Geotech Exam 3

If a site consisting of a thick clay deposit has seasonal fluctuations in the depth to the groundwater table (deeper groundwater table in the summer, shallower groundwater in the winter), would the overconsolidation ratio be greater in summer or in winter?  Why?

Higher in winter because higher water table will decrease the effective stress

What are the three main components of settlement in soils?

1) Immediate - settlement occurs very quickly after loading

2) Consolidation - Time dependant settlement occuring as water squeezes out of the soil

3) Secondary camp - Longterm settlement occuring at a constant effective stress

Which of the following soils would you expect to undergo the most settlement during consolidation:

SC, CL-ML, MH, GM

MH - higher plasticity means higher consolidation

Explain the process of consolidation in your own words

Time dependant squeezing of water out of the soil due to external loading

How does a flucuating groundwater table lead to overconsolidation

When water table rises the soil will become overconsolidated because it will remember stress

Which of the following mechanisms is not a possible cause of oversonsolidation

Soil erosion

Structure Removal

Embankment construction

Excavation

Embankment Construction - addes soil

Which of the following is not one of the three main sources of settlement in soils?

Creep

Heave

Secondary Compression

Consolidation

Heave

Explain how a geotechnical engineer uses a Mohrs Circle

Find stress on a plane and how it will fail

Which values can be obtained from a Mohrs Circle

Principal Stress

Max shear stress

Horizontal stress

Shear Strain

Principal Stress, Max shear stress, Horizontal stress

Define the critical gradient, and explain how it is calculated.

The hydraulic gradient at which the effective stress becomes zero, causing soil particles to lose contact

(Sat unit weight - water unit weight)/water unit weight

Water flowing through soil exerts __________________ forces, which when large enough can reduce the _________________________________ to zero. This is know as the ___________ condition.

Seepage

Effective Stress

Quick

Which of the following values can you obtain from a flow net? Select all that apply.

Excess pore pressure     

Gradient      

Settlement     

Capillarity    

Total Head    

Elevation Head

Gradient, total head, elevation head

What are the two types of lines on a flow net? Provide a brief (no more than one sentence) description of one of the lines (your choice).

Flow Line

Equipotential lines - lines along which the total heads remains constant