Soils Lab 2. Compaction - guidance and results for online lab PDF

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NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

Soils Laboratory 2: Soil compaction tests (lab handout) This document provides guidance (and example lab test data) for students who did not attend a face-to-face Soils Lab 2 session. Students who did attend a face-to-face Soils Lab 2 may also find the guidance in this document useful as a reminder of lab procedures and processes. Introduction The activities for Soils Lab 2 involve conducting tests relating to compaction properties of soil, on different samples of clay: 





The British Standard (BS) Compaction Test (BS 1377-4), which determines the optimum moisture content (OMC) and the maximum dry density (MDD) of clay soil. The Moisture Condition Value (MCV) test (BS 1377-4), which assesses how much compactive effort (energy) is required to fully compact a sample of soil. The Sand Replacement Test (BS 1377-9), to assess the density of insitu compacted soil at a site (this test is conducted in the lab on a simulated compacted soil).

The procedures required to conduct these tests are outlined in the Week 20 ‘Soil Activities’ section of the DESN10041 module room on NOW. Students should ensure they are familiar with this content before attempting to produce the soils lab report for this module. Soils Lab 2 objectives   

To introduce students to soil compaction measurements. To determine the compaction characteristics of a clay soil. To calculate in-situ density using sand replacement.

Students are required to: 1. Study the relevant information from Week 20 (see above). 2. Conduct/observe Soils Lab 2 activities, as directed by staff during a timetabled soils lab session in the geotechnics/soils lab (Maudslay 113). 3. Use the results collected during Soils Lab 2 to complete the results sheets & questions in this document. 4. Include relevant results from this lab in Assessment Brief 5* (Soils Lab Report), to be submitted before 10th May 2021 (Term 3). * See Assessment Brief 5 (Soils Lab Report) on NOW for details. The Soils Lab Report will include activities from both soils labs (Soils Lab 1 & Soils lab 2).

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

Laboratory activities 1. BS Compaction Test (BS1377, Part 4: 1990) A total of 5 samples of (the same clay) soil are used to determine the test results. Each group of students in the lab will complete one compaction test, and the additional results will be made available. All results should be recorded on Form 4A (see below) in order to produce a graph to establish the maximum dry density and optimum moisture content of the soil. Description of lab activities: In the lab session, the method detailed in British Standard 1377 part 4 (BS 13774) is followed. Use the exemplar results provided in Form 4A below (taken from BS 1377-4), to complete the data/results calculations required. The exemplar data provided for this test (Form 4A) includes data from tests on 5 specimens of soil, each of which was prepared at a different moisture content and then compacted. For each soil specimen, the activity was as follows: The lab technician compacts a sample of clay soil into a metal container by placing it into a mechanical compactor. The metal container consists of a ‘collar’ a ‘mould’ and a ‘base’. Collar Mould

Base

Figure 1. Compaction mould

Figure 2. Mechanical compactor

In the mechanical compactor, the clay soil is compacted in 3 layers, using a 2.5kg rammer dropped 27 times per layer. Once the soil is compacted, the collar is removed (leaving the ‘mould & base’) and the soil is levelled off at the top of the mould (see Figure 3). Once levelled off, it means that the volume of compacted soil is the same as the volume of the mould (= 1000 cm3).

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component) The mass is then recorded on Form 4A (below) as “Mass of mould + base + compacted specimen (m2)”. The “Mass of mould & base (m1)” has been previously recorded and so students can determine the “Mass of compacted specimen (m2 – m1)” in Form 4A. Figure 3. Levelling off compacted soil

Once the “Mass of compacted specimen (m2 – m1)” is determined, students can then calculate the “Bulk density ρ” (using the equation in Form 4A: if units of g for mass and cm3 for volume are used, the density result is in units of Mg/m3). However, when conducting compaction, the “Dry density ρd” is normally reported, because it provides a much more consistent measure of how densely the soil particles are packed (on-site, the bulk density of soil can change with changing moisture content – for example if it rains - but the dry density will remain unchanged). Form 4A provides an equation for students to determine dry density, if the moisture content is known. In the exemplar results, the lab technician has determined and reported the moisture content (ω) for each of the 5 compacted specimens. Once the bulk density (ρ) and moisture content (ω) are known for each of the 5 compacted specimens, students then use the equation in Form 4A to determine the dry density (ρd) of each specimen (Dry density, ρd = [100 x ρ] / [100 + ω]). For example, if:

Bulk density (ρ) = 2.10 Mg/m3 Moisture content (ω) = 15 %

Then:

Dry density, ρd = [100 x ρ] / [100 + ω] Dry density, ρd = [100 x 2.10] / [100 + 15] Dry density, ρd = 1.83 Mg/m3

So, you now have data from 5 specimens of the same soil type: Each specimen will have a dry density and a moisture content. Using Form 4A (or Excel) a graph can then be plotted of moisture content against dry density. If you draw a best fit curve through the 5 points, you should be able to identify a peak in the best fit curve. This peak can be used to determine and report the ‘Maximum dry density’ and the ‘Optimum moisture content’ (see soils video ‘Week 20. Compaction – OMC & MDD’ on NOW for further details).

