1. Introduction to Soils Testing & Mechanics
Prepared by:
Marcia C. Belcher, P.E.
Construction Engineering Technology

2. Geotechnical Engineering
Investigation of site conditions
Evaluation of soil properties, ie.:
plasticity (shrinkage/swell)
bearing capacity
permeability
shear strength

3. What is A Geotechnical Engineer?
Expert soils consultant for:
Structural engineer
Environmental engineer
Forensics

4. What does the Geotechnical Engineer Do?
Visits the site
Takes soil borings (crews perform drill)
Samples soil
Laboratory testing of soil (lab technicians)
Report and recommendations

5. Soil Defined Definition of soil:
                                                                                         
Definition of soil:
aggregate of loose minerals and organic particles
“loose” distinguishes soil from rock

6. Soil Components Soil is primarily a mixture of gravel sand clay silt
                                                                                          
Soil is primarily a mixture of
gravel
sand
clay
silt
organic material

7. Describing Soil Types
If a soil is a mixture of components, it is given the name of the greatest component
For example:
silty clay
sandy clay
sandy loam
Greatest Component

8. What is “Moisture Content”
Amount of water vs. amount of solids
Notation for moisture content:
w% = (Mw/Ms)x 100%

9. Why Do We Care? Water affects soil behavior: Let’s consider sand
dry sands are soft
moist sands are stiffer (beach driving)
wet sands are “fluid” (quicksand)

10. Driving on the Beach

11. Moisture Content of Soil
Let’s consider clay soils:
dry clay is very hard and stiff
Wet clay is difficult to compact
wet clay is soft and sticky
shrink and swell

12. Dry Clay Looks Like This!

13. Moist Clay Soils Can Look Like This!

14. Wet Clay Looks Like This!

15. Why Do We Care? If we are going to build a structure:
We must know the natural moisture content of the soil (aka “existing conditions”)
We must know the “optimum” moisture content of the soil for proper compaction (“required conditions”)
Many equations used in soils engineering require the moisture content to be known.

16. SPECIAL IMPORTANCE Moisture Content
For clays, an optimum moisture content exists for maximum compaction
Good compaction means our foundations won’t settle!!
Moisture content is also important during laboratory procedures used to identify engineering properties of soils.

17. Performing the Moisture Content Determination Test (ASTM D-2216)
Apparatus:
Soil
Tin Cups (3)
Drying Oven
Gram Scale (.1g readability)

18. Minimum Mass of Soil Sample
Max. Particle Size
Sample Size
≤ 2 mm
20g →
CLAY
4.75 mm
100g →
SAND
9.5 mm (3/8”)
500g
19 mm (3/4”)
2.5kg
GRAVELS
37.5 mm (1.5”)
10 kg
75 mm (3”)
50 kg

19. Sampling Sand Mix thoroughly using a metal scoop
Specimen must represent water condition of entire amount of material
Select representative sample of adequate amount (100g min for sand)

20. Sampling Clay
Trim outside edges of the material to remove edges that are dryer than the rest of the sample.
Use a knife or cutting wire to slice away a representative sample. (20 g min. for clay)

21. Label Three Tins Your group number followed by “a”, “b” and “c”
Example: 1-a, 1-b, 1-c
THESE WILL BE YOURS ALL SEMESTER LONG!! KEEP TRACK OF THEM!!

22. Lab Tests (Avg. of 3): Record mass of empty drying tins/lids (g)
Place samples in tins & apply lids
Record mass of samples in tin w/lid (g)
Dry samples at 110º C ± 5º until constant weight.
Remove from oven and record mass of dry samples & tin/lid.
Complete data sheet in lab manual (Chapter 4)

23. Moisture Content Equation
Dry weights will be posted on the class website.
Be sure your cans are labeled accurately.
w% = (Mw/Ms)x 100%