Forging new generations of engineers

Forging new generations of engineers

SOILS Civil Engineering & ArchitectureTM Unit 4 - Lesson 4.5 - Activity 4.5.1 Soil Testing

Soil Testing

Introduction • Prior to developing a property for a commercial endeavor, a designer needs to investigate the soil conditions at the site. • There is no construction material that has both the physical and engineering properties which are more variable than soil. Therefore it is highly desirable to have some information regarding both the surface and subsurface soil conditions.

Soil – What is it? • Soils rarely exists as separate components such as sand or gravel. • Soils contain various particle sizes of gravel, sand, silt and clay and each contributes to the characteristics of the soil.

Why Test the Soil??? • The knowledge gained from soil testing allows the engineer to make estimates for: • Bearing Capacity of the soil • Settlements of Foundation ( amount and rate) • Earth Pressure – both lateral and vertical • Drainage These characteristics determine how certain soils behave as a construction material.

What is Needed to Determine Soil Properties • Site Plan • Site Profile (Contour Map) • Geological Information (USGS Maps) • Soils Sample Data(obtained through soils analysis/testing)

Factors to be taken into consideration when determining the type of the building foundations: • Function of the structure • Loads from the structure • Bearing capacity of foundation material • Total and differential settlement of foundation • Uplift forces acting on the foundation • Costs

The Soil Bearing Capacity needs to be determined before a foundation system can be designed. This can be determined by: • Local or State Building Codes • Uniform Building Code (UBC) • Soil testing/analysis • Site inspection and simple soil testing methods ( surface soils- top 1 foot) • Soil borings taken at proposed foundation locations (subsurface soils) • Presumptive Bearing Capacity

Sample Soils • Soil testing must be done on soil samples that truly represent the the soil at the site. • Soil sample about 1’-2’ below surface • Boring samples are taken at various locations and depths below the surface (subsurface) for deep foundations

Soils Testing • Unified Soils Classification System is a method for for identifying and grouping soils. It was first developed by Casagrande for military construction of airfields. • Many soils can be grouped visually with the USGS with additional tests for grain size and plasticity required to accurately classify the soil.

Unified Soil Classification System • The Unified Soil Classification System is a rapid method used to determine Simple Grain Size Analysis and categorizes the soil as either : • -Coarse-Grained Soils • -Fine Grained Soils • -Highly Organic Soils • Only particles sizes smaller than 3” are considered in the USC System

Coarse vs. Fine Grained Soils • Many soils can be grouped visually with the USGS and additional tests for grain size and plasticity are required to accurately classify the soil • Coarse-Grained soils described by grain size • Fine-Grained Soils described on the basis of their plasticity

Gravels range from 3” down to the size of peas Sieve Sizes • Silt and clay can pass through the #200 sieve

Sieves #40 sieve ( similar to window screen) #4 sieve ( ¼” squares, similar to hardware cloth)

GravelSand Boulder CobblesSilt & Coarse Fine Coarse Medium Fine Comparable Size: >12” 3”–12” ¾”–3” #4 - ¾” #10 - #4 #40-#10 #200-#40 <#200 Grain Size(Gradation) Clay NOTE: Particles finer than fine sand ( #200 sieve) can not be seen by the naked eye at a distance of 8 inches

Gravel Identification Coarse Gravel from 3” to ¾”, a comparable size – Plum or Lemon Fine Gravel from #4 to ¾”, a comparable size –Grape or Pea

Coarse gravel Gravel Size Fine gravel

Sand Identification Coarse Sand from #4 to #10, a comparable size - Rocksalt Medium Sand from #10 to #40, a comparable size - Sugar

Coarse sand Sand Size • Medium sand

Graded Soils • Soils can be defined by how the particle sizes are distributed within the soils sample. • Well-Graded Soils-have a good representation of all particle sizes from the largest to smallest • Poorly-Graded Soils-two types • Uniformly-soil particles are nearly the same size • Gap-Graded-contains both large and small particles but the graduation continuity is broken by the absence of some particle sizes

Clean vs. Dirty Graded Soils for Gravel and Sand • If a soil is identified as being “Clean” it contains little or no fines (<5%) • If a soil is identified as being “Dirty” it contains an appreciable amount of fines ( >12%) • Silty fines • Clayey

Soil Designations • The USCS divides soils that have been classified into the major soil categories by letter symbols, such as: • S for sand • G for gravel • M for silt • C for clay • O for organic • Pt for peat

Grain Shape

Soil Color • Color can aid in distinguishing soils types • Can vary with moisture content • May indicate the presence of certain chemical or impurities • Dark brown /black may indicate organic material • Gray, olive green indicate inorganic soils • Red or yellow may indicate iron oxides • Gray-blue or gray-yellow indicates poor drainage • White to pink may indicate considerable silica, calcium carbonate, or aluminum compounds.

