流变特性。通过理论分析、室内试验和数值模拟等手段,分别提出了砂卵石颗粒和改性砂浆颗粒之间的本构关系,从而建立了改性砂卵石土体的离散元模型,研究了模型参数的确定方法,设计了相关测试试验,研制了改性砂卵石土体流变性测量装置,分析了改性砂卵石土体的流变特性。对于从细观角度研究改性砂卵石土体流变特性来说,首要内容是对于改性砂卵石土体离散元模型的建立,本文以北京地区某地铁施工现场开挖的砂卵石土体为研究对象,进行了大型三轴试验,获取了不同围压下土体的力学特性,并以此为基础建立了砂卵石土体的离散元模型,应用神经网络对模型参数进行反演,通过不同围压下的数值试验结果与室内试验结果相比较,验证了模型参数的准确性。由于改性砂卵石土体在一定程度上可以看作是砂浆包裹着卵石颗粒的集合体,因此提出了砂浆颗粒的本构关系,建立了砂浆颗粒的离散元模型,通过坍落度、扩展度和V型漏斗试验提出了模型参数的确定方法,并通过直剪试验对所建立模型进行了验证,分析了砂浆的抗剪性能。根据砂卵石土体的特点,研制了改性砂卵石土体流变性测量装置,并对装置进行了标定,获取了不同改良剂添加量下的砂卵石土体流变参数,分析认为改性砂卵石土体属于Bingham流体,用屈服应力和塑性粘度来表征其流变性能,提出了处于“塑性流动状态”砂卵石土体的流变参数范围。根据试验结果建立了搅拌数值模型,通过数值模拟分析了不同压力环境下砂卵石土体的流变参数变化情况。本文对于改性砂卵石土体塑流化的研究,砂卵石地层改良剂的研制,砂卵石土体塑流化改良效果的评价以及盾构施工参数的确定具有重要的指导意义。
[Abstract]:In the process of soil pressure balance shield construction, complex engineering geological environment is often encountered, such as relatively high content of sand and pebble, poor plastic flow of soil, resulting in blockage of pressure chamber, cake formation, spout and serious wear of cutter head and so on. In order to ensure the normal construction of shield tunneling, the sand and gravel soil must be improved, that is to say, the modified materials (mud, foam, etc.) are injected into the excavated soil, so that the soil presents a "plastic flow state". The purpose of this paper is to analyze the rheological characteristics of the modified sandy pebble soil by numerical modeling of the "plastic flow state" sand pebble soil from the viewpoint of meso-scale. By means of theoretical analysis, laboratory test and numerical simulation, the constitutive relationship between gravel particles and modified mortar particles was proposed, and the discrete element model of modified gravel soil was established, and the method of determining model parameters was studied. The rheological properties of modified sandy pebble soil were analyzed. In order to study the rheological properties of modified sandy pebble soil from a meso point of view, the primary content is the establishment of discrete element model of modified sandy pebble soil. In this paper, the sand pebble soil excavated at a subway construction site in Beijing area is taken as the research object. In this paper, the mechanical properties of soil under different confining pressures are obtained through a large-scale triaxial test. Based on this, a discrete element model of sandy pebble soil is established, and the parameters of the model are inversed by neural network. The accuracy of the model parameters is verified by comparing the results of numerical tests under different confining pressures with those of laboratory tests. Because the modified gravel soil can be regarded to some extent as the aggregate of mortar wrapped with pebble particles, the constitutive relation of mortar particles is proposed, and the discrete element model of mortar particles is established. The method of determining the parameters of the model is put forward in the extensibility and V-shaped funnel test. The model is verified by direct shear test, and the shear resistance of mortar is analyzed. According to the characteristics of sandy pebble soil, a rheological measurement device for modified sandy pebble soil was developed and calibrated, and the rheological parameters of sandy pebble soil with different modifiers were obtained. It is considered that the modified sand pebble soil belongs to Bingham fluid, and its rheological properties are characterized by yield stress and plastic viscosity, and the rheological parameters range of sand pebble soil in "plastic flow state" is put forward. Based on the experimental results, a numerical model of mixing was established, and the rheological parameters of sandy pebble soil under different pressure were analyzed by numerical simulation. This paper is of great significance for the study of the plastic fluidization of the modified sand and gravel soil, the development of the improvement agent for the sand and gravel stratum, the evaluation of the effect of the plastic fluidization improvement of the sand gravel soil and the determination of the parameters of shield construction.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U455.43

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