The soil compaction is an important subject of soil mechanics or Geotech engineering. Soil being the most important component of construction, it is necessary to determine and alter the present condition of soil for the purpose. In general words, soil compaction is the process of densification of soil, which involves the expulsion of water content from between the particles so as to attain the adequate strength. Soil Consolidation basically involves the expulsion of water without replacement of air content. Soil compaction is a process that also involves consolidation. But in actual consolidation is different from compaction if we study the roots.
The basic difference or criteria that dissimilar these terms is that, in compaction there is involvement of external or applied forces or loads that contracts the free spaces between the particles and reduces the volume. Whereas in consolidation is the densification or volume reduction without the involvement of external applied load. Since the compaction is the process of volume reduction and densification, so it can be attained naturally or by man-made mechanical techniques. The natural method does not involve the interference of machineries as it gets compacted due to the movement of animals and other living bodies, and internal suction of soil (evaporation of water content from between the soil particles).
Importance of soil compaction in construction industry
The characteristics of soil on earth surface varies with the varying terrain and geographical condition. Thus the property of soil does changes with the changing of places. The soil of a given place may not justify the entire required standard to withstand for a particular constructional purpose due to various reasons, but it can be altered by opting some methods or processes. In general, the pre selected soil for a construction should have adequate strength, be relatively in-compressible so that future settlement of soil is not significant, be stable against volume change as water content or other factors vary, a durable and safe against deterioration and possess proper permeability. The soil beneath the foundation of a building, road and pavement, dam, hydro project and under-ground tunnels is compacted before actually erecting the structure.
Different methods for determination of adequate compaction
The in-situ density of the soil is the major criteria for determining the soil compaction. Generally the in-situ density of the soil is first determined and then it is compared with the laboratory readings. The main aim of these methods is to determine the optimum water content at which the soil attains the maximum density. The various tests which are under taken to determine the adequate compaction of soil are as follows:
- Standard Proctor Compaction Test
- Harvard Miniature Compaction Test
- Abbot Compaction Test
- Jodhpur Mini Compaction Test
Among all the above mentioned tests the Proctor test is the most widely used test. The Proctor test has two types, one is standard Proctor and other is the Modified Proctor test. The Standard Proctor and Modified proctor tests are known as light and heavy compaction tests respectively. As mentioned earlier the standard compaction test is the most common method for determining compaction but the heavy compaction is needed for heavier transport and military aircraft. The Modified Proctor test was developed to give a higher standard of compaction.
Different methods of soil compaction
There are various methods of soil compaction for achieving the adequate limits and standards that would suit the purpose. Although there are various methods but they has their own suitability. Some of the most significant techniques that are used in compaction are as follows:
1. Static method – In this method an amount of stress is slowly applied to the soil and released.
2. Impact method – As the name suggests, the impact method is related to impact stress. It is carried out by dropping a heavy mass of object on the surface of interest.
3. Vibration method – The vibration method generally deals with the application of vibrating stress on the soil mass. It is the repeated application of stress via a mechanically driven plate or hammer which compels the soil particles to rearrange in a new formation that have greater density and lesser grain to grain space.
4. Gyration method – It is a method that is very much confined to laboratory. In this method a static stress is applied and maintained in one direction while the soil is subjected to a gyratory motion about the axis of static loading.
5. Rolling method – In this method a mass of cylindrical mass is rolled over the soil mass. Although the result of method is largely depends upon the situation of soil and amount of applied rolling load.
6. Kneading method – Here the shear stress is applied by alternating the movement in adjacent position which leads to compaction of soil.
Therefore the soil compaction can be done by using any one of the above method according to the needs and requirements. The negligence of this Meta aspect can also lead to failure of structure that is why the Geotech engineering is an important branch of civil engineering.