Standard penetration test

SOIL EXPLORATION : 

SOIL EXPLORATION NAME- ISHA BRANCH- CIVIL(3 rd year) ROLL NO-0909025

Standard penetration test: 

Standard penetration test It is a common situ testing method used to determine the geotechnical properties of subsurface soil test is used to estimate the relative density of soils and approximate shear strength parameters.

General equipments:-: 

General equipments:- SPLIT-SPOON SAMPLER HAMMER ROTATION OF ROPE AROUND A CATHEAD

SPLIT SPOON SAMPLER: 

SPLIT SPOON SAMPLER

HAMMER: 

HAMMER

DONUT HAMMER: 

DONUT HAMMER Open system Delivers approximately 45% of the maximum free-fall energy Highly variable energy transfer

SAFETY HAMMER: 

SAFETY HAMMER Closed system Delivers approximately 60% of the maximum free fall energy Highly variable energy transfer

AUTOMATIC HAMMER: 

AUTOMATIC HAMMER Safest system Delivers approximately 95-100% of the maximum free fall energy Consistent and effective energy transfer Increased production

PROCEDURE: 

PROCEDURE It involves driving a standard thick-walled sample tube into the ground at the bottom of a borehole by blows from a slide hammer with standard weight and falling distance The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded . The sum of the number of blows required for the second and third 6 in. of penetration is reported as SPT blowcount value SPT blowcount value is commonly termed  "standard penetration resistance" or the "N-value ". The N-value provides an indication of the relative density of the subsurface soil, and it is used in empirical geotechnical correlation to estimate the approximate shear strength properties of the soils.

ADVANTAGES OF SPT: 

ADVANTAGES OF SPT Relatively quick and simple to perform ‹ One procedure ‹ Equipment and expertise for the test is widely available in the United States. ‹ Provides a representative soil sample. ‹ Provides useful index of relative strength and compressibility of the soil. ‹ Able to penetrate dense layers, gravel, and fill ‹ Numerous case histories of soil liquefaction during past earthquakes are available with SPT N-values. The method based on this history can reflect actual soil behaviour during earthquakes, which cannot be simulated in the laboratory. ‹ The SPT is an in situ test that reflects soil density, soil fabric, stress and strain history effects, and horizontal effective stress, all of which are known to influence the liquefaction resistance but are difficult to obtain with undisturbed samples.

DISADVANTAGES OF SPT: 

DISADVANTAGES OF SPT The SPT does not typically provide continuous data (e.g. 5 ft. intervals), therefore important data such as weak seams may be missed. Limited applicability to cohesive soils, gravels, cobbles boulders Equipment and expertise for the test is widely available in the United States. ‹ Somewhat slower than other sample methods due to sample retrieval. ‹ In addition to overburden pressure and relative density the SPT N-value is also a function of soil type, particle size, and age and stress history of the deposit ‹ Due to considerable differences in apparatus and procedure, significant variability of measured penetration resistance can occur. The basic problems to consider are change in effective stress at the bottom of the borehole, dynamic energy reaching the sampler, sampler design, interval of impact, penetration resistance count. ‹ Samples that are obtained from the SPT are disturbed.

STATIC CONE PENETRATION TEST: 

STATIC CONE PENETRATION TEST Static cone penetration test is internationally recognized as a standard field test to collect data about bearing capacity and frictional resistance of soil The standardized cone-penetrometer test (CPT) involves pushing a 1.41-inch diameter 55 º to 60 º cone through the underlying ground at a rate of 1 to 2 cm/sec. CPT soundings can be very effective in site characterization, especially sites with discrete stratigraphic horizons or discontinuous lenses.

Types of cones: 

Types of cones

PROCEDURE : 

PROCEDURE A CPT sounding is made by pushing a small probe into the ground. a 3.6-centimeter-diameter probe (cone) is pushed into the ground to depths ranging from 15 to 30 meters. The cone is advanced downward at a constant velocity of 2 centimeters per second, using hydraulic rams that apply the full 23-ton weight of the CPT truck to push the probe rods to depth. resistance to penetration of the tip and the frictional sliding resistance of the sleeve of the cone are measured continuously. Soil type is inferred from a chart that compares these two measurements with the known physical properties of various soils .

VARIOUS SENSORS & TOOLS: 

VARIOUS SENSORS & TOOLS electrical-resistivity modules, temperature and volatile-organic-compound (VOC) sensors, ground-water, soil, and discrete-gas samplers, seismometers, in-place vane shear, and video imaging.

ADVANTAGES OF CPT: 

ADVANTAGES OF CPT • Rapid data acquisition • No drilling mess • Immediate data availability • Detailed subsurface information

CAPABILITIES: 

CAPABILITIES • Shear-wave-velocity measurement • Detailed stratigraphic profiling • Soil sampling • Pore-fluid-pressure/water-table measurement • Evaluation of liquefaction potential • Vane-shear measurement • Video imagery • Vertical temperature profiling • Direct-push sensor installation • Ground-water sampling • Monitoring wells • Conductivity/resistivity measurements • Ground-penetrating radar • Discrete-gas sampling • Regional and site-specific stratigraphy • Laser-induced fluorescence • Volatile-organic-compound sensing

APPLICATIONS: 

APPLICATIONS • Seismic-hazard mapping • Paleoseismic exploration • Ground-water-quality studies • Environmental-contamination studies • Regional or site-specific three-dimensional mapping of shallow sedimentary deposits