The security and dependability of the extra long bridge structure have become the general concern question of the society in these days . because of the influence of the prestressed loss , the real stress does n ' t coincide with the designed stress , that is to say , the calculated stress does n ' t display the condition of the real structure stress properly , and thereby the undiscovered danger leads to the quality of the engineering construction 特大型桥梁的结构安全可靠性已成为当今社会普遍关注的问题。对大跨度预应力混凝土桥梁而言，由于预应力损失的影响，结构的实际应力与设计应力很难完全吻合，即计算应力不能很好地反映结构的实际应力状态，从而留下安全隐患，严重影响了工程建设质量。
It is essential to study collapsibility and influential factors of loess , evaluate correctly collapsible grade of loess , find out appropriate prevention and cure countermeasure in order to improve construction quality of road , alleviate or eliminate diseases of road results from collapsibility of loess , guide design and construction of road in guanzhong area 为了提高公路建设质量，减轻或消除因黄土湿陷而造成的公路病害，以便指导关中地区公路的设计和施工，很有必要对黄土湿陷的特性和影响因素进行研究，准确评价黄土的湿陷等级，找出合适的防治对策。
( 2 ) based on the real condition of urban human settlements construction in lanzhou , the dissertation draws a conclusion that the main factors which influence the urban human settlements in lanzhou is natural subsystem , according to the identical characteristic of the trend of the natural subsystem and the urban synthesis construction quality ( 2 )结合兰州城市人居环境建设的实际，根据综合建设质量走势图与自然子系统建设走势图的波动周期较为吻合特点，得出了影响兰州城市人居环境的主要因素是自然子系统的结论。
