\STANDARD PENETRATION TEST SPT

\STANDARD PENETRATION TEST SPT

\STANDARD PENETRATION TEST SPT

25/05/2021

The Standard Penetration Test, also known as the SPT (Standard Penetration Test) test, has been around since 1927 and is probably the most commonly used test method for determining geotechnical properties. art of the land.

NATIONAL STANDARDS

TCVN 9351:2012

CONSTRUCTION LAND - STANDARD TESTING METHODS - STANDARD PERFORMANCE TEST (SPT)

Soils - Field testing method - Standard penetration test

Preface

   TCVN 9351:2012 is converted from TCXD 226:1999 according to the provisions of Clause 1, Article 69 of the Law on Standards and Technical Regulations and point a, Clause 1, Article 7 of Decree No. 127/2007/ND-CP dated August 1 2007 of the Government detailing the implementation of a number of articles of the Law on Standards and Technical Regulations.

   TCVN 9351:2012 compiled by the Institute of Construction Science and Technology - Ministry of Construction, proposed by the Ministry of Construction, appraised by the General Department of Standards, Metrology and Quality, and published by the Ministry of Science and Technology.

1. Scope of application

   1.1 This International Standard specifies a method for determining the penetration resistance of soil at the bottom of a borehole when penetrating a sample pipe by hammering according to the standard and taking destructive samples for classification tests.

   1.2 This International Standard is mainly used to evaluate the strength and strain parameters of loose soils, however some valuable data can be obtained in other soils.

   1.3 This standard includes regulations on experimental equipment and methods when conducting geological surveys. Interpretation, evaluation and use of experimental results for foundation calculations can be found in the appendices.

2. References

   The following referenced documents are necessary for the application of this standard. For dated references, the version stated applies. For undated referenced documents, the latest version, including amendments and supplements (if any), applies.

   TCVN 4419:1987, Construction survey - Basic principles.

   TCVN 9363:2012, High-rise buildings - Geotechnical investigation.

3. Terms and definitions

   The following terms and definitions are used in this standard:

3.1. Standard Penetration Test (SPT)

   One of the methods of engineering geological survey for the construction of different works. The test is carried out by driving a sample tubular piercing into the soil from the bottom of a well constructed borehole suitable for the test. The piercing specification, equipment and closing energy are specified. The number of hammers required to drive the tip into the soil at specified depth intervals is recorded and corrected. The soil contained in the sample tube is observed, described, preserved and tested as a disturbed soil sample.

3.2. Standard Penetration resistance, N spt

   The number of hammers required to drive the tip into the intact soil is 30 cm with the equipment specifications and test methods specified in Articles 5 and 6.

4. General provisions

   4.1 SPT test should be used when surveying engineering geology in complex stratigraphic conditions, alternately distributed cohesive and loose soil layers or consisting mainly of loose soil layers with compaction, grain composition different.

   4.2 The specific volume of the SPT experiment and the correlation between the SPT and other survey methods during the survey are determined according to the provisions of TCVN 4419:1987 and TCVN 9363:2012 or other relevant standards. .

   4.3 SPT tests must be performed by qualified technicians and test results must also be interpreted and evaluated by experienced professionals.

5. Experimental equipment

   5.1 A set of SPT test equipment includes the following basic parts:

- Hole drilling equipment tạo

- Piercing head

- Hammer set

   5.2 Drilling equipment used to create test holes. Any machine and drilling method can be used as long as the borehole meets the technical requirements for diameter, the wall is stable, ensures maximum integrity of the soil at the bottom of the borehole and reaches a depth required for the experiment.

   5.2.1 The borehole diameter should be between 55 mm and 163 mm.

   5.2.2 The most suitable drill rod for the test is the one with an outer diameter of 42 mm and a weight of 5.7 kg/m.

   5.3 The piercing head is a steel pipe with a total length of up to 810 mm, consisting of three parts: the nose part, the body part, the connector part and are connected by thread. Specific specifications:

- Outer diameter: (51.0 ± 1.5) mm;

- Inner diameter: (38.0 ± 1.5) mm.

ANNOUNCEMENT

1 piercing

2 Connector part

3 Body Parts

4 marbles

   5.3.1 The penetrator is the bottom part of the tip used for cutting when penetrating the soil. The basic characteristics of the piercing nose are as follows:

- Length from 25.0 mm to 75.0 mm;

- The inner diameter is equal to (35.0 ± 0.15)mm;

- The blade thickness is equal to (2,5 ± 0.25) mm;

- Blade chamfer angle from 16.0° to 23.0°.

   5.3.2 The body of the penetrometer from 450 mm to 750 mm long is used to store the soil and the air to penetrate the soil. The body consists of two halves of a semicircle, which is convenient for disassembly when taking out the soil contained in them. The two ends of the body tube have external threads for assembly with the nose and the connector.

   5.3.3 The terminal part of the bushing, for connecting the bushing to the drill rod, up to 175 mm in length. Here, there is a ball mechanism, a steam hole to keep the vacuum inside the piercing head, limit the sample drop during the lifting and lowering of the piercing nose and to release steam and water during the piercing process.