Form 4A

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

2. Moisture Condition Value Test (BS1377, Part 4: 1990)

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

1.5kg of loose soil is placed in the cylindrical mould, and the penetration of blows from a standard rammer, compacting the soil, is recorded in Form 4C (see below). In Form 4C, the difference in penetration between blows is plotted against the number of blows. A best-fit line is then plotted through the steepest part of the points. On the steepest best-fit line, identify the point where it crosses the 5mm change in penetration line. From this point, the MCV result may be read directly from the lower horizontal axis of the chart. Description of lab activities: In the lab, the method detailed in British Standard 1377 part 4 (BS 1377-4) was followed. Use the exemplar results provided in Form 4C below (taken from BS 1377-4), to complete the data/results calculations required (see below). The exemplar data provided for this test (see Form 4C) includes data from a test on 1 specimen of clay soil. The activity was as follows: 1.5kg of loose clay soil is placed in to a cylindrical container. The container is then placed in to the MCV apparatus, beneath a standard 7kg rammer. The rammer is then released (from 250mm height), and the “Penetration or protrusion” (see Form 4C) of the rammer in to the container is measured by noting the value on a scale on the side of the rammer against the top of the container.

Figure 4. MCV apparatus

Rammer being dropped

Container of soil

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

Figure 5. MCV apparatus in use

The rammer is repeatedly raised and dropped, and the penetration after the number of drops (“Total number of blows” stated on Form 4C) is recorded. Once the same value of penetration is recorded twice in a row for subsequent numbers of drops, it indicates that the soil is fully compacted. So, that same penetration value (95mm in the exemplar results) can be entered for the rest of the rows in Form 4C because the soil is fully compacted, and the penetration value would not change no matter how many further drops were continued. Then, on Form 4C, the results in the column “Change in penetration n to 4n” are determined by students: To do this, look at row 1 (i.e. the data for “Total number of blows” = 1). In this row, n = 1, so the column “Change in penetration n to 4n” is determined by looking at the change in penetration from blow number 1 to blow number 4. In the   

exemplar data, this would be: For blow number 1, penetration = 54mm For blow number 4, penetration = 77mm Therefore the change in penetration = 77 – 54 = 23mm

So, in the column “Change in penetration n to 4n”, a value of 23 is entered. Then this process is repeated for the other rows: In the exemplar data, for the row where “Total number of blows” = 2, the “Change in penetration n to 4n” is the difference between the penetration after 2 blows (= 67mm) and the penetration after 4 x 2 blows, i.e. 8 blows (= 89mm). Then the next row is the difference between the penetration after 3 blows and the penetration after 12 blows, and so on. Once a value = 0 is entered for “Change in penetration n to 4n”, all subsequent rows are also = 0. Then, using Form 4C, students draw a graph of results where the total number of blows (across the top of the graph) is plotted against the change in penetration (vertical y-axis on the graph). The resulting points should be joined with a smooth curve. On this curve, find the section with the steepest gradient, and extend this section (in a straight line) down through the 5mm change in penetration line. At the point where the steepest straight line meets the 5mm change in penetration line, go straight down and read off the value along the bottom of the graph: this is the MCV (moisture condition value) for the soil (see soils video ‘Week 20. Compaction - MCV’ on NOW for further explanation and guidance on how the MCV is determined from your results).

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

Form 4C

1500 23.9%

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

3. Sand Replacement Test (BS1377, Part 9: 1990) This test is intended for use on-site, to determine the density of in-situ soil in the ground. The method involves excavating a hole in the ground and then using a pouring cylinder (see Figure 6) to fill the hole with a sand of a known density. If the mass and density of the sand used to fill the hole is known, and the mass of excavated soil from the hole is known, then the density of the excavated soil can be determined. On-site excavation cannot be done within the lab, so the lab activity involves using a concrete block shaped to simulate an area of ground that has had a hole excavated in it. From this simulated ground, a hole has been excavated: 



Mass of compacted soil removed from hole o i.e. “Mass of wet soil from hole (mw)” on Form 9a =

1618g

Establishing moisture content of excavated soil: o Mass of container = 30.50g o Mass of container & wet soil = 75.05g o Mass of container & dry soil = 71.00g

