The process of consolidation
Consolidation is compressing soil by applying a force. The result is that volume decreases. The decrease in volume occurs because air and water is expelled from the voids of the soil thus reducing the pores.
There are two types of consolidation (1) Primary consolidation and (2) Secondary consolidation. In this paper, these two forms of consolidation process will be described. Soil samples were collected and consolidated over time.
Primary consolidation
This consolidation occurs when all water from the soil is expelled by application of a force. Volume of the soil is reduces in the process. The expulsion of water from the voids in the soil will depend on the permeability of the soil (Attaulah, 2012). Therefore, this process is dependent on time.
Secondary consolidation
After squeezing all water from the voids of the soil, further compression to reduce the volume of the soil is called secondary consolidation. Further decrease in volume occurs as a result plastic deformation of the particles of soil (John, 2011). If the soil particles are large, they may crash into finer particles thus reducing the volume they occupy.
Hazards of soil consolidation
Consolidating soils can be hazardous. Adding large amounts of compacted fill puts a substantial load on the soil and can result in significant settlements. An example of this is New Jersey Meadowlands (Swan, 2006). This complex was built in the 80’s on the marshlands of river Hackensack. The negative effects observed due to placement of compacted fill were settlement of soil as follows:
- 0.25m settlement that occurred during filling
- 0.12m settlement during construction
- 0.10m settlement in the next 10 years
6.0 Discussion of results
The results showed that, with time, pressure acting on a wet soil sample caused reduction in volume of the sample. The soil sample had loam soil characteristics; it was both fairly porous and medium soil particles. The particles were soft too. It was observed that at the beginning of the experiment, when a compressive force was applied to the soil, there was no observable difference in the volume. This implies that there was no instantaneous compression. After about 80 minutes, the results obtained showed a constant volume tendency. It was deducted that, at this point, all water had been expelled from the soil and any other compression would be secondary.
The implications of these results are that water can be easily expelled from the soil hence the soil cannot have extremely detrimental effect on a structure being set on it. However, the time taken to drain water from the soil can be reduced by treating the soil. Sand could be added to this soil to make it more porous thus easily releasing water under pressure (Whitlow, 2000).
Lime could also be used to treat the soil to make it ready for construction of structures such as roads and pavements (National Lime Association, 2004). Lime treated soil becomes easier to compact and quickly drains water away. The property of lime that is utilized in soil treatment is that it reacts with water. Lime dries the soil faster than it would be if the soil was to dry naturally.
Protection for a site being consolidated
If the site being consolidated has loose soil, the site could be secured by sinking a concrete fence to avoid settlement during consolidation. Fencing to avoid human and animal interference is also handy.
Experimental errors
Consolidation results are dependent on factors like: type of loading (continuous or rapid), boundary impedance, effect of temperature and ring friction of the consolidating device. Temperature could cause the ring to expand during the experiment hence lowering its friction. This effect is un-accounted for in the results hence a source of error. Varying the ring friction causes variation in consolidation pressure hence a continuous load could behave rapid in some instances thus resulting in error (Shan, 2009).
References
Attaulah, S. (2012). Soil consolidation. Accessed on 24-Feb-2012, from http://scetcivil.weebly.com/uploads/5/3/9/5/5395830/lec-6.soil_consolidation_compatibility_mode.pdf
Reddy, K. (2009). Engineering properties of soil based on lab test. Accessed on 24-Feb-2012, from http://www.uic.edu/classes/cemm/cemmlab/Experiment%2011-Consolidation.pdf
John, B. (2011). Settlement and consolidation. Soil mechanics. Accessed on 24-Feb-2012, from http://www.gramme.be/unite9/geotechnique/SoilMech_Ch4_Settlement_and_consolidation.pdf
National Lime Association. (2004). Lime stabilization and lime modification. Lime treated soil construction manual. . Accessed on 24-Feb-2012, from http://www.graymont.com/technical/Lime_Treated_Soil_Construction_Manual.pdf
Whitlow, R. (2000). Basis soil mechanics. 4th ed. London, UK: Prentice Hall.
Swan, C. (2006). Foundations on Weak and/or Compressible Soils. Accessed on 24-Feb-2012, from http://www.engineering.uiowa.edu/~swan/courses/53139/notes/weak_compressible_soils.pdf
Shan, H. (2008). Consolidation test on soils. Accessed on 24-Feb-2012, from http://www.cv.nctu.edu.tw/~wwwadm/chinese/teacher/Ppt-pdf/AGTwk5Consolidation1.pdf
