Question

Write an essay 500-600 words about

“Causes of Failure in Soils”

You should critically discuss; what a geotechnical engineer care about to avoid failure, what should be tested-measured-monitored, and give examples of necessary analyses and judgments.

You can create a concept map to help you in structuring the essay!

You must not directly copy and paste from the references. You have to write the essay by your own words as a summary of what you understand.

Write an essay 500-600 words about

“Causes of Failure in Soils”

You should critically discuss; what a geotechnical engineer care about to avoid failure, what should be tested-measured-monitored, and give examples of necessary analyses and judgments.

You can create a concept map to help you in structuring the essay!

You must not directly copy and paste from the references. You have to write the essay by your own words as a summary of what you understand.

Answer 1

Causes of failure in soils

Main reasons for soil failure are
  
1. shear failure: when applied load on soil subsurface (in case of shallow foundation) or when applied through friction (in case of friction pile) is beyond the limit of load which can be applied on soil safely.
Shear properties of soil can be improved by various methods such as compaction of soil, adding additives having cementous properties, use of advance methods such as geotextiles and geomembranes.

  
2. differential settlement: When a structure in constructed on a levelled surface, if one part settles more than another, it leads to development of stresses which might not be included in design and cracks, which can eventually lead to failure of structure.

3. settlement beyond permissible limit: Code puts a limit on allowed settlement after construction of a structure, so its role of a geotechnical engineer to prevent settlement beyond this limit.

4. shrinkage and expansion: When water drains in and out of expansive soil, it expands and shrinks respectively, which is very dangerous as it can lead to large amount of settlement or differential settlement, which puts structure at risk of collapse or cracks.
As a geotechnical engineer, soil must be tested for its expansive properties and if exist proper treatment with lime or cement should be done to make soil suitable for construction over it.

5. presence of vegetation: if any vegetation is present in site of construction, it should be cleared and made sure that there is no subsurface organic matter present , because organic matter such as vegetation decomposes with time and space which was occupied by this matter is left as void in soil which will finally lead to unequal settlement of soil, which will eventually result in structure failure.  

6. presence of nearby mature trees: As a result of trees photosynthesis they use water from nearby soil, if water below a foundation is used by a tree, it will lead the soil to settle and thus the failure of strucure is possible.

Role of geotechnical engineer is proper selection of site of construction keeping all the challenges in mind and if its solution is possible and economically feasible or not. After site selection his role is to decide the soil treatment if required and design the foundation depending on soil type and load requirements. He also needs to prevent soil failure by proper analysis of soil properties where construction needs to be done by keeping drainage and submerging conditions in mind.
Proper compaction of soil to prevent excessive settlement post construction
Proper selection of foundation type and its design depending on type of soil strata and its load bearing properties.
Necessary treatment of expansive soil by using Cementous material such as lime or cement itself if feasible before construction to reduce expansive property.
Scraping of top layer of soil if vegetation is found in or in the soil.

Soil should be tested in lab for its properties discussed above and made sure that construction is being done as per the design parameters. Also, it is to be made sure that quality control measures are taken care of while construction is going on site.