   5.4 Hammer set used to generate power to drive the nose into the ground, including: hammer, hammer picker and guide rod.

   5.4.1 Rotating cylindrical steel hammer with a central hole to allow it to slide freely along the guide. The hammer must be of a suitable construction with the release gripper, so that it can be easily picked up and released from the required height.

- Hammer weight: (63.5 ± 1.0) kg;

- Height of free fall: (76.0 ± 2.5) cm

NOTES:

1 Guide bar

2 sets of tongs

3 Dumbbells: (63.5 ± 1.0) kg

4 anvil

Figure 2 - Hammer set

   5.4.2 The gripper is a part used to raise and lower the hammer automatically and in accordance with regulations, ensuring the hammer falls freely, limiting energy consumption during the fall.

   5.4.3 Guide rod to direct the drop of hammer, consisting of anvil and guide bar. The anvil is a steel base that receives the energy of the hammer drop and transmits it to the penetration through the drill rod system. The guide bar has a diameter suitable for the diameter of the middle hole of the hammer and has a special structure that helps the gripper release the hammer at the right time, reaching the specified drop height.

   5.4.4 Other auxiliary tools are also needed during the experiment. It is sample box, ruler, chalk, nylon bag, record, water level measuring device...

6. Experimental method

   6.1 The SPT experiment includes the following tasks in turn at each test site:

a) Drill holes to the depth to be tested and clean the bottom of the borehole;

b) Conduct experiments;

c) Observe and describe.

   The above work is continued in the next depths. The experiment was carried out at 1 m to 3 m in turn until the required depth depending on the purpose of the survey and the complexity of the stratigraphy.

   6.2 When drilling holes, the following drilling methods can be applied:

- Drill twist reel;

- Rotary drilling with water washing with water or clay solution.

   To avoid collapsing the borehole wall, when necessary, anti-wall pipes can be used.

   Drill holes must be in position, vertical, large enough diameter from 55 mm to 163 mm. The borehole wall must be stable and minimize damage to the soil at the bottom of the borehole.

   6.2.1 When drilling at a low depth, above the groundwater level, twist drills should be used. Using a support pipe, if there is weak ground, the soil is not tightly structured to avoid collapsing the borehole wall.

   6.2.2 When drilling below the groundwater level, rotary drilling should be used with water washing with water in cohesive soil and with washing water with clay solution in loose soil.

   6.2.3 During the drilling process, it is necessary to regularly monitor the drilling speed, the characteristics of the drilling fluid in order to promptly recognize the stratigraphic changes and make a reasonable decision on the experimental depth. The drilling fluid level should always be above the groundwater level.

   6.2.4 When drilling close to the test depth, it is recommended to reduce the drilling speed, gently lift and lower to minimize damage to the integrity of the soil at the bottom of the borehole, and distort the test results. .

   6.2.5 When drilling to the experimental depth, dredge the bottom of the borehole, check the depth and stability of the borehole wall. When necessary, the bottom of the borehole can be washed and cleaned by recirculating the drilling fluid.

   6.2.6 When the borehole is deep enough, the bottom is clean, and the wall is stable, pull out the drill bit and replace it with a piercing tip.

   6.3 The test begins when the penetration has reached the bottom of the borehole, to the required depth, without any obstruction due to wall collapse. The experiment was conducted as follows:

   6.3.1 Install the hammer set and check the hammer's ability to release and release, the free fall height of the hammer. The guide bar must be vertical, stable and coaxial with the boom system.

   6.3.2 Select a reference point and measure on the drill rod three consecutive segments, each 15 cm long, for a total of 45 cm above the reference point, based on which the penetration resistance is determined.

   6.3.3 Close the hammer. Pay attention to the drop height of the hammer, the verticality of the guide bar.

   6.3.4 Count and record the number of hammers required to penetrate the soil at each 15 cm segment outlined on the drill rod.

   6.3.5 When the number of hammers required for 15 cm exceeds fifty hammers (or one hundred hammers depending on the requirements of the survey design), measure and record the penetration depth, in centimeters (cm) of the penetration. at fifty hammers (or one hundred hammers).

   6.3.6 In coarse-grained sandy soil mixed with grit or gravel and gravel, in order to avoid damage to the piercing tip, it is recommended to use a cone-shaped solid penetrator of the same size as an alternative to a regular piercing. The tip angle of the nose piercing cone is 60°.

   6.3.7 During closing, the water level or drilling fluid should be above the existing groundwater level.

   6.3.8 After measuring and recording the number of hammers corresponding to the 45 cm penetration depth of the penetration, proceed to cut the ground by rotating the drill rod, withdrawing the penetration to the ground, and replacing it with the drill bit. Drilling continued to new depths.

   6.4 The piercing tip is removed from the drill rod, washed and disassembled into three parts. Split the body of the piercing tip in half, observe and describe the soil contained therein. Reassemble the tip ready for testing at the new depth.

   6.4.1 Soil contained in the tip body is observed, described and compared with the soil contained in the nose. Clearly describe the color, moisture, density, grain composition, architecture, texture of the soil, foreign bodies...

