I. Forms of cracking and damage of buildings
1) Vertical cracks generally appear in the middle of the wall, with the upper width and the lower width being narrow, as shown in figure 1.
2) Oblique cracks are most common in corners, gables, and front and rear and indoor partitions, as shown in Figures 2 and 3.
3) Inverted splay crack, and corner crack develops to form inverted splay, as shown in Figures 4 and 5.
4) Horizontal fracture of independent brick columns is more common in brick columns of verandah, as shown in Figure 6.
5) Ground fissures, when ground fissures pass through buildings, oblique cracks and vertical cracks are produced, as shown in Figure 7.
II. Changes in cracking and damage of buildings
The expansion and contraction deformation of expansive soil foundation is mainly affected by climate change. Climate has a seasonal cycle and a period of several years. Cracks change with the change of climate cycle, which is the easiest to identify. Cracks in buildings usually appear after 3 ~ 6 years of construction, because the amount of repeated deformation with the climate needs a process, that is, the transfer and accumulation of water need a process to make it expand.
Thirdly, the aggregation of cracks and damages in buildings.
The damage of buildings on expansive soil foundation is mainly affected by climate, and the climate zone changes greatly, which is basically the same in a county or city. Therefore, as long as there is a certain range of expansive soil distribution, the aggregation of building cracking and damage is inevitable. For example, in Maoming area, not only the architectural cracks in a village appear in groups, but also the villages with architectural cracks in groups appear in groups. Within the scope of 200km2, there are groups of cracks in buildings in 45 villages.
Four. conclusion
Judging whether a certain soil is expansive soil is the premise of preventing geological disasters of expansive soil. Although there is no internationally recognized standard for judging expansive soil, it is generally believed that many buildings are cracked and destroyed due to the expansion and contraction of expansive soil, and expansive soil does exist in many parts of the world. Therefore, it is of great significance to report and summarize the characteristics of building cracking and damage caused by expansive soil, and use these characteristics to judge the distribution and nature of expansion.
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(This article was originally published in the exhibition board area of the 30th World Geological Congress)