INTRODUCTION TO SOILS TESTING & MECHANICS Prepared by: Marcia C. Belcher, P.E. Construction Engineering Technology
Jan 17, 2016
INTRODUCTION TO SOILS TESTING & MECHANICSPrepared by:
Marcia C. Belcher, P.E.
Construction Engineering Technology
Geotechnical Engineering
Investigation of site conditions
Evaluation of soil properties, ie.: plasticity (shrinkage/swell) bearing capacity permeability shear strength
What is A Geotechnical Engineer? Expert soils consultant for:
Structural engineer Environmental engineer Forensics
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
Soil Defined
Definition of soil:
aggregate of loose minerals and organic particles
“loose” distinguishes soil from rock
Soil Components
Soil is primarily a mixture of gravel sand clay silt organic material
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
What is “Moisture Content”
Amount of water vs. amount of solids
Notation for moisture content:
w% = (Mw/Ms)x 100%
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)
Driving on the Beach
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
Dry Clay Looks Like This!
Moist Clay Soils Can Look Like This!
Wet Clay Looks Like This!
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.
SPECIAL IMPORTANCEMoisture 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.
Performing the Moisture Content Determination Test (ASTM D-2216) Apparatus:
1. Soil2. Tin Cups (3)3. Drying Oven 4. Gram Scale (.1g readability)
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
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)
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)
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!!
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)
Moisture Content Equation
Dry weights will be posted on the class website.
Be sure your cans are labeled accurately.
w% = (Mw/Ms)x 100%