Plasticity • Plasticity of the soils refers to the varying water content on the consistency of the soil in fine-grained soils. • This system is sometimes referred to as the ATTERBERG LIMITS, named after the Swedish scientist who developed this test. • Plastic Limit-lowest moisture content at which soils can be rolled into 1/8” dia.thread with out breaking • Liquid Limit- minimum moisture content at which soil will flow when a small shear or cutting force is applied

Soils Groups These letters are then used in combination to form the soils groups

Determining the Silt or Clay Characteristics of Fine Grained Soil • In addition to the Sieve Analysis the following tests will be done to determine of the Fine Grained soils • Dry Strength- crushing characteristics • Dilatancy- reaction to shaking • Toughness- consistency near plastic limit

Unified Soil Classification System Start here

Equipment for Testing • Sample of soil about the size of a coffee can and collected below the top soil horizon (about 1 to 2 feet). • 2 mason jars with tops • 5 gallon pail • Water • Mixing bowl • A 2’ x 2’ metal pan and rubber mallet • Sieve collection, ASTM No 4 and ASTM No. 40Bottom sieve pan and cover • Triple-beam balance or Digital Scale

Testing USCS SYSTEM SEIVE ANALYSIS

Weigh each sieve separately Weigh mason jars for later use

Take a representative soil sample from the property A shovelful or coffee can of soil should be enough Soils Sampling

Soil sample should be dry • Pulverize the soil with a rubber mallet

Continue to Pulverize the soil with your hands • Be sure that all small and large clumps are completely broken apart.

Stack sieves with Number 4 on top, then the Number 40 sieve below that, and then finally the bottom pan.

Place soil in Number 4 sieve, place cover on top and shake vigorously.

Shaking the Soil Sieves • Shake with up and downward motion • or / and • Shake with side to and side motion • Shake vigorously.

Weigh the sample material and the sieve. Subtract the weight of the sieve to obtain weight of soil. In this case , the weight of the particles is the Gravel fraction in the soil sample Do this for each sieve. Weighing of each Sieve with Sample Particles

#4 Sieve with Gravel

#4O Sieve with Sand • Record and subtract the weight of the No.40 sieve only (i.e., without the soil sample). The difference is the coarse and medium grained SAND fraction in the soil sample.

Bottom pan with Fines • Weigh the bottom pan and its contents. Record and subtract the weight of the empty pan. The difference is the fine SAND, SILT, and CLAY fraction of the soil sample.

Relative Particle Sizes #40 sieve #4 sieve

Sieve Analysis Results USCS Classification for Coarse Grained Soils • Coarse-grained soil, also called granular soil has more than half of the soil grains visible to the naked eye. • If the percentage of GRAVEL and SAND is greater than 50%, then the soil is a granular soil. • If the soil is predominantly coarse-grained, identify the soil sample as being gravelorsand by estimating whether 50% or more, by weight, of the coarse grains (GRAVEL and SAND) are larger or smaller than the No 4 sieve size.

USCS Classification for Fine Grained Soils • Fine-grained soils, also called cohesive soils contain greater than 50% SILT and CLAY particles. • It is classified further into either SILT or CLAY and them determined if it is high or low plasticity by estimating its drystrength (crushing characteristics), dilatancy (reaction to shaking), and toughness (consistency near the plastic limit) • Individual fine- grains are not visible to the naked eye

Determining the Fine Grained Sand Fraction of Soil • Place the contents of the bottom pan from the sieve test in a Mason jar. • Weigh and Record results • Fill jar with water so that I • it is ¾ full • Shake jar with lid on and let the fine sand settle 5 to 10 seconds • Drain off

Pour off the dirty water, be careful not to spill any of the soils at the bottom of jar • Repeat the shake,settle and drain off procedure several times • Repeat until water is clear • Determining the Fine Grained - • Sand, Silt and Clay fraction of the soil sample

Determining the weight of Silt and Clay in Soil Sample • Place the Mason jar, without top, and the contents into the oven and dry. • Weigh the jar and contents. Record the weight and subtract the weight of the empty jar. The difference is the fine grained SAND fraction in the soil sample. • Determine the weight of SILT and CLAY in the soil sample • Determine the percentage of Silt and Clay in the soil sample

Dilatancy Test • Dilatancy is the reaction to wet shaking • Prepare a pat of moist soils approximately 3/4 in3 in size • Add water, if necessary, to make soil soft but not sticky, like soft putty • Place pat in open palm of hand • Shake horizontally, striking with other hand several times

Forging new generations of engineers