诱使沉降法纠正偏移建筑的模型试验及案例分析

 中国西北地区大部分土质为湿陷性黄土，这些地区修建的多层建(构)筑物中，有些由于地下管线漏水、室外排水措施不当等原因，造成地基土发生不均匀沉降，使建(构)筑物出现倾斜等工程事故。为使这些上部结构完好，保证基础存在不均匀沉降的建(构)筑物的安全和正常使用，应使其倾斜得到纠正。通过工程实践和模型试验，提出一种将水注入建筑基础下土体诱使地基补偿沉降纠正偏移建筑的方法。对一个放置在与工程现场相似、人工处理的湿陷性黄土基础上的建筑模型进行纠偏试验。该模型相似比取1∶5，高度为3 m。采用诱使沉降法，首先在建筑一侧开沟，释放侧向约束应力，其次在沟底向建筑基础下部掏水平圆孔，减小地基承压面积，增加地基土的竖向应力，然后向水平孔注水软化地基土，诱使建筑基础产生沉降，达到纠偏的目的。纠偏模型试验测试得出以下结论：(1) 应力释放和地基应力增加产生的水平位移和沉降仅为注水软化地基的1%～2%；(2) III级自重湿陷性黄土基础在压力作用下，其初始湿陷含水量为12%，但当含水量达到25%时，湿陷沉降明显加速，因此，采用注水诱使湿陷沉降纠偏时控制湿陷含水量为20%～30%，持续2～3 h/d，可使纠偏过程安全且效果良好。工程案例和按照试验方法进行的大量工程纠偏实践证明，此方法可用于湿陷性黄土地区的纠偏实践。

MODEL TEST ON RECTIFICATION OF INCLINED BUILDINGS BY INDUCED SETTLEMENT METHOD AND CASE STUDIES

Collapsible loess is widely distributed in Northwest China，where a lot of buildings are founded on shallow foundations. Improper ground treatment，underground water pipe leakage or rainwater infiltration have caused many of these foundations to suffer from differential settlements leading to inclination of buildings. Such inclination not only causes problems in the building foundation but also is hazardous to inhabit in some cases. Through model tests and field practice，a method injecting water to the foundation soil has been given to induce compensating settlement to rectify the inclination. The model tests in laboratory are conducted on the model buildings，which are 3 m high and placed on reconstituted loess compacted to the same void ratio in the field. In the first stage，a trench parallel to one side of the building is dug and side holes perpendicular to the trench are drilled underneath the building. This allows stress leading to settlement relieved. Then water is injected to the foundation soil through the trench for observation of settlement due to soil softening by the injected water. In the second stage，the same procedure is repeated to the foundation on the opposite side of the building. The following results can be drawn by the model test. (1) The settlement and horizontal displacement due to the stress release and increase of foundation stress amount to about 1%–2% of those due to softening by the injected water. (2) Settlement begins to take place when the water content reaches to 12% for the collapsible loess with category III in Lanzhou. When the water content is 25%，the settlement velocity increases obviously. Therefore，the water content of the softened soil should be controlled between 25% and 35% for about 2–3 hours one day. The case study and many projects for rectifying inclined buildings illustrate that the proposed method can be used to rectify the inclined buildings in loess region.