深厚软土地基条件下竖井排水固结法设计计算方法研究

With the continuous rise of construction projects and reclamation projects in coastal areas, the deformation problem for thick soft deposit is increasingly prominent in our country. As a common approach for thick and soft ground treatment, a lot of achievements have been made both in theoretical research and practical application for the vertical drain method. However, it is also found that the design expectation sometimes deviates from the actual situation apparently. The most probable cause is that the existing consolidation theory for vertical drain system assumes the well resistance homogeneous and constant, which fails to reasonably reflect the spatial property and the time-dependent property of the discharge capacity for the plastic drainage board. To this end, the existing relevant researches will be collected and sorted firstly in the research project. Model test for vertical drain system and the discharge capacity test for plastic drainage board under different sizes will be carried out jointly. Correspondingly, the discharge capacity character for plastic drainage board which coincides to the actual situation is gained. Mathematical models for the description of spatial- and time-dependent well resistance will also be proposed. Then, the consolidation theory considered the varied well resistance will be studied in depth under the situations that the load is applied by steps and the vertical drain is partially penetrated into the ground and so on. On this basis, a complete set of design method based on the varied well resistance theory will be set up. Thus, the design method for the ground treatment by vertical drains for thick soft deposit would be more close to the actual situation.

随着我国工程建设的进一步展开和沿海地区围海造地工程的不断兴起，深厚软基问题日益突出。竖井排水固结法作为深厚软基的一种常见处治方法，在理论研究和工程实践方面均已取得大量成果。但同时也发现，由于现有竖井地基固结理论假设竖井井阻均一且恒定，未能合理反映排水板通水量随地基深度变化的空间属性和随固结时间变化的时间属性，导致该法设计预期与实际处治效果存在偏差的现象时有发生。本项目拟在搜集整理现有相关研究资料基础上，首先开展不同尺寸的竖井地基模型试验和排水板通水量联合测试试验，获得与实际情况相吻合的排水板通水量特性，并据此提出随地基深度和固结时间变化的变井阻效应数学模型；然后，系统深入地开展考虑荷载分级施加和竖井未穿透软土层等情况下的考虑变井阻效应的竖井地基固结理论研究；在此基础上，提出一整套基于变井阻固结理论的设计计算方法，从而使深厚软基条件下的竖井排水固结法设计计算方法更贴近于实际情况。

在我国东南沿海地区的工程建设中，深厚软土地基问题突出。竖井排水固结法是深厚软基一种常见处治方法，其理论研究落后于工程实践。现有竖井地基固结理论假设竖井井阻均一且恒定，未能合理反映排水板通水量随地基深度变化的空间属性和随固结时间变化的时间属性，导致该法设计预期与实际处治效果存在偏差的现象时有发生。本项目对现有塑料排水板通水量特性研究进行了综述，发现排水板通水量一方面随侧向压力增大而减小，另一方面在地基固结过程中会因为排水板的弯折和淤积堵塞等影响而逐渐减小。基于这一认识，假定通水量随地基深度线性减小、随时间呈指数函数减小，获得了描述井阻空间属性和时间属性的变井阻效应数学模型。然后，仿效Hansbo和谢康和竖井固结经典理论推导方法，建立了瞬时加荷条件下考虑变井阻效应的固结理论。在此基础之上，推导了考虑土层非线性和变荷载的竖井地基固结解答。另外，考虑到塑料排水板扁平尺寸，基于椭圆假定推导了竖井地基固结理论，并考虑了变井阻影响，使得深厚软土地基条件下的竖井固结理论与实际情况更加吻合。试验研究方面，针对不同型号排水板开展了不同尺寸的竖井地基模型试验，监测了沉降和不同位置的孔隙水压力变化过程，通过反演分析试验数据，得到了模型地基固结性状和塑料排水板的通水量特性，发现用指数衰减函数能较好的描述竖井变井阻效应。另外，将变井阻固结理论应用于模型试验分析和实际工程案例分析，获得了相关参数的取值经验。项目研究成果可供竖井排水固结法设计计算参考。