Question

1. Please give concise and precise answers for the following questions. Your answers should be no more than five (5) sentences. a) What is consolidation (5 points)? b) Is consolidation the only reason why soil layers having settlements (5 points)? c) Under what kind(s) of condition will soil layers consolidate (5 points)? d) What are the basic assumptions of Terzaghi’s consolidation theory (5 points)? e) Based on the consolidation theory proposed by Karl Terzaghi, which factor from the results of a consolidation test does control the quantity of consolidation process (5 points)? f) Based on the consolidation theory proposed by Karl Terzaghi, which factor from the results of a consolidation test does control the speed of consolidation process (5 points)?

Answer 1

(a) Consolidation is the gradual reduction in the volume of a partly or fully saturated soil under sustained loading and is mainly due to the expulsion of water from the soil pores. When a static load is applied to a saturated (or nearly saturated) soil, It is first carried by the pore water because the structure must compress to take the load. There is a sudden increase in the pore water pressure, called the ‘excess pore pressure’ and its initial value v0 is equal to the total, applied external pressure. This build-up of excess pore pressure causes the water to drain out of the pores, allows the soil to consolidate.

(b) No, consolidation is not the only process causing settlement of soil. Other process include  
1. Structural collapse of soil
2. Mining subsidence
3. Underground erosion
4. Change in the vicinity
5. Thermal change
6. Landslides
7. Frost heave
8. Creep
9. Vibration and Shocks

(c) under vertical stres consolidation takes place. These stresses can be caused by lowering in ground water table, dessication, loads due to structure, self weight of recently placed soils.

(d) Basic assumptiins in terzaghis consolidation theory are
1. compression and flow are one dimenional.
2. Darcys law is valid
3. Soil is homogenous and fully saturated.
4.Soil grains and water are incompressible.
5. Strains are small and there is a unique relationship , independent of time between void ratio and effective stress.