Question

State five problems that may happen during design, construction and operation of shallow foundations. Then, discuss simple solution for each.

Answer 1

If the width of a foundation is greater than it's depth then it is said to be shallow foundation ,usually thsese type of foundation found in the building construction. In case of shallow foundation the common problem faced during design,construction and operation may be as follows-

1-Non uniform soil strata

The shallow foundations have a low depth that is why the major role played by the soil ,and soil must be capable to bear the load of super structure.If the soil strata are in such a way that it is not categorised in any type of soil and type of soil even changes in the foundation at different point.So in these scenarios it is difficult for designer to design a shallow foundation and at the same point of time this is the problem which also faced during construction.

Solution- If the problem is as above then there may be two solution first is excavation till the solid strata which would be capable in bearing the load and second solution is soil Improvement by adopting the different method of soil improvement such as calcium corbonate method,use of cement bag,vibrofloatation,sand column etc.

2-Shallow foundation at slope

Since the depth of shallow foundation is not much so that it create difficulty in design when it has to design on slope simultaneously it also creat problem when has to construct at slope.

Solution- If the slop is high where the shallow foundation has to construct then either filling or cutting may be done to reduce the slope .Here in this case also cutting is prefered because filling of soil can not be fully compacted eaisly and filling soil get settle till many year.

3-Soil erosion near shallow foundation

If the soil erosion is much prevelent in region of shallow foundation then designer have to think about to increase the durability and serviceability .The cause of soil erosion may be the high rainfall,high wind velocity or drainage around the shallow foundation.High rain fall ,high wind pressure and drainage will always affect a construction site badly and will creat a problem in construction.

Solution- To protect the foundation from the diverse impact of erosion ,the designer is advised to change the material used or change the grade of material .In case of erosion area, concrete should be of high grade and cement used in the concrete should be water phobic in nature.And the most importantly the surrounding area of the shallow foundation should also be improved even by pcc(plain cement concrete).

4-Water table at lower depth

It the water table is at lower depth ,then in the rainy season the depth can be reduced and can also be reach till the shallow foundation or near the shallow foundation this will lead to collapse of the structure.The gap between water table and shallow foundation can also be reduced of there is seepage of water because of presence of water body in the surrounding area.The water table at lower depth creat problem in construction when exacavation is practiced for to get a hard solid strata.

Solution- As such there is not any proper solution if the water table is at very low depth. As discussed above in case of the low depth of water the designer can change it location or can change its type of foundation from shallow to deep.But if the case is not much severe designer is adivesed to soil improvement and the width /cross section of the shallow foundation increase as much as possible .

5-When the conjugated area

As we all know that the width of shallow foundation is broader ,so it requires much area for the construction .And it becomes very difficult if there is physical hindrence or populus area .These are the also the area of consideration for the designer even it creat more difficulty in construction.

Solution- The solution for designer is to reduce width by increasing the depth and standard material and advice for the construction engineer is ,that engage only the those area for construction which can be completly constructed in very few time or days.