Soil Mechanics and Foundation Engineering Research Department Consultations

Q. What should be done with respect to soil/foundation design in order to construct a building?
A. Perform site investigation and prepare a geotechnical report which should include the followings parameters:

• Type and depth of different soil formations below the building and its classification either cohesive soil (clay), cohesionless soil (sand or gravel) or rock formation.
• Determine the groundwater level.
• Specify the soil condition: saturated, dry, or semi-dry.
• Determine the natural and mechanical soil properties such as: density, water content, cohesion,…etc.
• Determine the allowable soil bearing capacity and compressibility characteristics (settlement) to support the building for all possible loading conditions.

Q. How to determine the soil bearing capacity and settlement characteristics?
A. By performing in-situ tests during the exploration stage in addition to laboratory testing on soil samples recovered from different soil formations below the building. Based upon the tests results, the soil bearing capacity and settlement characteristics can be determined.

Q. How are the soil samples extracted from the site?
A. By executing boreholes either by using manual or mechanical methods and special tools, soil samples can be extracted from different depths. For dry or semi-dry conditions, open pits are usually used to recover the soil samples.

Q. How to specify the type of boring to recover the soil samples?
A. This depends upon the geographical location of the site. The manual method is used for soils located in the delta region and the mechanical method is used for regions which mainly consist of stone or rock formations. Open pits are partially used to extract samples from arid areas.

Q. What are the main considerations to determine the number and depth of borings for a site?
A. The number of boreholes depends upon the area of the building whereas the depth of boring depends upon the height and design loads for the building.

Q. What is the solution if the soil existing at the site cannot support the structure?
A.There is more than one solution to this problem: a specialized engineer can utilize his experience, the acquired information resulting from the site investigation stage, and the economical aspect for the construction in order to recommend the optimum solution for each case.
Examples are:

• Replacing the founding soil with soil replacement layers according to technical specification.
• Using soil improvement techniques.
• Using deep foundation instead of shallow foundation.

Q. What are the types of shallow and deep foundations?
A. Shallow foundations include: isolated, combined, and strip footings in addition to raft foundations. Deep foundations include: piles, piers, and caissons.

Q. What are the types of soil which may be replaced?
A. The most common soils which may be replaced; totally if the layer of soil lasts to a shallow depth or partially if the layer extends to deep layers: weak soft clay, swelling soils, collapsible soils, and in some cases fractured rocks.

Q. What are the types of soil whose characteristics need to be improved?
A. In addition to the above soil types, any other soil which is required to improve its compressibility characteristics as well as to increase its allowable bearing capacity.

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