soil in construction7

DG

1. Should contractors be included in foundation design decisions?

    Yes, I believe contractors should be knowledgeable in the design. When the architect/engineer designs the structure, just having sit in the design process (as we’ve students getting all parties involved to collaborate), the contractor may have a better idea on how to approach the project and whether or not he/she wants to bid on it.

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2. How much can foundations for a high-rise building move?

High-rise buildings have presented many challenges to engineers, especially in relation to structural and geotechnical design. Many traditional methods cannot be applied with these structures and therefore, engineers have to employ state-of-the art methods. Soil and rock parameters adopted for design should consider the ground conditions. High-rise buildings have a seismic performance criteria where they are involved with lateral resistance: wind, earthquakes. The natural period of the building in relation to the period of seismic waves that can be expected has forces of .100 to .200 g. The tilting of a high rise building is smaller than ½000, while the maximum of the building is up to 2.8 cm.

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3. Can errors occur in preparing soil reports?

Yes, errors can occur on soil reports. If they do, chances are they could have been caused by the variation samples. There could also be discrepancies on how the samples were handled. This could include how the samples were transported.

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S P

2. How much can foundations for a high rise building move?

As mentioned in chapter 11 reading,  deep foundations serve to by-pass unsatisfactory soils and transfer the building loads to a suitable bearing stratum. Because of the many variables and uncertainties, building foundations can be have a deflection ranging from 1-2 inches with out concern.  Of course there are still several other factors such as soils, lateral wind forces etc.

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3. Can errors occur in preparing soil reports?

Absolutely, geological technical (Geo-Tech) sampling reports often occur in the following areas: data handling, deviating from the sampling methods, transport of the soil samples, sample room temperatures , and misreading the data collected are some of the concerns that may occur.  

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4. How much safety factor should be applied to foundation design?

To begin with, understanding how to apply a "Factor of Safety" (FoS), is defined to be the Ratio of the allowable stress to the actual stress.  Depending on several factors in foundation design, the FoS can vary between not less than 1and not greater than 3 in some instances.  For instance, a FoS of less than 1, is more than likely that the foundation will fail.  This means that you are not taking into account any of the potential soils conditions, water table levels, moister of soils, structure type methods etc.  High rise foundations may exert a FoS between 2-4 vs a shallow foundation may exert a FoS between 2-5.  A final note that a SoF greater than 1, represent the allowable stress is within the allowable limits before failure.   

Factor of Safety (F) = actual load stress / ultimate load stress

References:

https://www.hindawi.com/journals/mpe/2017/3043571/

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M O

1. Should contractors be included in foundation design decisions?

My initial answer is no. However, I have been on projects where the contract is design-assist or design-build where the contractors’ assistance is needed and this has included foundation design decisions. Contractors have also been brought in because of the expertise to help on permanent and temporary excavation controls as well.

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2. How much can foundations for a high rise building move?

How much a foundation for a high rise can move varies on the structures. There is an allowable movement of 1-2” which seems customary to expect however anymore amount has to be determined based on the factors of design- soils, existing conditions, and design of the structure. The water table can also have an effect overall which may be a factor in movement.

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3. Can errors occur in preparing soil reports?

Errors can occur because there is always the chance of human error involved in sampling, transporting, testing, and reporting. However, with a chance of risk having a detrimental affect on design, any errors should be avoided by proper supervision of every process in creating the soils report.

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