Group 4 Science Project

Physics in the School Field:Soil Tests

TeddySpencer

Introduction• We chose the field because we heard that

several people using it have gotten injured after slipping.

• We also learned that the school was unhappy with the field’s conditions and was planning to rebuild it.

• So we carried out several experiments to scientifically determine the suitability of our current field.

• From the results of the experiment, we can then determine whether the field is indeed unsuitable and suggest ways to improve its safety and usability.

Hypothesis

The characteristics of a good field are:• high grip,• good drainage, • not easily compacted• suitable for the growth of grass

We predict that the field has none of these

characteristics.

Part A: Soil Friction Tests

• Many parts of the field, especially those that are heavily used, are completely bare.

• We wanted to see how much this affects the friction of the field and whether it was a safety concern.

• We also compared different parts of the field under wet and dry conditions to determine how much the friction of the field is affected by rain.

Part A: Method

• First, we used a school shoe and put it onto various elements on the field such as clay patches or grassy patches.

• Using a Newton metre we measured the required force to start moving the shoe. We carefully increased the force on the shoe and recorded the final force when the shoe started moving.

• We put a 1kg mass at around the centre of the shoe to make sure the pulling of the Newton metre does not cause a lifting force which would cause less surface to touch the ground and give smaller results. We also applied some force on the shoe to embed it a bit to the ground to resemble normal walking motion.

Soil Friction Test Results

Soil Type

Force needed to move the shoe (N) Coefficient of static Friction

1 2 3 Average

Very grassy 9.8 14.0 11.6 11.8 0.851

Patchy grass 10.2 9.6 9.1 9.6 0.692

Clay 6.0 6.7 5.2 6.0 0.433

Sandy Clay 7.2 5.8 6.2 6.4 0.462

Wet Grassy 8.0 8.0 7.0 7.7 0.555

Wet Patchy 7.0 7.2 7.8 7.3 0.526

Wet Clay 6.2 5.8 6.0 6.0 0.433

Wet Sandy Clay

4.2 4.4 6.0 4.9 0.353

Weight of Shoe + 1kg load = 13.867N

Part A: Conclusion and Evaluation

• In our research, “Nelson & Associates” States that 0.50* Coefficient of Static Friction is the minimum safety standards for outdoors.

• This means that the Clay patches do not meet the standards especially when wet which decreases the coefficient of friction.

• The school should pick soil that is better for grass growth so if they actually rebuild the field, try to avoid using clay.

• We could have used sport shoes in our experiment to check if they would pass the standards that the school shoes did not

• However as explained in the method, sport shoes have very different soles and some have protruding soles such as football boots which have a lot more friction and we can’t generalize all the different types of shoes. Furthermore some shoes have already been subjected to a lot of wear and tear which decreases the friction of the soles.

*Coeffiction of Static Friction Standards from: http://www.hazardcontrol.com/sliptrip.html; Credentials: http://www.hazardcontrol.com/gnelson.html

Part B: Water Absorption Tests

• From part A, we found that water has quite a profound effect on the friction of the field, especially the grassy parts.

• After raining stops, puddles of water are usually left in the field which, if not drained, will leave the field dangerous for a long time.

• Also if the field is flooded for too long the roots of the grass will die* because they can’t breathe underwater causing a reduction in grassy patches and an increase in injury prone clay patches.

*http://www.allaboutlawns.com/lawn-maintenance-care/watering/surviving-a-flood.php

Part B: Method

• Equipment – Measuring cylinder, stopwatch• First, we filled the measuring cylinder with water.• Then, we quickly overturned the cylinder over clay soil.• After that, we started the timer and measured the volume

of water.• After an hour, we measured the volume again and

stopped the timer.• We repeated the experiment for sandy clay, patchy

grass and heavy grass areas.

Soil Water Absorption TestsSoil

Type

Starting Volume

(ml)

End Volume

(ml)

Difference (ml)

Time (hours)

Drainage rate

(ml/hour)

Clay 330 290 40 1:01 39.34

Sandy Clay

550 450 100 1:00 100.00

Full Grass 360 250 110 0:30 220.00

Patchy Grass

300 230 70 1:00 70.00

Part B: Conclusion and Evaluation

• From our results, we found that bare clay soil has very poor drainage while areas with lots of grass tend to vastly higher drainage rates. Sandy clay also had a higher drainage rate compared to plain clay.

• Therefore, it is obviously better to have soil that is suitable for grass growth and also with a small percentage of sand to improve drainage.

Part C: Soil Compaction Tests

• If the soil is not compacted enough, the water from the rain would soak through the ground very quickly leaving the soil too dry for the grass roots to absorb enough water to survive.

• If the soil is too compacted, the roots of the grass cannot breathe properly as the air cannot go through the ground easily. This is even worse when it rains because the water does not move very quickly and causing the roots to deplete the air too quickly.

• We would need to find a very good mixture of clay, sand and silt to promote growth of grass and to do this we should analyse the ratio of the composition of the ideal soil where there is a lot of grass.

Part C: Method• Determine 4 different patches for testing, 2 from where grass is

growing and 2 from where grass is not growing.• Collect around soil up to a depth of around 2cm which is about the

depth the grass roots reach.• Leave the soil to dry and remove the grass, roots and humus lumps.• Transfer the soil to a larger, plastic cup, which does not crack as

easily and record the weights.• Shuffle each sample for around 5 minutes to loosen the soil and

record the volume of the soil.• Trample each soil sample using a large mass for around 5 minutes

to compress them and record the new volume of the soil.• Calculate the density of the samples when loose and when

compressed and then find the percentage difference before and after.

Soil Compaction Tests

Soil Type Volume (cm3) Soil Mass

(g)

Density (g/cm3) Compaction

(%)Start End Start End

Dry Clay 210 130 232 1.10 1.78 61.82

Dry Sandy Clay

400 330 480 1.2 1.45 20.83

Moist Clay 490 360 483 0.99 1.34 35.35

Wet Clay 410 260 488 1.12 1.88 67.86

Part C: Conclusion and Evaluation

• The patchy grass soil seems to resemble sandy clay while the grassy soil seems to resemble the clay soil.

• Sandy clay might have been too compact already so there's not much grass there so if we add more compressible clay it’s compressibility is close to that of patchy grass.

• A main constituent in the grassy soil may be clay.

Part D: Soil Texture Analysis

• In this final test, we tried to determine the soil texture of the field, which is determined by the ratio of the different aggregates in the soil: clay, silt and sand.

• From the results, we can then determine which aggregates should be increased and decreased and roughly by how much.

Part D: Method1) Pour soil into a beaker until it fills up one-third of the

beaker.2) Pour in water till two third of the beaker is filled. Add in a

bit of detergent to help break up the soil.3) Pour the mixture into a jar, close the jar and shake

vigorously for 30 seconds. After this, quickly pour it back into the beaker.

4) Leave the soil in the beaker to settle for a week.5) Measure the height of each individual aggregate layer

and determine the percentage of each aggregates.6) Determine the soil texture type by comparing it to a soil

texture triangle.

Soil Texture Analysis ResultsAggregate Percentage (%)

Clay 30

Silt 50

Sand 20

Part D: Conclusion and Analysis

• By using the soil texture triangle below we determined that the soil in our field is called silty clay loam.

• However the soil sample taken was taken from very near the surface of the field and might not be a perfect representation of the actual soil composition of the field.

• Furthermore, the method used for determining the soil composition is quite crude.

Diagram from: http://web.ukonline.co.uk/fred.moor/soil/formed/f0107.htm

Failed Experiments

• Temperature of Ground

Overall Conclusion and Evaluation