桩基础有什么特点?桩基础由哪几部分组成?哪些情况下可以采用桩基础?
推荐回答(3个)
一、桩基础的特点
1)桩支承于坚硬的(基岩、密实的卵砾石层)或较硬的(硬塑粘性土、中密砂等)持力层,具有很高的竖向单桩承载力或群桩承载力,足以承担高层建筑的全部竖向荷载(包括偏心荷载)。(2)桩基具有很大的竖向单桩刚度(端承桩)或群刚度(摩擦桩),在自重或相邻荷载影响下,不产生过大的不均匀沉降,并确保建筑物的倾斜不超过允许范围。(3)凭借巨大的单桩侧向刚度(大直径桩)或群桩基础的侧向刚度及其整体抗倾覆能力,抵御由于风和地震引起的水平荷载与力矩荷载,保证高层建筑的抗倾覆稳定性。(4)桩身穿过可液化土层而支承于稳定的坚实土层或嵌固于基岩,在地震造成浅部土层液化与震陷的情况下,桩基凭靠深部稳固土层仍具有足够的抗压与抗拔承载力,从而确保高层建筑的稳定,且不产生过大的沉陷与倾斜。
二、桩基础一般由桩身、承台或筏板等组成
三、 桩基础设计原则:在天然地基无法满足上部荷载要求,且经过简单人工处理也无法满足的情况下,采用桩基础,利用桩身把荷载力传送到更深的能满足承载要求的地层中去,桩基础是承台、桩间土、桩端持力层共同受力。钻孔灌注桩是在地质条件复杂、持力层埋藏深、地下水位高等不利于人工挖孔及别的工艺成孔的情况下,比较好的工艺选择
桩基的特点:
埋深大,为深基础,将荷载传递桩周土体,或传递到深层强度较高、压缩性较小的稳定土层
承载力大,能承受竖向荷载、水平荷载及动荷载作用
桩基穿过液化土层,可将荷载传递给稳定的不液化土层
具有很大的竖向刚度,桩基沉降小且均匀
具有很大的侧向刚度,能够抵抗台风和地震引起的巨大水平力、上拔力和倾覆力矩,保证高耸结构和高层建筑安全
改变地基土的动力特性,提高地基基础的自振频率,减小振幅,保证机械设备正常运转
避免大量挖方
需要专用设备,造价较高
桩基的适用范围:
主要应用范围
上部软弱土层、下部硬土层,地基不均匀,或特殊地基土(上覆为可液化土、膨胀土等)
高耸结构、重载结构、荷载分布不均匀结构、过近的相邻建筑和较大的地面堆载
精密或大型设备、重要建筑
特殊环境:桥梁、港口等
组成:框架结构:柱下单独布桩,或框架柱列下设基础梁布桩(梁式承台桩基础);
剪力墙结构:墙下设置排桩,一般桩径大于墙厚,需设置构造性过渡梁。桩可预制也可现浇。
桩基具有承载力高、沉降量小而较均匀的特点。桩基在地震力作用下的变形小,稳定性好,是解决地震区软弱地基和地震液化地基抗震问题的一种有效措施。
由承台、桩组成的基础形式,可分为预制桩和灌注桩两大类,适用于需要减少基础振幅、减弱基础振动或控制基础沉降和沉降速率的精密、大型设备的基础。桩基具有承载力高、沉降量小而较均匀的特点,几乎可以应用于各种工程地质条件和各种类型的工程,尤其是适用于建筑在软弱地基上的重型建(构)筑物。因此,在沿海以及软土地区,桩基应用比较广泛。
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