Geotechnical Engineering Properties of Soils Tests

Keywords: spt test, spt test analysis, engineering properties of soil, engineering soil tests

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Advantages and Disadvantages of SPT Standard Penetration Test

Advantages and Disadvantages of Cone Penetration Test

Advantages and Disadvantages of Shear Vane Test

Advantages and Disadvantages of Wash Boring

Advantages and Disadvantages of Percussion Rig Boring

Advantages and Disadvantages of Rotary Auger Boring

During the SPT, it was possible to take disturbed and undisturbed samples using split barrel-sampler that have been used for further laboratory tests. The in situ penetration test provides a soil sample for identification purposes as well as for the laboratory tests that allow the use of disturbed samples. The method of sampling soil contains driving a split-barrel sampler to secure a representative, disturbed sample and simultaneously get yourself a way of measuring the resistance of the subsoil to the penetration of a standard sampler. The test is conducted inside a borehole. A 'split spoon' sampler is attached to the bottom of the core barrel and lowered into position at the bottom of the borehole. The sampler is driven into the ground by the drop hammer weighing 68 kg falling through the height of 76 cm. The number of hammer blows is counted. The quantity required to drive the sampler three successive 150mm increments is recorded. The first increment (0-150mm) is not included in the N value as it is assumed that the most notable of the test area has been disturbed by the drilling process. The SPT N is the amount of blows necessary to achieve penetration from 150-450mm. The hammer weight, drop height, spoon diameter, rope diameter etc. are standard dimensions. Following the test, the sample remaining inside the split spoon is preserved in an airtight container for inspection and description.

Advantages and Disadvantages of SPT Standard Penetration Test

ADVANTAGES

  • Relatively quick and simple to perform
  • Able to penetrate dense layers, gravel, and fill
  • Equipment and expertise for the test is widely available
  • 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
  • Provides a representative soil sample
  • Provides useful index of relative strength and compressibility of the soil

DISADVANTAGES

  • The SPT does not typically provide continuous data, therefore important data such as weak seams may be missed
  • Somewhat slower than other sample methods due to sample retrieval
  • The basic problems to consider are change in effective stress in the bottom of the borehole, dynamic energy achieving the sampler, sampler design, interval of impact, penetration resistance count.
  • Samples that are extracted from the SPT are disturbed.

Cone Penetration Test (CPT)

What is CPT?

Cone Penetration Tests are conducted to get the cone resistance, the side friction and, when there is a piezocone, the pore pressure. The soil type can be dependant on analysing these result the values can be used in the look of shallow foundations through the estimation of stiffness and shear strength of cohesive soils. The cone penetration test (CPT) is a way used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to research soft soils. Based on this history it has also been called the "Dutch cone test". Today, the CPT is one of the most used and accepted in soil options for soil investigation worldwide.

Process

CPT is static penetration test in which the device is pushed rather than then driven by blows in to the soil. The CPT consist of cone which been attached to a rod that been protected by an outer sleeve. A 60o cone with face area 10cm2 and 150cm2 of friction sleeve is hydraulically pushed in to the ground at a frequent speed ranging from 1. 5 to 2. 5 cm/s about 80mm deep. The force required maintaining this penetration rate, and the shear force acting on the friction sleeve is recorded. The friction ratio gives an indication of the soil type. The CPT Soil Classification depends on ratio of tip and sleeve resistance. The end resistance will be high in sand and low in clays while the sleeve friction will be lower in sands and saturated in clays.

Advantages and Disadvantages of Cone Penetration Test

ADVANTAGE

  • Continuous data
  • Reliable, repeatable test results

DISADVANTAGES

  • Inability to penetrate through gravels and cobbles
  • Elimination of operator error
  • Less populated database than SPT due to the new technology
  • Lack of sampling

SHEAR VANE TEST

What is Shear Vane Test?

The vane shear test can be an in-situ geotechnical testing methods used to estimate the undrained shear strength of fully saturated clays without disturbance. The test is relatively simple, quick, and provides a cost-effective way of estimating the soil shear strength; therefore, it is trusted in geotechnical investigations. Under special condition, the vane shear test can be also completed in the laboratory on undisturbed soil specimens however the use of the vane shear test in in-situ testing is a lot more prevalent.

Process

The vane shear test is an in-situ geotechnical testing methods used to estimate the undrained shear strength of fully saturated clays without disturbance. The results of the test aren't reliable if clay contains silt or sand. The vane shear test apparatus consists of a four-blade stainless vane attached to a steel rod that will be pushed into the ground. For any weak soils which has Cu less than 50 kPa, the size of the blade is 75mm wide x 150 mm long while for the slightly strong soils which has Cu between 50 kPa to 100 kPa, 50 x 100 mm blade should be use. The height of vane is usually twice its overall widths and it is often add up to 10 cm or 15 cm.

The test can be conducted either from the bottom surface or from the bottom of your borehole or a test pit. If conducted from the bottom of your borehole, the test area should be should be at the depth of least three times the borehole diameter lower that the borehole bottom in order to avoid the borehole disturbance effects. The test starts by pushing the vane and the rod vertically into the soft soil. The vane is then rotated at a slow rate of 6 to 12 each and every minute. The torque is measured at regular time intervals and the test continues until a maximum torque is reached and the vane rotates rapidly for a number of revolutions. At this time, the soil fails in shear on the cylindrical surface across the vane. The rotation is usually continued after shearing and the torque is measured to estimate the remoulded shear strength. The undrained shear strength of the saturated soil is proportional to the applied torque and the dimensions of the vane.

