The SPTMAN is an easy to use and portable system that is used to calculate SPT hammer energy.
The SPTMAN system measures the actual energy transferred from the SPT hammer to the drive rods and calculates the hammer energy coefficient by comparison with the theoretical potential energy.
The heart of the system is a rugged, portable analyser with solid state memory. The system is usually supplied with a standard 54mm diameter 1m long instrumented SPT rod, as well as a waterproof carry case for added protection. Other instrumented rods can be supplied to order, such as AW, BW, NWY etc.
Tests are carried out using as easy to follow menu display which enables hammer energy and energy ration to be displayed in real-time. Further analysis and reporting is carried out using the SPTMAN PC software supplied as standard.
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SPTMAN hammer energy tester: Frequently asked questions
A: The SPT hammer energy measurement can be used to more accurately compare SPT hammer N values as the actual energy imparted by differ slightly from hammer to hammer.
A: This in practice is the measurement of the actual SPT hammer energy imparted to the top of the drill string and a comparison made with the theoretical energy for a standard SPT hammer to produce an SPT hammer energy ratio.
A: The energy ratio is the difference between the measured energy and the theoretical energy (473J). The measured energy will always be less due to friction and energy loss on impact. Typically for trip hammers the value is 60-70% and for window samplers 70-80%.
A: The standard weight of an SPT hammer (falling weight) is 63.5KG and the standard drop height is 760mm, and this should generate a theoretical energy of 473J.
A: Ideally between 10-12m to allow the energy to be gathered before the base echo, in a cased borehole and with a gravel plug at the base.
A: The energy of an SPT hammer is calculated by using an instrumented rod and measurement equipment (i.e. the SPTMAN system) to measure the acceleration and strains developed in the instrumented rod, and then by calculation deriving the energy produced – effectively a form of stress wave analysis similar to used in pile driving analysis.
A: BS EN ISO 22476-3 states the energy ratio of equipment carrying out Standard Penetration Tests has to be known “if N values are to be used for quantitative evaluation of foundations or for comparisons of results”.
A: The CPT method pushes a steel cone into the ground and uses an electronic measuring system to record tip resistance and sleeve friction. As the cone is pushed into the ground, the soil responds with differing degrees of resistance and the resistance is recorded using force sensors in the tip. The SPT method is probably the most frequently used method of subsurface drilling investigation testing, and measures the number of blows for a standard hammer to drive the sampler into the ground at set depths.
A: The number of blows required to penetrate the first 15 cm is called “seating drive” and the total number of blows required to penetrate the remaining 30 cm depth is known as the “standard penetration resistance”, or otherwise, the “N-value”.
A: Typically once the hammer is set up on the test drill string, about 15-20 minutes.
A: It is recommended that measurements are carried out annually, unless equipment has been modified or damaged, or as requested by the client. It is often the case that where multiple rigs are required on large contracts, SPT equipment to be used are calibrated at the start.
The measurement of SPT hammer energy is now recommended for all Standard Penetrometer Test (SPT) systems.
BS EN ISO 22476-3 states that the hammer energy ratio has to be known and have a certificate of calibration available if N values are going to be used for the quantitative evaluation of foundations or for the comparison of results.
This standard also recommends that checks should be carried out on a six monthly basis. We recommend that it is also good practice to carry out a calibration at the start of any large contract.
Benefits of the SPTMAN hammer energy tester:
- Instant hammer energy measurement and transfer coefficient calculation
- Rugged and lightweight system
- Storage for over 700 results
- Complies with the relevant parts of both BS EN ISO 22476-3 and ASTM D 4633-10
- Backlit LCD screen for working in dark environments
- Calibration service available
| All of our equipment is supplied fully calibrated to UK national standards. | |
|---|---|
| SPTMAN unit | |
| Features | On-site energymeasurement Standard energy check unit included for on-site verification Daylight viewable screen Rugged lightweight unit with waterproof connectors Tactile large keys for operating with gloves Low power with long battery life Flash memory for instant start up and power down |
| Keypad | Sealed colour coded andfull alphanumeric keypad, tactile and audio feedback |
| Operating temperature | 0 to +50°C |
| Display | Monochrome LCDtransflective with backlight Contrast keypad adjustable Display area 122mm x 77mm Protective anti-reflective glass |
| Acquisition | 2 channel, 16 bitacquisition at 100KHz sample rate Pre-trigger on both channels, auto ranging gain feature |
| Frequency range | 0Hz to 5000Hz |
| Storage | 700+ results, 3 datasets per pile with full header information including site, test no, dropheight, drop weight and date/time stamp |
| Display | Acceleration v time Force v time Energy measurement as % of theoretical |
| Accuracy | ± 2% of hammer energy |
| Power | Battery: 1.2V NiMHrechargeable AA cells Auto power off and battery indicator |
| Battery life | 8 hours + operation onfull charge |
| Charge time | Approx 6 hours |
| Charging | External wall plug-incharger for 100/110/250VAC inputs (trickle charge) External cigar plug-in charger for 12VDC inputs (fast charge) |
| Dimensions | L 218mm x W 187mm x D55mm |
| Weight | 1.35Kg |
| Instrumental rod | |
| Type | To suit clientsrequirements - normally BW/NW/AW |
| Length | Dependent on diameter -typically 1m |
| Accelerometers | 2No 10000g 'shock' typewith ICP power supply |
| Strain gauge type | Foil |
| Connection | 3m fly leads with ruggedbayonet connectors |
Lightweight modular reference beam:
- Manufactured from aluminium with zinc plated steel legs
- 3m in length – 0.5m short extension available
- Beam height adjustable to 3 positions
- Support bar for up to 4 displacement transducers
- Supplied in a rugged case
The SPTMAN analysis software is supplied as standard, and adapts a user friendly, Windows based platform for downloading data, analysing results and producing calibration certificates.
The certificate includes plots of force, velocity, acceleration and displacement; as well as measured energy, theoretical energy and energy ratio. Full details of the rig and site can also be shown.
The SPT hammer energy measurement method is based on the propagation of waves in long elastic cylinders. When the SPT rod is struck with a falling weight, the rod section is deformed (enlarged) and this enlargement travels down the pile to the base of the rod where it is reflected back.
The force transmitted to the rods is calculated by measuring the axial strain in the rod over a period of time and taking the modulus and cross section of the rod into account by:
F(t) = Aa x Ea x εm(t)
The particle velocity of the measurement section is determined by integrating data from the accelerometers over a period of time. The energy which passes into the drive rods can be determined from the force and velocity data using:
E(t’) = t∫0 F (t) v (t) dt
