Flashcards
Consolidation and 1D settlement
Cards in this deck (9)
- 1What are the three sections on a typical load-settlement graph?1. Initally high rate of settlement and high excess U. Undrained behaviour.
2. Transient behaviour. Settlement rate reduces with time.
3.Drained behaviour. - 2Why can soil consolidation not fully be compared with analogies?Drop in head is not uniform in soil during consolidation as it depends on the position relative to the drainage points. Hence consolidation and resulting compression of the soil at different stages in time and excess pore pressure in not unifomr throughout the sample. Rate of consolidation is not constant, faster at the beginning and tapering off at the end. Consolidation time also depends on the drainage path.
- 3What is an isochrone?A line representing the distribution of excess pore pressure within an oedometer sample at a given time after loading .
- 4What are the properties of an isochrone?1. The slope if the isochrone at any point is proportional to the magnitude of the hydraulic gradient.
2. The overall compression measured at the surface of the sample and a given consolidation time is equal to 1/E'0 times the area swept out by the curve. - 5What are the assumptions made in consoliation?1. Soil is homogeneous
2. Soil is fully saturated
3. Solid particles and water are incompressible
4. Compression and flow are on dimensional occurring in the vertical direction only
5.Strains are small
6. Darcy's law is valid at all hydraulic gradients
7. Coefficient of permeability is constant
8. Coefficient of volume compressibility is constant
9. Load is applied instantaneously and remains constant thereafter - 6What are sand drains?Sand drains are holes bored in clay and filled with sand. Loading of clay results in vertical compression, due to simultaneous vertical and radial flow of water. Sand drains reduce the drainage path and so lead to accelerated consolidation.
- 7Why could lab tests give unreliable permeabilities?In the lab, flow is usually vertical and Cv is therefore based on Kv. Therefore, settlement in the field could be quicker than predicted if the soil has greater horizontal permeability than verical permeability.
- 8Apart from sand drains, give 2 other ways of accelerating consolidation.Geotextile drains: Alternative to sand drains. A corrugated plastic core provides rapid drainage. Geotextile filter material warps around the core to preventing cloggin of the core by fines.
Preloading: Clays may be preloaded with a surcharge fill which is maintained in place until consolidation settlement equals that which would result under application of teh final building pressure. - 9What 4 things reduce the time for consolidation?1. Reducing the footing area
2. Using circular/rectangular loaded areas rather than strip footings
3. Increasing horizontal permeability
4. making the underside of the foundation permeable.
Information
- Description
- Geotechnical Engineering Flashcards on Consolidation and 1D settlement, created by Billie Santos on 04/03/2017.
- Created by
- Billie Santos · Mar 2017
- Updated
- Mar 4, 2017
- Views
- 0
- Rating
More on Consolidation and Settlement