Soil Test and Surveys
Post on 16-Jul-2015
SOIL TEST AND SURVEYS1Test for the Particle SizeThe sieve analysis is the process used to det. the particle sizes for gravels and for coarse and fine sands. A sample of the materials is thoroughly dried and then shaken through a series of sieves ranging from coarse to fine and the amount on each sieve is weighed and recorded. The AASHTO standard sieve sizes for soil aggregate are as follows: _________________________________________Sieve Designation in inches 2 1 1 3/8 4 10 40 200_________________________________________By Number Opening in Millimeter 50 37.5 25.0 19.0 9.50 4.75 2.00 .425 .075_________________________________________ Materials that are finer than the no. 200 sieve (.075 mm) is not feasible for determining the particles size.Test Methods to Evaluate the Effect of MoistureThe AASHTO Designation T 89 on LIQUID LIMIT signifies the percentage of moisture at which the sample changes by decreasing the water from liquid to a plastic state. The Plastic Limit- AASHTO Designation T-90 signifies the percentage of moisture wherein the sample changes with lowering wetness from a plastic to semi-solid condition.
The Plastic Index - AASHTO Designation T-90 is defined as the numerical difference between its liquid limit and its plastic limit. It is also referred to as a percentage of dry weight. Shrinkage Test (AASHTO Designation T-92)-the test measures the changes in volume and weight that occur as a party mixture of soil (except sieve no. 40) and the water.
Hand Feel Test-experienced soil engineers employ the hand-feel test to approximately predict the plasticity index of the soils. These test may include:
1. Thread toughness at a moisture content approximating the plastic limit. 2. The air dried strength 3. Dilatancy
Sand Equivalent Test (AASHTO Designation T-176)-the sand equivalent is the ratio between the height of the sand column(lab. experiment test) and the combined height of the sand and the expanded saturated clay which are expressed in percentage. Density Test of Soils- the density of soil or weight per cubic foot varies with the peculiarities of the soil itself, the moisture content, and the compactive device, plus the method of their use:
The Specific Gravity of the Soil Particles themselves - which may vary from 2.0 to 3.3 but usually is between 2.5 and 2.8. The particle size of the distribution of the soil a mass composed entirely of spheres of one size in the densest possible condition will contain 75% solid and 25% voids. The smaller the sphere in the mass the higher the percentage of the solid, hence, particle size distribution may greatly affect density.The grain shapes of soils particles sharp angular will resist shifting from a loose to a compacted state.. Flaky particles in soil will decrease its density because they are difficult to compact.Laboratory Test for Soil DensityTest for density maybe divided into two classes:Laboratory test to set a standard for density.Field test to measure the density of soil in place in the road wayLaboratory test maybe subdivided into three, according to the basis of compaction procedure.Static testDynamic or Impact testTamping foot or kneading-compaction test. Static test - to determine the maximum density of laboratory samples a sample of about 5000 grams of soil containing a specified percentage of water is placed in a cylinder mold 6 (15cm.) in a diameter and 8 (20cm.) in height. The dynamic or Impact test- samples of soil each containing a designated percentage of water are compacted in layers into molds of specifies sizes. Tamping foot or Kneading compact test- material is fed into a rotating mold and is compacted by several repetitive loads applied through a tamping shoe shaped like a sector of a circle.
The Strength testSoil test to determine the strength of soil are divided into:
Test for load carrying capacity for foundation and rate and amount of consolidation in soils that support the foundation. This is applicable to bridge foundation
Test to measure the supporting power of disturbed soils as compacted under standard procedures. The California Bearing Ratio Method(CBR)- combines a load deformation test performed in the laboratory with an empirical design chart to determine the thickness of pavement base and other layers.
The HVEEM Stabilometer Method- this method measures the horizontal pressure developed in a short cylindrical sample loaded vertical on its end. Stabilometer Test- after the expansion test is completed, the specimen is enclosed in a flexible sleeve and placed in the stabilometer. Vertical pressure is applied slowly at a speed of 0.05 in./min. until it reaches 160 psi. The developed horizontal pressure is reduced to 5 psi using the displacement pump. Then the turns of the displacement , pump needed to bring the horizontal pressure to 100 psi are determined, this displacement procedure is intended to measure the penetration of the flexible diagram into intersection of the sample. Triaxial Design Method- This method is adopted by some agencies for compression tests (see AASHTO desig. T 234) the open system triaxial test, lateral pressure is held constant by releasing from the container as increased load causes the sample to expand laterally.Nuclear Devices Test- recently, nuclear devices for determining in-place densities and moisture contents are used. The principle of the measurement by nuclear instrument is relatively simple. Gauge reading are easily converted to density and prevent moisture using calibration curves or microprocessors. The portable devices are of either the transmission or backscatter types. Soil Surveys A preliminary soil investigation is an integral part of highways reconnaissance and preliminary location survey.In fixing the position of the road the following has to be considered:Soil conditionsDirectness of routeTopographyRight of wayNeighborhood disruptionEnvironmental consideration The early phase of the soil survey is the collection of information such as:
Identification of soil types from geological and agricultural soil maps, aerial photographs and other sources.Investigation of ground water conditions.Examination of existing roadways cuts and other excavation.Review of the design and construction proceduresPresent condition of roads that traverse the area.Soil exploration along the right of way using auger boring and test pile.Sampling should be at frequent enough intervals to fix the boundaries of each soil types.
Test holes should extend to a significant depth below the sub grade elevation with a recommended minimum depth of 1.50 meters.A complete and systematic record shall be made for each hole.The location , the nature of the ground, origin of parent material, landform and agricultural soil name should be recorded.Each soil layer is described according to its thickness texture structure, organic, relation content and of cementation.The depth of seepage zones of the free water table and bedrock are also recorded.The soil profile along the roadway centerline showing location or test holes range of soil profile characteristic for each district soil type is plotted. Most highway agencies make a detailed study along with the first survey such as:The vertical and horizontal location of the proposed construction.Location and evaluation of suitable borrow and construction materials.Need for and type or sub grade or embankment foundation treatment and drainage.Need for special excavation and dewatering techniques.Development of detailed subsurface investigation for specific structure.Investigation of slope stability in both outs and embankment.Selection of roadway pavement type of section.