SPT hammer SPT tube SPT shoe
Product profile: Automatic SPT Hammer
The Automatic Trip Hammer is manufactured to comply with the Standard Penetration Test (SPT) to BS 1377: Part 9: 1990. SPT Drive Rods and a Split Tube Sampler are connected to the base of the anvil, and driven into the ground by the falling weight.
The Automatic SPT Hammer comprises a weight of 63.5 kg complete with pick-up and self-tripping mechanism that ensures that the weight has a free-fall of exactly 760 mm. The inner shaft acts as a guide that permits the weight to drop with minimal resistance and ensures that the weight strikes the anvil squarely. The Anvil
thread is usually be processed with a 1-1/2" B.S. whitworth to fit our standard SPT rods.
Adaptors to other types of drill rod can be supplied on request.
The overall length of the hammer is 2.6 m extended and 1.8 m when unextended. The total weight of the hammer is 107 kg.
Terminology, symbols
2.1 Terminology
2.1.1 Standard Penetration Test
Use donut hammer weighing 63.5Kg to driven standard split barrel sampler in borehole bottom at falling distance 76cm for each hammer blow after a seating interval 15cm. Record the blow counts for 30cm penetration to study the soil physical and mechanical properties.
2.2 Symbols
N-Standard Penetration Test Hammer Blow Counts
N'-Revised Blow Counts after drill rods length variate is introduced
a-drill rods length revising coefficient
3.0.1 Testing Equipments
1. Split Barrel Sampler: consists of blade edged open shoe, split tube and head with vent.
2. Hammer Drop System: consists of donut hammer, anvil, guide tube and self tripping system
3. Drill Rods
Table: 3.0.1 SPT Equipment specs and precision
| Equipment |
Specs |
Precision |
| Split Barrel Sampler |
Split Tube |
O.D. 51mm
I. D. 35mm |
+/- 1mm
+/- 1mm
Roughness 3.2
Ellipticity 0.08mm
Concentricity 0.05mm |
| Length >500mm |
- |
| Open Shoe |
Length 50-76mm
Blade Edge Thickness: 2.5mm
Blade taper: 18°-20° |
- |
| Donut Hammer |
Weight 63.5kg |
+/-0.5kg |
| Guiding Tube |
Falling Distance 76cm |
+/-2cm |
| Drill Rods |
Diameter 42mm |
Bending allowance,<=1/1000 |
4. Testing Method
4.1.1 Borehole shall conform to the following requirement:
1. Shall employ rotate drilling, the perpendicularity shall meet the specification of drilling standard. Borehole diameter is suitable to be 76-150mm.
2. Drilling shall be stopped when reach to 15cm above the desired tested level and remove residual in the borehole bottom, residual soil thickness shall not exceed 5cm. Be careful for not disturb the soil under borehole bottom during cleaning process.
3. When test is carried out under the underground water soil level, make sure the water level in borehole is higher than underground water level; when the borehole wall is not stable, mud protection or casing pipe protection shall be introduced; if use casing pipes, must not push the pipe to the testing depth.
4.2 Testing Procedure
4.2.2 Pre-penetrate 15cm(including the penetration length by the gravity of the equipments), and then start the formal testing.
4.2.3 Lift the hammer to the given height, and make it falling down automatically, free fall and hit. Hammer speed shall not exceed 30 times/min. record the blow counts for every 10cm penetration. The hammer blow counts for total 30cm penetration is recorded as standard penetration hammer blow counts(SPT) N.
4.2.4 If the penetration can not reach 30cm after 50 hammer blow, the test can be stopped and record the actual penetration length. And calculate N according to the formula(4.2.5) as specified in this standard.
4.2.5 If in a 30cm penetration has different soil stratum, can calculate N as per the formula(4.2.5) based on the blow counts and penetration distance in each soil stratum.
N=30n/Δs (4.2.5)
Amid, Δs-actual penetration depth
n-blow counts for penetrate Δs
4.2.6 The test shall not be stopped in every given depth. If stop is happened, shall note the reason and the time stopped.
4.2.7 After penetration testing, shall open split tube and shall review and describe the soil samples, and shall take disturbed soil sample as per requirement.
5. Documentation
5.0.4 If drill rods length revision is needed, and the total length not exceed 21meters, the revision can be performed as per the formula(5.0.4)
N'=a.N (5.0.4)
Amid, N'- Revised SPT hammer blow counts
a-drill rods revision coefficient, value as per the table 5.0.4
Table 5.0.4 Drill Rod Revision Coefficient a
| Drill Rods Length(m) |
≤3 |
6 |
9 |
12 |
15 |
18 |
21 |
| a |
1.00 |
0.92 |
0.86 |
0.71 |
0.77 |
0.73 |
0.70 |
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