Advantages and Disadvantages of Shear Vane Test

ADVANTAGES

  • Rapid and economical test
  • Reproducible results homogeneous soils
  • Inexpensive way for measuring clay sensitivity

DISADVANTAGES

  • Limited to soft to stiff cohesive soils
  • Field vane shear strength must be corrected
  • Results can be afflicted by anisotropic soils, sand lenses, shells, and seams

BORING

WASH BORING

What is Wash Boring?

A popular solution to drill larger size holes in soft formations. Casing with a casing crown attached is rotated into the ground and water can be used to flush out the drilled formation. It really is one of your boring system where material loosened by a little is borne to the surface in the annular space between the bit and casing by water forced down through the pipe bearing the bit

Process

For test boring over 3 meter comprehensive, this method can be conveniently used. In this method a hollow steel pipe known as casing pipe or drive pipe is driven into the ground for a certain depth. A pipe usually known as water jet pipe or wash pipe, which is shorter in diameter, is lowered in to the casing pipe. At its upper end, the wash pipe is linked to water supply system as the lower end of the pipe is contracted in order to produce jet action.

Water under considerable pressure is forced down the wash pipe. The hydraulic pressure displaces the material immediately below the pipe and the slurry thus formed is forced up through the annular space between the two pipes. The slurry is collected and samples of material encountered are obtained by settlement. In this technique the particles of finer material like clay, loam etc. do not settle easily and the larger and heavy particles of the soil might not be brought up whatsoever.

Moreover, the exact position of the material in the formation cannot be easily be located. Nevertheless the change of stratification can be guessed from the speed of progress of driving the casing pipe as well as the colour of slurry flowing out. The results obtained by wash boring process give fairly good information about the nature of the sub-soil strata. This technique can be adopted in soft to stiff cohesive soils and mud.

Advantages and Disadvantages of Wash Boring

ADVANTAGES

  • Can be used in difficult terrain
  • Low equipment cost
  • Used in uncased holes

DISADVANTAGES

  • Depth limited to about 30m
  • Difficulty in obtaining accurate location of groundwater level.
  • Undisturbed soil samples can't be obtained.

PERCUSSION RIG BORING

What is Percussion Rig Boring?

Percussion Rug Boring is trusted in UK. Percussion drilling approach to advancing a boring is of common used in drilling water wells. This technique consists of splitting up of the sub-strata by repeated blows from somewhat or chisel. This sort of boring can make a borehole up to 150 mm - 300 mm diameter and depth up to 50 - 60 m. However this technique is not recommended for loose sand or clayey soils.

Process

This method includes splitting up of the sub-strata by repeated blows from a bit or chisel. Percussion methods begin by raise the tool assembly by the winch to at least one 1 m above the bottom of the hole. It allows the tool assembly to fall under its own weight to drive the cutting tools in to the soil. The material thus pulverized is converted into slurry by pouring water in the bore. At intervals the slurry is bailed from the hole and dried for examination.

The slurry will be removed by bailers or pump. From then on, tool will be raise to surface when the cutting tools are full of soil to acquire undisturbed sample. This technique can be adopted in rocks and soils having boulders. Generally, a machine used to drill holes is named a drill rig generally power driven, but may be hand driven. A winch is provided to improve and lower the drilling tools into the hole.

Advantages and Disadvantages of Percussion Rig Boring

ADVANTAGES

  • Simple to use and maintain
  • Suitable for a wide variety of rocks
  • Operation can be done above and below the water-table
  • It can be done to drill to considerable depths

DISADVANTAGES

  • Slow, weighed against other methods
  • Equipment can be heavy
  • Problems can occur with unstable rock formations
  • Water is necessary for dry holes to help remove cuttings

ROTARY AUGER BORING

What is Rotary Auger Boring?

A drill bit is pushed by weight of drilling equipment and rotated by way of a motor. This drilling method with mud pump for flushing can be direct circulation and reverse circulation, with tricone bit and drag bit Nevertheless, the torque is relatively crucial for this drilling method. It is trusted in soft to medium hard ground conditions. This type of boring machine can be also use for piling works. It can bore the hole up to depth of 50 m and diameter of 300 mm to 2 m.

Process

When rocks or hard pans are to be penetrated for examination, core drilling is performed to get undisturbed samples of the formation. In this process a hole is made by rotating a hollow steel tube developing a cutting bit at its base. The cutting bit makes an annular cut in the strata and leaves a cylindrical core of the material in the hollow tube. Two types of cutting bits are generally used, namely, diamonds bit and shot bit. Diamond bit contains industrial diamonds occur the face of the bit and in shot bit, chilled shot can be used as an abrasive to slice the hard pan. When core samples of small diameter are needed, diamond bit is recommended. You can find two main kind of rotary auger boring that happen to be:

Bucket Auger

  • Consists of an open-top metal cylinder with cutter installed on a baseplate as the soil is cut, it passes in to the bucket, which is then raised and emptied at intervals.
  • Can be used in frim soil.
  • Not well suited for cohesionless soil below water table.
  • Flight Auger
  • Short flight
  • Simple flight
  • Continuous flight

Advantages and Disadvantages of Rotary Auger Boring

ADVANTAGE

  • Quick
  • Drill through any kind of soil or rock
  • Can drill to depths of 50 m
  • Undisturbed samples can be easily recovered

DISADVANTAGE

  • Expensive equipment
  • Terrain must be accessible to motorized vehicle
  • Difficulty in obtaining location of groundwater level
  • Additional time necessary for set-up and clean-up
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