Failure of Shallow Foundation & Preventive Measures

基础失败的主要原因如下

1. Unequal settlement of sub soil
2. 砌体的不平等定居点
3. Presence of expansive soil below foundation
4. Presence of mature trees
5. Seasonal changes

1。亚地区不平等

这是基础失败的最重要原因之一。不平等的解决导致基础的裂缝，并最终导致整个结构的失败。

Unequal settlement of the foundation generally occurs for the following reasons

• 在整个地点，亚地区可能不统一。这意味着如果该地点的某些部分由可压缩的土壤（例如粘土）组成，而某些部分由硬地层（例如岩石）组成。
• 来自结构的负载可能不统一
• It may occur also on building constructed on sloping ground.

补救措施

• 基础应以这样的方式设计，以使结构的不同部分的土壤压力和相应的差分沉降减少到最低。
• 从上层结构的负载应在土壤安全轴承能力的范围内。
• 基础should be constructed with right type of material to avoid disintegration of foundation due to presence of harmful chemical f of soil or water
• 基础should be so proportioned that center of gravity of load from the structure coincides with the center of gravity of the foundation.

另请阅读：如何提高基础材料的耐用性？

2。Unequal Settlement of Masonry

通常，建筑墙的基础是用砖砌或石工砌体建造的。不同类型的迫击炮用于这些砌体单元的键合。在施工期间，迫击炮未正确设置，如果承受过多的负载，则开始收缩。这种砂浆的收缩可能会导致砌体的不平等定居点，从而导致墙壁上的裂缝。

补救措施

• Workable mortar should be used during construction. Workability of mortar is measure by performing consistency test of mortar. Mortar used in construction should not very lean or very stiff.
• The maximum height of construction for a wall in a day should be limited to 1.5 m.
• Masonry should be cured for at least 10 days. This will help the mortar joints to attain its required strength.

另请阅读：如何确定砖石砂浆的一致性？

另请阅读：Recommended Values of Consistency for Different Work

3。基础以下存在膨胀的土壤

存在膨胀的土壤（例如黑棉土壤）具有随着水分含量变化而显示体积变化的趋势。这些类型的土壤缩小和膨胀过度膨胀，从而导致基础的不同结算。

补救措施

• 黑棉土壤上的最大负载应限制为5吨/m²。如果水有机会与粉底接触，则负载应限制为9吨/m²。
• 基础应放置在裂缝停止延伸的深度。基础的最小深度至少应为1.5 m。
• Try to避免直接接触黑棉土壤与基础材料。这可以通过为粉底板制造更宽的沟渠，并用沙子或莫罗姆（Morroum）填充粉底砌体的两侧。

另请阅读：如何避免在黑色棉土中的基础失败？

4。Seasonal Changes

• In rainy season, a part of the rain water finds its way to move into ground. This water bring with it some form of salt. This salt when come in contact with foundation material causes it to deteriorate.
• 大雨跌落可能导致土壤侵蚀或冲刷，从而影响粉底
• 季节性变化也会改变水位的深度，从而导致膨胀土壤的肿胀和收缩。这可能会导致基础上的裂缝。

补救措施

• 应该选择基础的深度，以至于季节性变化的不利影响被最小化。
• 如果水位有可能提升到基础水平，则提供足够的排水设施。
• Always use dense cement concrete or stone masonry where there is a chance of sulphate attack to foundation.
• 在墙壁表面附近的地面上提供适当的坡度，以使雨水从墙壁流动。

另请阅读：如何计算浅水基础的深度？

另请阅读：How to Protect Concrete from Sulphate Attack?

5.Presence of Mature Trees

Where clay soils contain trees the problem is more severe. Trees and heavy vegetation draw a considerable amount of water from the ground during the growing season. A mature poplar takes up as much as 1000 litres of water per week. In long hot summers with little or no rainfall the tree will continue to draw moisture out of the ground and the clay will shrink. This, of course, is in addition to the seasonal drying mentioned above. If buildings are sited near individual or groups of trees serious cracking in the walls can occur as a result of ground movement.

树了粘土土壤在哪里opposite problem occurs. As the ground slowly regains moisture it will expand and this can continue for a period of up to 10 years. The pressure that dry clay develops when reabsorbing moisture is likely to be greater than that imposed by the building load and upward movement of the structure will occur. If houses are built on the site before this ground expansion is complete, cracking will occur in the walls and foundations; the swelling will be uneven because it will be concentrated around the removed tree.

补救措施

• 为了防止这种运动影响带状地基，它们必须比树根更深。当然，另一种选择是将建筑物远离树木。
• It is considered reasonable to keep the foundation at least the height (H) of the tree away from a mature single tree and about 0.5H from rows of trees.
• 对于成熟的树木，最小安全的距离应优选15 m，对于幼树，应适当增加距离。