Description of lab activities: In the lab, the method detailed in British Standard 1377 part 9 (BS 1377-9) was followed. Also, the soils video ‘Week 20. Compaction – Measuring density’ on NOW includes further explanation and an overview of the method. The exemplar data provided for this test (in Form 9a below) includes data from one test. Also, the information given above for the “Mass of wet soil from hole (mw)” and for establishing moisture content of excavated soil is required. Using the Form 9a exemplar data, the lab activity involves Calibration (firstly to determine the mass of sand required to fill the cone of the cylinder, and then also to determine the bulk density of the sand) before the Sand replacement density test is then conducted. Calibration (to determine the mass of sand required to fill the cone): The first issue is that when sand is poured from the pouring cylinder, it not only fills the excavated hole, but also fills a small ‘cone’ at the base of the cylinder (see Figure 6). So, during a test, the amount of sand poured from the cylinder is actually the amount required to fill the hole and also to fill the cone (see the video ‘Week 20. Compaction – Measuring density’ on NOW). We only want to know the amount of sand filling the excavated hole, so before we conduct a ‘sand replacement density test’ we must determine how much sand fills the cone (in order to be able to deduct that from any calculations). To do this, sand is poured on to a flat surface (the surface of the lab desk), so that sand fills only the cone, and the pouring cylinder is weighed before and after

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component) pouring. In the exemplar Form 9a results, the data included under ‘Calibration’ next to ‘Mean mass of sand in cone of pouring cylinder (m2)’ reports this information, with the mass of sand required to fill the cone (m2) = 432.0g.

Pouring cylinder (containing sand)

Cone of cylinder

Calibrating container (volume, V = 1022ml)

Figure 6. Pouring cylinder

Calibration (to determine the bulk density of the sand): Next, we need to determine the bulk density of the sand used in the pouring cylinder. To do this, sand from the pouring cylinder is poured in to a ‘calibrating container’ of a known volume, V (1022 ml). When sand is poured in to the calibrating container, it fills the calibrating container and also fills the cone of the pouring cylinder. Hence, in the exemplar Form 9a results, the difference between the ‘Mass of sand before pouring (m1)’ (5867.8g) and the ‘Mean mass of sand after pouring (m3)’ (3974.2g) includes the sand required to fill both the calibrating container AND the cone. So, the mass of sand to fill only the calibrating container, ma is = m1 – m3 – the mass of sand to fill a cone (m2). The bulk density of the sand, ra, is then calculated by mass (ma) / volume (V). There is no need to change any units because “g/ml” gives the same units as “Mg/m3” (which is commonly the unit used for reporting soil density). Conducting the sand replacement density test: Once the above has been completed, the sand replacement density test is then conducted. As stated earlier, on-site a hole would be excavated from the soil in the ground, but in the lab the hole in the concrete block is used to simulate a hole in the ground.

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component) As we already know, the amount of sand poured from the cylinder is actually the amount required to fill the hole and also to fill the cone. During Calibration it was determined that:  The mass of sand required to fill the cone (m2) = 432.0g So when sand is poured in to the hole in the concrete block, the data presented in the Form 9a exemplar results sheet (data entered below the row marked “Test number”), shows :    

Mass Mass Mass Mass

of of of of

wet soil from hole (mw), i.e. mass of soil excavated from the hole sand (in pouring cylinder) before pouring (m1) sand (in pouring cylinder) after pouring (m4) sand in the hole (mb)

Concrete block (simulating soil in the ground)

Poured sand, filling hole, plus cone on top of hole

Hole within concrete block (simulating hole excavated in ground) filled with sand

2nd hole within concrete block (simulating another hole excavated in ground): not used during this test Figure 7. Sand poured in to hole in concrete block

From the data provided, students determine the ratio mw/mb (i.e. the ratio of the mass of soil excavated (i.e. ‘Mass of wet soil from the hole’) to the ‘Mass of sand in the hole’). Next, students can then determine the bulk density of the excavated soil, r, by multiplying this ratio by the bulk density of the sand (i.e. r = mw/mb x ra). Then, students need to determine the dry density of the excavated soil. To do this students first need to calculate the moisture content of the soil excavated from the hole, by using data provided earlier. Remember: Moisture content (%), ω = (mass of moisture / mass of dry soil) x 100 Finally, once the moisture content (ω, reported as a %) has been determined, the equation at the end of Form 9a is used by students to determine and report the dry density rd of the excavated soil (= [100 x r] / [100 + ω]).

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

(See soils video ‘Week 20. Compaction – Measuring density’ on NOW for further explanation and guidance on determination of your results).

NOTTINGHAM TRENT UNIVERSITY Module DESN10041 Engineering Materials (Soils component)

Soils laboratory coursework Assessment Students knowledge of soils will be assessed via a single laboratory report, covering tests conducted in both Soils Lab 1 and Soils Lab 2. It will contribute 25% of the coursework component of the module (i.e. 18.75% of the total module grade). It is to be submitted by 10th May 2021 in Term 3 (see Assessment Brief 5 on NOW, which contains the specific requirements for the report, and task specific assessment criteria). BS 1377, including all relevant forms, can be found using the British Standards online database (go to https://www.ntu.ac.uk/m/library click on ‘OneSearch’ then click on ‘Databases’ and find the ‘British Standards’ database).

Photo sources: www.ele.com www.youtube.com/watch?v=AP-lvZqLDYM Dr Rob Evans...