大直径灌注桩套筒高频振动沉拔特性及其土力学问题

There are always some problems when existing pile driving methods are used for driving and exstrating of sleeves of casting-in-place piles, e.g. the bad influences of pile driving on surroundings, noise as well as low-performance. The using of high frequency vibratory hammers for sleeve driving or exstraing can be effectively performed to solve the problems. However, the mechanisms such as the wave propagation in subsoil and the influence on existing piles in subsoil are unusual complex both in rigid sleeve penetration process and extracting process using high frequency vibratory hammers. It is difficult to calculate the sleeve penetration resistance and the extracting resistance. Both processes can't be simulated availably by using of usual finite element method. If excited force is not large enough to start driving or extracting a sleeve, vibration frequency of vibratory hammers will reduce close to the resonant frequency of subsoils. Consequently, the soil-sleeve-hammer resonance will be produced, which results in adverse environmental influences of dynamic on surroundings. .The aim of the project is to research the vibro-driveability of cylindrical sleeves with open cross-sections and the mechanisms of sleeve extraction in inhomogeneous subsoil. The particle discrete element method (abbr. DEM) will be used to simulate the complex sleeve penetration process and the sleeve extracting process by using high frequency vibratory hammers. It is mainly because of the ability of the particle discrete element to treat the discrete media as an assemblage of granular soils and no constitutive law is required. Nonetheless, the DEM approach can be only used on a microscale. Therefore the new approach coupling between finite and discrete element methods will be developed to model penetration process and extraction process in multi-domains. By applying the new coupled numerical simulation method, near and far field of subsoil are modeled with continuum method and discontinuum method respectively. The below contents will be investigated in details: a). interactions between the subsoil and sleeves, b). influences of strain-softening behaviors of soils on the both processes, c).influence of the thixotropy character of saturated soils on the both processes, d). reconsolidation procedures of soils after the sleeves penetration or extraction, e).development of excess pore pressure, and f). soil plugging inside open-ended sleeves. On the basis of the results from numerical simulation, model experiments and in situ tests will be carried out to investigated the influences of some factors on vibro-driveability of sleeves and the mechanisms of sleeve extracting such as vibration frequency of vibratory hammers, vibrational energy and ground condtions.The new analytical methods will be proposed suitable for calculating the vibro-driveability and extracting of sleeves. The proposed project tends to effectually solved the problems in engineeirng practice.

高频液压振动锤可解决全套管灌注桩基础施工钢护套筒沉拔及取土过程中采用以往施工机械和工艺时存在的问题，对周边振动影响小，噪声小及工效高。但大直径套筒的高频振动贯入与拔出是非常复杂的结构与土相互作用的力学过程。若振动锤激振力不足以启振，机器振动频率降低，土层易产生共振，对周边影响较大。本项目拟引进颗粒离散元方法，克服连续介质力学模型的宏观连续性和本构理论假设，应用离散元与有限元耦合分析技术，既可模拟套管高频振动沉拔的全过程，又可解决离散元计算模型尺度小的问题。通过数值分析研究大直径套筒高频振动贯入与拔出特性及其受软粘土强度软化、重固结及触变性等工程性质的影响、高频振动沉拔过程超静孔隙水压力累积与消散、高频振动作用下套筒内土塞效应。结合模型试验及现场实测研究土层条件，振动频率和激振能量等因素的影响，提出相应的计算模型与理论。通过相关土力学基本理论研究，解决工程实际问题，具有很好的研究意义和价值。

高频液压振动锤可解决全套管灌注桩基础施工钢护套筒沉拔及取土过程中采用以往施工机械和工艺时存在的问题，对周边振动影响小，噪声小及工效高。但大直径套筒的高频振动贯入与拔出是非常复杂的结构与土相互作用的力学过程。若振动锤激振力不足以启振，机器振动频率降低，土层易产生共振，对周边影响较大。本项目研发了全套管大直径振动取土灌注桩施工新技术研发与应用；通过任意欧拉-拉格朗日耦合大变形有限元分析和物理模型试验对套管高频振动沉拔的全过程进行了研究；通过颗粒离散元方法，克服连续介质力学模型的宏观连续性和本构理论假设，应用离散元与有限元耦合分析技术，模拟套管高频振动沉拔的全过程，又可解决离散元计算模型尺度小的问题；通过数值分析研究大直径套筒高频振动贯入与拔出特性、高频振动沉拔过程超静孔隙水压力累积与消散、高频振动作用下套筒内土塞效应；深入地研究了灌注桩套管振动贯入引起的地面振动、对环境影响及隔振措施。提出大直径灌注桩护壁钢套管内的土塞计算模型；Gudehus-Bauer亚塑性本构模型基础上，并引入土塞阻力公式，建立了灌注桩套管振动贯入的运动方程，提出砂性土地基中大直径钢套管高频振动沉贯的计算模型。