Types of soil tests - Modified Proctor Test
There is many types of laboratory tests should be performed during a Geo-technical investigation or site construction work.
We will show here the most laboratory tests commonly used.
The procedures described to perform each test are matching with ASTM standard.
Modified proctor test (ASTM D1557)
- Test History
* The original "proctor test" was generated by R.R Proctor in 1933.
* ASTM test method D698 (often referred to as the "standard proctor") was very similar to the method proposed by R.R Proctor , with the exception that both ASTM test methods (D1557 and D698) use a free-fall drop of the hammer , in lieu of firm strokes ( which may give variable results).
* The modified proctor test was introduced as an ASTM standard in 1958.
* By 1970s and early 1980s the modified proctor become more widely used as a modern replacement for the standard proctor.
- The propose of modified proctor test
The modified proctor test determines the moisture content at which a give soil type will compact the best (i.e.,achieve maximum density).
The moisture -density relationship is determined by compacting a give volume of soil at a known moisture content into a standard -sized cylindrical mold. The maximum density test (ASTM- D1557) as described in this article is referred to as the " modified proctor"
- The different between the modified proctor and the standard proctor test
* The hummer weight at the standard proctor test uses is 5.5 Ib whereas in the modified proctor is 10 Ib.
* The height of the drop at the standard proctor is 12 inches whereas in the modified proctor is 18 inches.
* The number of layers placed into the mold is 3 layers in the standard proctor whereas in the modified proctor is 5 layers.
* The standard proctor creates an effort around 12400 ft-Ibf/ft3, whereas the modified proctor create a force approximately 56000 ft-Ibf/ft3.
Due to changing in the compaction equipment which become larger and heavier over the years it become necessary to have a higher, more relevant compaction standard .
Due to changing in the compaction equipment which become larger and heavier over the years it become necessary to have a higher, more relevant compaction standard .
- The misconception about different need for the standard and modified proctor test.
* One common misunderstanding is that 100% compaction obtained by the standard proctor is equivalent to a 95% compaction achieved by the modified proctor.
Since the different in load applied during each test is so great (12400 verse 56000 ft-Ibf/ft3) a 95% compaction determined by using a modified proctor is equivalent to more than 103% compaction as obtained by a standard proctor.
* One proctor work better in some soils than the other method.
The both tests are prepared in the lab for all soil types. However, technological engineers routinely adjusted the moisture and density required (compaction) in the field when utilizing the modified proctor dependent on the soil type of fill loading requirements.
- The test equipment
* Mold: 4 inch in diameter by 4.58 inch in height .
* Hammer: 10 Ib with an 18 inch drop and with a 2 inch circular face , may be manually or mechanically operate.
*Scales: a large scale with a 20 kg minimum capacity and a smaller 1 kg scale.
* Sample extrude : a hydraulic car jack or other adapted equipment to help remove the soil from the sample mold.
* Steel straight edge : approximately 12 inch long by 2 inch wide and having one beveled edge.
* Oven: thermostatically controlled to maintain a temperature of approximately 230 f (110 c).
* Mixing tools, mixing pans and moisture sample containers.
- Test procedure
* To start the test, obtain a large (50 Ib minimum) bulk sample from the field.
* Pass the materials through the # 4 sieve.
* The initial moisture content should be brought to a few percent under optimum by either adding moisture or by dry the soil , A good starting moisture is that at which when you squeeze the soil in your palm , it will just barely cling together .
* Divide the soil into 4 equal samples. each weighing about 2500 g. Label the samples from 1 through 4.
* Sample # 1 is already at the proper moisture content to begin the test and should now be sealed in an airtight container and labeled.
* Each successive sample should have between 1.5 % and 2 % more moisture added to it then the preceding sample. Thoroughly mix required water into each sample. seal each
sample in an airtight container and label it accordingly (+ 2%, + 4% etc).
* Leave the samples sealed to cure. So that the moisture is distributed evenly throughout 2 to 4 hours for non plastic soils, and up 16 hours for very clayey material. Incomplete curing is often the cause of inaccurate point on the curve.
* Place the compaction moil on a level concrete surface.
* Put on layer of soil (1/5 of the sample) from sample container # 1 into the mold.
* Compaction this first layer of soil with 25 blows from the compaction hammer, distributing the blows evenly over the sample surface.
* The hammer should be raised the full 18 inches then allow to drop in free fall to strike the soil.
* In a similar manner, compact the remaining four equal lifts of soil from sample container # 1 with the fifth and final compacted layer filling slightly higher than the horizontal split where the top of the mold separates.
* Separate and remove the top and bottom portions from the mold. Using straight edge trim off all excess material so that the soil is level with the top of the mold. Any small holes or voids should be filled with the trimmed material and then patted flush into place.
* Weight the mold and the soil , and then record the weight at the test sheet (same as below sheet example). Next extrude the soil from the mold.
* Weight the mold and the soil , and then record the weight at the test sheet (same as below sheet example). Next extrude the soil from the mold.
* Take a representative portion (approximately 500 g) of material axially from the central portion of the sample.
* Place this material in a number of containers and weight it on the smaller scale , and then enter the weight and container number on the test sheet
* Place the container in the oven to dry when dried, this sample will be weighted for the moisture calculation.
* Repeat the same procedure for sample # 2 through # 4. Being sure to obtain a moisture sample for each "point" pounded. An attempt should be made to compact two points on the dry side of the optimum moisture content and two points on the wet side. Four points separated in this manner will help to create a well - formed compaction curve.
* After moisture samples are dried, weigh them, record each weight on the test sheet.
* Place this material in a number of containers and weight it on the smaller scale , and then enter the weight and container number on the test sheet
* Place the container in the oven to dry when dried, this sample will be weighted for the moisture calculation.
* Repeat the same procedure for sample # 2 through # 4. Being sure to obtain a moisture sample for each "point" pounded. An attempt should be made to compact two points on the dry side of the optimum moisture content and two points on the wet side. Four points separated in this manner will help to create a well - formed compaction curve.
* After moisture samples are dried, weigh them, record each weight on the test sheet.
- Calculations
The calculation needed for the modified proctor are as the below:-
* First calculate the percent moisture
percent moisture = (W/D) * 100
where
W weigh of water (wet weight of soil and container) - (dry weight of soil and container)
and
D, weight of dry soil = (dry weight of soil and container) - (weight of container)
* Determine the wet density:-
wet density = {(weight of soil in grams) / (453.6)} * (30)
where
Weight of soil = (weight of compacted soil and mold) - (weight of mold)
* Determine the dry density
Dry density = (wet density) / (100 + percent moisture) * 100
* Plot each point (dry density versus moisture) on the test sheet graph, then draw a curve through them. The maximum density and optimum moisture content meet at the top of the curve.
In this article, we reviewed one type of soil tests, which is modified proctor test and in next article we will explain another type of soil test which is sieve analysis.
We are fully prepared to answer your inquiries via the Contact Us icon and we will get back to you as soon as possible.
In this article, we reviewed one type of soil tests, which is modified proctor test and in next article we will explain another type of soil test which is sieve analysis.
We are fully prepared to answer your inquiries via the Contact Us icon and we will get back to you as soon as possible.