Development of Hybrid Foundation consisting of Bearing Piles and a Mat Foundation

建筑物的基础有几种类型，如桩基础、浅基础和浮动基础。虽然浅基础和带有垫板的浮动基础通常比桩基础更经济，但对于这些基础来说，有时很难确保足够的安全系数来抵御软土地基的破坏。另一方面，即使软土地基很厚，桩基支撑的建筑物的沉降也很小。然而，垫层下的桩头经常滑出土中，在地基固结下沉时，有时会受到强烈地震作用的破坏，为了避免这些问题，降低成本，本项目开发了一种由少量承重桩和垫层基础组成的新型复合地基。它的主要功能是同时利用垫板下的软土地基和桩底为PEN…的刚性层的承载能力。更令人震惊。为了确保地基反力作用在垫层基础上，建筑物本身必须与土壤一起下沉。这是因为在桩和垫板之间的桩头安装了“反力控制装置”。在这个项目的第一步，成员们开发了两种“反力控制装置”。第一种是由与垫板连接的三块钢板称为固定板和与桩头连接的两块钢板称为活动板组成。预应力混凝土(PC)螺栓将所有的板连接在一起。然后，在现场安装之前，施加螺栓的轴向力，以在固定板和移动板之间产生较大的摩擦力。当施加在桩上的荷载超过摩擦力的最大限值时，桩开始滑动，但会继续承受等于最大限值的荷载。因此，即使在地基由于固结而下沉时，垫板也保持与土壤的接触和恒定的地基反作用力。第二种是在垫层与桩的连接处采用双钢桩，由于桩与土体之间的负摩阻力，该基础的主要问题之一是应力集中。本工程进行了一系列小规模应力集中试验和大型应力集中试验。小比例尺土工模型为φ=25 cm，h=33 cm，大比例尺为φ=50 cm，h=100 cm。所用桩径分别为19.6 mm和46 mm。根据试验和数值分析结果，充分调动负摩阻力作用于桩上。因此，目前的研究表明，在设计这种混合基础体系时，应考虑最大负摩阻力。较少

There are several types of foundations for buildings, such as pile foundations, shallow foundations, and floating foundations. Although a shallow foundation and a floating foundation with a mat slab are usually more economical than a pile foundation, it is occasionally difficult for these foundations to secure a sufficient safety factor against a failure of soft subsoil. On the other hand, the settlement of a building supported by piles is small even if the soft subsoil is very thick. However, the pile-heads beneath the mat often slip out of the soil, and are sometimes damaged by strong seismic motions when the subsoil subsides due to consolidation.In order to avoid these problems and reduce costs, this project develops a new hybrid foundation consisting of a small number of bearing piles and a mat foundation. Its primary functions are to simultaneously utilize the bearing capacities of both the soft subsoil beneath the mat slab and the rigid layer where the bottom tips of pile are pen … More etrated. In order to secure the subsoil reaction force against the mat foundation, the building itself must subside together with the soil. This is made possible by a "reaction control device" at the head of the pile between the pile and the mat slab.For the first step of this project, members developed two kinds of "reaction control device". The first one is composed of three steel plates called fixed plates connected with the mat slab and two steel plates called movable plates connected with the pile head. A pre-stressed concrete (PC) bolts bind all the plates. The axial force of the bolt is, next, applied to create a large friction force between the fixed plates and the movable plates prior to on-site installation. When the load applied to a pile exceeds the maximum limit of the friction force, the pile starts to slip but keeps supporting a load equivalent to the maximum limit. The mat slab, thus, maintains contact with the soil and a constant subsoil reaction force even when the subsoil settles due to consolidation. The second one is composed of double steel piles at the connection between the mat and a pile.One of the main issues of this foundation is the stress concentration with depth due to the negative friction from the soil to a pile. A series of small scale stress concentration tests and a large scale test were carried out in this project. The soil model of the small scale test is φ =25cm and h=33cm, and the large test scale is φ =50cm and h=100cm. The diameters of piles used are 19.6mm and 46mm, respectively. As the test and numerical analysis results, fully mobilized negative friction force acts on the piles. It was, therefore, made clear from the present study that the maximum negative friction should be taken into consideration in the design of this hybrid foundation system. Less