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(SAND REPLACEMENT METHOD)
ABSTRACT
This paper sets out the procedures for the determination of insitu dry density, moisture content and the percentage of compaction of soil on the structural layers of a carriage way using sand replacement method.
It is advised to obtain a percentage value of over 100% in practical constructions.
INTRODUCTION
Insitu density of soil is the process of determining the dry density, the moisture content and the percentage of compaction of soil in the field.
This can only be achieved by laboratory compaction test carried out on the same soil type to produce a ratio between the field and the laboratory compaction.
These parameters are used as the basis to control the process of filling for satisfactory result at reasonable cost. It is also applicable to soil at the formation level before any filling work is done.
Many civil engineering structures, for example: carriage way (road); requires the use of imported material for filling which is done in layers not exceeding 300mm and compacted to a degree of less about 100% until the sub grade and the subbase layer is achieved.
Field compaction is usually effected by mechanical means such as rolling, ramming or vibrating, etc.
METHOD OF DETERMINING THE INSITU DENSITY OF SOIL
There are several method of determining the insitu density of soil,
1. Proctor penetrometer method
2. Balloon density method
3. Core cutter method
4. Sand replacement method
SAND REPLACEMENT METHOD
This method is used to determine the insitu density of compacted fine, medium and coarse grain soils at layers not exceeding 150mm thick, using sand pouring cylinder
APPARATUS
1. Standard sand pouring cylinder
2. Base plate with 100mm diameter hole
3. Suitable tool for excavating hole such as hammer, chisel, tape, brush, nails, scraper and bent spoon
4 Weighing balance readable and accurate to 1g
5. Speedy moisture testing kit
6 A cylindrical metal calibrating container
7. Glass plate
8. Storage container
MATERIAL
Clean graded sand
CALIBRATION OF APPARATUS
Calibration to determine the mass of sand in the cone.
The procedures is as follows,
• The pouring cylinder shall be filled so that the level of the sand in the cylinder is within 15mm from the top, that is sand before pouring ( ). This shall be maintained throughout the test for which the calibration is used. A volume of sand that will fill up the calibrating can which is equivalent to that of the excavated hole is allowed to run out.
• The shutter of the pouring cylinder shall be closed and the cylinder placed on a glass plate.
During this process the pouring cylinder should not be tapped or otherwise be vibrated, when no further movement of sand takes place in the cylinder the shutter shall be closed and the cylinder carefully removed
The sand that has filled the cone of the pouring cylinder shall be collected and weighed, it shall be repeated for three times and the mean mass taken ( )
Calibration to determined the bulk density of the graded sand.
The procedure is as follows,
• The internal volume V of the calibrating can shall be determined from the mass of water required to fill it
• The pouring cylinder shall be placed concentrically on the top of the calibrating can after being filled to the constant mass. The shutter shall be open and sand allowed to run out, during this operation the pouring cylinder shall not be tapped or otherwise vibrated.
When no further movement of sand takes place in the cylinder the shutter shall be closed and the cylinder shall then be removed and weighed. This measurement shall be repeated for three times and the mean mass taken.
LET’S GO TO THE FIELD
Excavation of hole and the pouring cylinder placed over the hole.
• A flat area approximately 450mm square of the soil to be tested shall be exposed and trimmed down to level surface, preferably with scraper
• The metal tray shall be laid on the prepared surface of the soil with a hole over the portion of the soil to be tested using the hole as the pattern to excavate a round hole of 100mm diameter and depth of 150mm maximum. No loose material material shall be left in the hole and the immediate surroundings to the hole shall not be distorted. The tray shall be removed before the pouring cylinder is placed over the excavated hole.
• The excavated soil shall be carefully collected and weighed
• A representative sample of the excavated soil shall be used to determined the percentage of moisture content using speedy moisture tester.
• Filled the pouring cylinder to a constant mass and place so that the base of the cylinder covers the hole concentrically.
• The shutter shall be open and sand allowed to run out, during this operation the pouring cylinder shall not be tapped or otherwise be vibrated. When no further movement of sand takes place in the cylinder the shutter shall be closed and the cylinder shall then be removed and weighed.
CALCULATIONS
• THE MASS OF SAND REQUIRED TO FILL THE CALIBRATING CYLINDER ( )
Shall be calculated from:
• THE MASS OF SAND REQUIRED TO FILL THE EXCAVATED HOLE ( )
= mass of excavated soil (g)
= mass of sand required to fill the hole (g)
= the bulk density of sand ( )
• MOISTURE CONTENT OF THE SOIL (w)
This is obtained from the speedy moisture testing equipment.
• 6. THE DRY DENSITY
• PERCENTAGE OF COMPACTION
• EXAMPLE:
Assumed values
CONCLUSION
Sand replacement method of determining the dry density, moisture content and the percentage of compaction of soil in the field can only be achieved by carrying out compaction test on the same soil sample in the laboratory so that the field result should be compared during filling and compaction on site.
This compaction analysis is very necessary, since it is the basis of structural failures on roads.
REFERENCE
McCarthy, David F. (2007). Essentials of
Soil Mechanics and Foundations. Upper Saddle River, NJ: Pearson Prentice Hall.
p. 602. ISBN 0-13-114560-6.
Das, Braja M. (2002). Principles of
Geotechnical Engineering. Pacific Grove, CA: Brooks/Cole. p. 105. ISBN 0-534-38742-X.
"Automatic Soil Compactor".