   6.4.2 Select a representative sample and store it in a nylon bag that is impervious to water, vapor and gas. Each sample must have a label clearly stating the project name, borehole number, sampling depth, number of hammers for three penetration ranges, testing time, and weather characteristics.

   6.4.3 Sample bags are arranged in order of depth for easy observation and inspection, kept in a cool place and transported immediately to the laboratory.

   6.4.4 Soil obtained in the penetrator may be used for laboratory testing to determine a number of physical properties for identification and classification purposes. Detail:

- Humidity;

- Mass and volume of seeds;

- Grain composition;

- Humidity limits.

   6.4.5 Soil samples taken from the tip must be preserved and stored in the laboratory for at least three months from the date of acceptance of the test results.

7. Correction and interpretation of results

   7.1 SPT test results obtained from the field are adjusted for each borehole.

   7.2 At each test depth, calculate the penetration resistance SPT (N spt ); N spt  is the total number of hammers at the last 30 cm of the piercing tip.

   7.3 On the basis of documents describing the soil in the field, the value of SPT penetration resistance, laboratory test documents on the obtained soil sample, stratification of the borehole stratigraphic division, and record of the test results , plot penetration resistance value against depth. For the test results, please refer to Appendix B.

   7.4 SPT test results are used for the following purposes:

   7.4.1 Stratigraphic division, detection of clamping layers, loose-grained soil lenses, distinguishing loose-grained soils with different compaction by area and by depth.

   7.4.2 Evaluation of the value of some physical and mechanical parameters such as:

- Tightness, internal friction angle of loose grain soil;

- Viscosity, compressive strength with expansion of cohesive soil;

- Deformation modulus of loose soil;

- Static penetration resistance of the soil.

   7.4.3 Evaluation of some soil dynamic criteria such as:

- Dilution capacity of loose soil;

- Speed ​​of waves in the ground.

   7.4.4 Forecast of load carrying capacity of some types of foundation:

- Load carrying capacity of shallow foundation on loose soil;

- Load carrying capacity of piles, mainly supporting piles, especially bored piles.

Relationship between standard penetration resistance N spt  and tip static penetration resistance q c

 

     Table 1- Relationship between standard penetration resistance N spt  and tip static penetration resistance q c

Order

Soil type

Ratio q c /N spt

first

Lighting

2

2

Lightning

3

3

Fine-grained sand

4

4

Medium grain sand, coarse

From 5 to 6

5

Medium grain sand and gravel

Greater than 8

Evaluation of the value of some physical and mechanical parameters of the soil according to the results of SPT

1. For loose land

   The following properties of loose soil can be evaluated according to SPT test results:

- Relative density, D r ;

- Angle of internal friction, j;

- Deformation modulus, E.

1.1 Relative compaction (D r ) and internal friction angle (j)

 Table 2 - Relationship N 30  and D r , j

 (According to Terzaghi, Peck)

Status

r  (%)

spt

j(°)

Styrofoam

Less than 30

Less than 10

From 25.00 to 30.00

Medium cut

From 30 to 60

From 10 to 30

From 30.00 to 32.30

Chop

From 60 to 80

From 30 to 50

From 32.30 to 40.00

Very tight

More than 80

More than 50

From 40.00 to 45.00

 

   Self-pressure or depth and position of the soil also affect this relationship. The graph of the relationship between N spt  and D r  includes this factor. Accordingly, the values ​​shown in Table 2 correspond to the self-pressure of 0.144 MPa.

   The relationship between internal friction angle and standard penetration resistance can be as follows: (According to Terzaghi, Peck, Meyerthof...)

Inside:

a is the coefficient, taking the value between 15 and 25

1.2 Strain modulus E, in Megapascan (MPa)

(According to Tassios, Anagnostopoulos)

Inside:

a is the coefficient, taken as 40 when N spt  >15; taken as 0 when N spt  < 15.

c is the coefficient, taken depending on the type of soil:

- c is taken as 3.0 for clay soils;

- take 3.5 with fine sandy soil;

- equal to 4.5 with medium sandy soil;

- taken as 7.0 with coarse sandy soil;

- equal to 10.0 with sandy soil mixed with gravel;

- taken as 12.0 with gravel and sand soil.

2. For sticky soil

   Table 2 - Relationship N spt , viscosity and compressive strength with hip expansion (q u )

spt

Viscosity

u , MPa

Less than 2

run

Less than 0.025

From 2 to 4

flexible - flowing -

From 0.025 to 0.050

From 4 to 8

flexible

From 0.050 to 0.100

From 8 to 10

hard

From 0.100 to 0.200

From 15 to 30

very hard

From 0.200 to 0.400

More than 30

snake

Greater than 0.400

   Calculating foundation according to SPT . results

1. Shallow foundation

   The allowable load carrying capacity of the ice foundation on loose grain soil can be calculated by the formula.

   (According to Tassios, Anagnostopoulos).

2. Pile foundation

   The general formula for calculating the allowable load carrying capacity of the pile foundation according to the SPT results can be obtained at the request of the Japanese Ministry of Construction.

TCVN 9351:2012 Standard penetration test standard SPT

ASTM 1586 Standard Penetration Test

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