Type of Foundation Depending On the Ground Conditions - Assignment Example

Part (c) The ground conditions in the area where this house is to be built are of firm clay underlain by chalk at a depth of approximately 1m below ground level. Explain why a trench fill foundation would be appropriate in this location. Answer: There are two soil conditions being provided in the problem, firstly it is the firm clay and secondly it is underlain by chalk, both the soil types possess different properties and therefore any foundation that is to be suggested should counter the problems associated with them.

The problem with the chalk is that it is highly porous and its structure contains excessive voids in it. Hence there is a high possibility of water transmission through chalk layers. Incase the water table rises there will be no obstruction offered by chalk therefore it will reach the foundation level and eventually enter the structure; this is why we are using trench fill, as we know concrete is a compact and non porous material it will give water and damp proofing to the foundation and walls as well as structural stability as well and eventually there is very less settlement.

The other reason for the trench fill foundation is the presence of clay which has expansive and swelling properties when water enters it, due to this property when ever the clay comes in interaction of water it bulges and swell hence produces an uplift pressure which results into a danger of differential and localized movement of foundation which leads to stresses and instability in the structure. This problem is largely minimized with trench fill footing in which reinforced concrete component counteracts the uplift force hence no settlement is seen.

Then another rationale which makes the choice of trench fill detrimental is the foundation depth restriction which is made by the chalk layer at 1m depth and as a result now we can not go to greater depths for foundations and have to select a foundation that sustains the load within this 1 m, in that case we are left with no other solution but to select trench fill foundation. Part (d) In a different part of the site the ground conditions are very different with soil of poor and uneven bearing capacity.

What type of foundation should be used in this location; explain your selection. Answer: Now the problem in this situation is the soils weak bearing capacity and less strength to sustain loads without letting them penetrate or move. There are two solutions to this problem one is to change the soil in that area with a suitable soil but that is not going to be the option here. On the other hand another solution to the problem can be to some how reduce the load on the soil so that it can support the structure and for that reduction in the load we are going to use a different type of foundation which would be the Mat foundation.

This selection is made because the mat foundation enables us to spread the load over the whole building area reducing the load per unit area and hence lessening the chances of localized failures of soil as it might fail in the areas where the soil is weak resulting into differential settlement. As a matter of fact we need to have a structural stiffness and integrity in the structure and for that we should not have differential or localized failures of soil, which will happen in the soil condition of our site as it has uneven bearing capacity.

In order to eliminate this problem and to safeguard the integrity of structure we use Mat foundation because in this the foundation acts a one uniform body that floats and apply equally distributed load over the ground surface hence eliminating the possibility of relative movement of structural and foundational components. The other option to solve the very same problem is pile foundation, but mat foundation is given preference because pile foundation requires more money, mobilization of machinery, manpower and soil testing before its application.

So in the end we are only left with Mat foundation which gives more stability and safety as compared to strip footing and gives more economy as compared to pile foundation. References 1. P.N Khana (2007). Practical Civil Engineering Handbook. 5th ed. India: -. Ch 7, Pg 10-20. 2. Trench Fill Conservatory Foundations. Available: http://www.conservatoryquoteonline.com/Trench_Fill_Foundation.asp. Last accessed 17-02-2011 3. P. W. McDowell. (2005). Detection of clay filled sink-holes in the chalk by geophysical methods.

Available: http://qjegh.geoscienceworld.org/cgi/content/abstract/8/4/303. Last accessed 16-02-2011. 4. Blackwell Publishing (2004). Groundwork and Foundations. Available: www.blackwellpublishing.com/content/BPL./BY032-03_p37-80.pdf. Last accessed 17-02-2011. 5. University of the West of England, Bristol. (2006). Foundations. Available: https://environment7.uwe.ac.uk/resources/constructionsample/cd_hybrid_mini/topic_foundations/foundationtest.pdf. Last accessed 17-02-2011