推荐回答(3个)
有三种:一是整体剪切破坏,二是局部剪切破坏,三是冲剪破坏(又称刺入剪切破坏)。
(a)地基破坏的模式整体剪切破坏: 三角压密区,形成连续滑动面,两侧挤出并隆起,有明显的两个拐点。 浅基下密砂硬土坚实地基。
(b)地基破坏的模式局部剪切破坏:基础下塑性区到地基某一范围,滑动面不延伸到地面,基础两侧地面微微隆起,没有出现明显的裂缝。常发生于中等密实砂土中。
(c)地基破坏的模式刺入剪切破坏(冲剪破坏):基础下土层发生压缩变形,基础下沉,当荷载继续增加,附近土体发生竖向剪切破坏。
有整体剪切破坏,局部剪切破坏和冲剪破坏.
地基破坏形式主要与地基土的性质尤其是压实性有关,一般而言,对于坚实或密实的土具有较低的压缩性,通常呈现整体剪切破坏.对于软弱黏土或松沙地基具有中高压缩性,常常呈现局部剪切破坏或冲剪破坏.
基坑失稳是指由于基坑施工时对某些关键部位和工艺如锚索成孔、注浆、张拉以及泄水孔的控制不严引发基坑施工造成事故或达不到设计标准。 基坑施工时,对锚杆锚索土钉的长度、支护桩桩长、喷射混凝土厚度、钢筋网片的连接等方面一般能够进行有效控制和检测,因此对锚杆锚索泥浆浓度的控制、注浆的及时性、预应力的准确施加、自由段的处理、泄水孔的设置显得尤为重要,必须严格按要求施工,方可有效保证基坑安全。基坑帷幕应根据周边的情况及地质条件进行设置,确保合理、经济。
伴随着我国改革开发以来经济的高速发展,城镇化也加快了脚步,众多的人口涌入城镇,低层建筑以其容量小、地上地下空间没有充分利用而无法满足人们日益增长的需求;一般的路面公共交通因其破坏坏境、噪声和振动的影响而很难让人接受。为解决城镇化带来的住房难、交通难等问题,建筑业也发生了巨大变革,城市高层建筑不断涌现,而且向着更高、更复杂的趋势发展;对于交通发展高效地下有轨公共交通,形成四通八达的地下交通网已成为出现在各大城市的规划蓝图上[1]。无论是高层建筑还是地下交通系统都涉及到一个重要的问题,那就是基坑。大大小小由于基坑失稳造成的事故出现在各大新闻媒体上,轻则财产损失,重则人身伤害,一起起建筑事故敲响了警钟,给了我们警示,让我们不得不重视起基坑基坑稳定性对建筑的影响。
在基坑开挖中,影响其安全的因数众多。内因有土壤类别、土湿化程度、支护施工、开挖速率等,外因有气候、临近建筑、坡度、坑壁形式、地表水等,其中开挖速率可操作性较大,合理的开挖速率可以保证基坑的稳定性,同时充分发挥人、材、机等作用。所以研究开挖速率对基坑稳定性的意义重大。
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