Soil Compaction Tests

SOIL COMPACTION TESTS

The main differences between the Soil Compaction and the Consolidation process are given below. 

1. Compaction is a process where mechanical pressure is used to compress the soil mass for the purpose of soil improvement. Compaction is a process of increasing soil density and removing air, usually by mechanical means. The size of the individual soil particles does not change, neither is water removed. Purposeful compaction is intended to improve the strength and stiffness of soil. 
2. In the consolidation process, soil volume is reduced by squeezing out pore water from the saturated soil.

TYPES OF COMPACTION:

1. DEEP COMPACTION: Dynamic compaction is a method that is used to increase the density of the soil when certain subsurface constraints make other methods inappropriate. ... The process involves dropping a heavyweight repeatedly on the ground at regularly spaced intervals.
2. SHALLOW COMPACTION: Compaction increases the shear strength of the soil. Compaction reduces the voids ratio making it more difficult for water to flow through the soil. This is important if the soil is being used to retain water such as would be required for an earth dam. 

COMPACTION TEST:

The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density.

STANDARD PROCTOR COMPACTION TEST:

The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density. ... This process is then repeated for various moisture contents and the dry densities are determined for each.
The Optimum Water Content of soil is the water content at which a maximum dry unit weight can be achieved after a given compaction effort. A max dry unit weight would have no voids in the soil. If you were trying to compact a hard dry soil to make it more dense, you might want to get it wet.
Standard Proctor Compaction Testing can be performed in a lab. The testing first determines the maximum density achievable for the soil and uses it as a reference for field testing. It also is effective for testing the effects of moisture on the soil's density.

DEGREE OF SOIL COMPACTION:
CBR TEST:

${\displaystyle CBR\quad }$	= CBR [%]
${\displaystyle p\quad }$	= measured pressure for site soils [N/mm²]
${\displaystyle p_{s}\quad }$	= pressure to achieve equal penetration on standard soil [N/mm²]

STANDARD PENETRATION TEST (SPT): 

SPT is an in-situ dynamic penetration test designed to provide information on the Geotechnical engineering properties of soil.

A widely used soil testing procedure is the Standard Penetration Test (SPT). This test is still used because of its simplicity and low cost. It can provide useful information in very specific types of soil conditions, but is not as accurate as a Cone Penetration Test.

SPT is a common in situ testing method used to determine the Geotechnical engineering properties of subsurface soils. It is a simple and inexpensive test to estimate the relative density of soils and approximate shear strength parameters.

95% compaction means that the soil on the construction site has been compacted to 95% of the maximum density achieved in the lab. ... Compaction is the removal of air voids from soil and to increase the density of soil by bringing particles close to each other.

BEARING CAPACITY:

In Geotechnical engineering, Bearing Capacity is the capacity of soil to support the loads applied to the ground. The bearing capacity of the soil is the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil. Ultimate bearing capacity is the theoretical maximum pressure that can be supported without failure; allowable bearing capacity is the ultimate bearing capacity divided by a factor of safety. Sometimes, on soft soil sites, large settlements may occur under loaded foundations without actual shear failure occurring; in such cases, the allowable bearing capacity is based on the maximum allowable settlement.

Shallow compaction occurs from the surface down to the normal tillage zone. This type of compaction is normally caused by light wheel traffic or animal traffic. Shallow compaction is usually temporary and can be eliminated by normal tillage.

Soil compaction occurs below the surface, so it's hard to spot. The best way to test is to probe the soil with a compaction tester to a depth of 36" to 48". The testing rod should move down through the soil with steady, even pressure, Hard, compacted soils resist penetration with the rod.

The Proctor compaction test is a laboratory Geotechnical testing method used to determine the soil compaction properties, specifically, to determine the optimal water content at which soil can reach its maximum dry density.

To assess the degree of compaction, it is necessary to use the dry unit weight, which is an indicator of compactness of solid soil particles in a given volume. The laboratory testing is meant to establish the maximum dry density that can be attained for a given soil with a standard amount of compaction effort.

The California bearing ratio (CBR) is a penetration test for the evaluation of the mechanical strength of Road sub-grades and base-courses. It was developed by the California Department of Transportation. I. Pavement Design.

California Bearing Ratio (CBR) test was developed by the California Division of Highway as a method of classifying and evaluating soil-sub grade and base course materials for flexible pavements. CBR test, an empirical test, has been used to determine the material properties for Pavement Design.

For subgrades with CBR values of 15% and above the sub-base should have a standard thickness of 150mm, a value determined as the minimum practical for spreading and compaction. For subgrades with CBR values in excess of 30% and a low water table or hard rock subgrades then the sub-base may be omitted.

The method of equivalent surface deflection is based on the premise that if a correct thickness of a capping layer of a certain CBR value is used over a subgrade with a certain CBR value, the two-layer system can represent a semi-infinite subgrade with a single design (effective) CBR

The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical strength of natural ground, subgrades and base courses beneath new carriageway construction. It was developed by the California Department of Transportation before World War II.

The basic site test is performed by measuring the pressure required to penetrate soil or aggregate with a plunger of standard area. The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material ^[1]. The CBR test is described in ASTM Standards D1883-05 (for laboratory-prepared samples) and D4429 (for soils in place in field), and AASHTO T193. The CBR test is fully described in BS 1377: Soils for civil engineering purposes: Part 4, Compaction related tests, and in Part 9: In-situ tests.

The CBR rating was developed for measuring the load-bearing capacity of soils used for building roads. The CBR can also be used for measuring the load-bearing capacity of unimproved airstrips or for soils under paved airstrips. The harder the surface, the higher the CBR rating. A CBR of 3 equates to tilled farmland, a CBR of 4.75 equates to turf or moist clay, while moist sand may have a CBR of 10. High-quality crushed rock has a CBR of over 80. The standard material for this test is crushed California limestone which has a value of 100, meaning that it is not unusual to see CBR values of over 100 in well-compacted areas.

${\displaystyle CBR={\frac {p}{p_{s}}}\cdot 100\quad }$

A Soil Boring Test is a type of geologic engineering test to determine the capability of the soil or to determine the strength and properties of a required building foundation.