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近十年来,北京地区在作为基础改革主要方向的钻孔灌注桩基础的勘探、设计、施工和科研方面做了很多工作,工程应用面不断扩大,取得了较好的技术经济效果,积累了一些经验。北京地区地表分布有一层杂填土,因此做天然地基往往要埋置很深,综合技术经济效果较差。改为桩基础后,以第四纪老士,主要是砂卵石层作为桩尖持力层,桩长一般8～10米,其承载力较高,施工速度快,土方量减少,可实现机械化施工,施工面貌得到根本改观。一、发展简况六十年代初,北京地区推广过预制桩,它的承载力大,工程质量好,但造价高,施工有振动。六十年代中,开始研究混凝土灌注桩,做过一些爆扩桩
In the past decade, the Beijing area has done a lot of work in the exploration, design, construction, and scientific research of the bored pile foundation as the main direction of the basic reforms. The application area of the project has continuously expanded, and it has achieved good technical and economic results, and has accumulated some experience. There is a layer of miscellaneous fill on the surface of the Beijing area, so the natural foundation is often buried deeply, and the comprehensive technical and economic effects are poor. After the pile foundation is replaced, the Quaternary magistrate, mainly sand and gravel layer, is used as the pile tip bearing layer, and the length of the pile is generally 8 to 10 meters. The bearing capacity is high, the construction speed is fast, the amount of earthwork is reduced, and mechanization can be realized. Construction and construction have been fundamentally changed. I. Development Profile In the early 1960s, prefabricated piles were promoted in the Beijing area. Its bearing capacity was large and the project quality was good. However, the construction cost was high and there was vibration in the construction. In the 1960s, began to study concrete cast-in-place piles and made some explosion-expanded piles.