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DESCRIPTION

The VIBSIST-20 is based on the Swept Impact Seismic Technique (SIST) which is a combination of the Vibroseis swept-frequency and the Mini-Sosie multi-impact ideas. The seismic signals are produced as a series of pulses, according to a specific pre-programmed sequence which makes the system similar to a smaller Vibroseis.

The use of the monotonous variation of the impact rate controls effectively the non-repeatability of the impact intervals and achieves a wide bandwidth even when the coupling to the rock or ground is relatively poor.

Using standard construction equipment allows the VIBSIST-20 to become a safe, non-destructive and environmentally friendly high resolution seismic source. It also makes this seismic method reliable and highly cost effective.

APPLICATIONS

The VIBSIST-20 can be used in a wide range of applications, they include:

• tunnel investigations

• depth to bedrock

• ground water exploration

• location of fractured zones

• foundation studies

• placer exploration

• gravel detection

• shear and surface wave studies

• static correction surveys

• VSP measurements

• research and education

MAJOR BENEFITS

EXCELLENT SOURCE FOR HIGH RESOLUTION SEISMIC SURVEYS

The VIBSIST-20 is an excellent reflection/refraction source because it obtains equivalent depth or better than would small caps explosive or single pulse sources while maintaining a higher resolution and an increased productivity.

The high S/N Ratio is achieved by a signal energy of 10 kJ over a period of 25 seconds or the equivalent of 22 impacts per second. It is the accumulation of these low energy impacts which leads to significant depth penetration.

INCREASED PRODUCTIVITY

Significant productivity gains are obtained because the VIBSIST-20 hand-held electromechanical hammer is not dependent on the energy of the operator using a sledgehammer or on the lengthy preparation needed to use explosives, such as drilling holes, filling them in, setting up the wires, etc.

For refraction applications, the VIBSIST technique is at least 10 times faster than using a sledgehammer and for reflection more than 10 to 20 times faster than using explosives, depending on the operator.

With the VIBSIST-20, you can finish the job quite sooner than with alternate methods.

HIGHER DATA QUALITY

The VIBSIST-20 produces high frequency content (up to 2500 Hz) while achieving significant depth penetration as shown on Figure 1. The high frequency content of the signal emitted by a seismic source tends to decrease when the power of the source increases, which makes higher resolution and wide investigation range difficult to achieve simultaneously. The investigation range can however be increased with little or no expense of resolution if the signal energy is built over time, rather than being emitted as a short high-power burst. 

Figure 1: Axial component receiver gathers obtained at GTS Grimsel Tunnel site, Switzerland from a single pulse source (PH-62 on the left) and the VIBSIST-20 (on the right)

MODULAR AND PORTABLE

The reduced number of modules make the VIBSIST-20 portable and highly mobile. It allows jobs to be done faster and in difficult field conditions that would otherwise have been almost inaccessible such as mountainous regions, underground mines, confined areas, etc.

ADDITIONAL BENEFITS

ENVIRONMENTALLY FRIENDLY

The VIBSIST-20 is an environmentally friendly seismic source. It is a non-destructive alternative that does not create environmental pollution such as chemicals, sound, etc. Legal risks frequently associated with using explosives are eliminated.

MECHANICALLY RELIABLE

The VIBSIST-20 incorporates and upgrades standard rock breaker equipment commonly used in the construction industry. The many thousands of impacts per day used by the Swept Impact Technique require a rugged electromechanical hammer that is already well proven and that also meets established environmental (sound) standards.

COMPATIBLE WITH MANY SEISMOGRAPHS

The VIBSIST can be used with many seismographs. A correlator is required as well a large enough memory per channel. 

INTEGRATED WITH TUNNEL TO HOLE AND VSP SURVEYS

The VIBSIST-20 is ideal for tunnel to hole and VSP high resolution surveys. It generates enough energy to be used with borehole seismic systems at depth of 400 meters or less.

SURFACE WAVE CAPABILITY

The VIBSIST-20 can be used to produce and measure surface waves, which can be processed and analyzed.

SYSTEM COMPONENTS

The VIBSIST-20 includes the following modules:

1. The controller transfers to the impact hammer the sweep control sequence provided by the computer 

2. The impact hammer is modified to operate in accordance with the sweep control sequence. A power source such as a motor generator is needed to operate the hammer

3. The ground impact assembly includes an impact rod and a ground coupling plate (two versions are available depending on the ground conditions, either hard or soft).

4. A laptop is required but not provided with the VIBSIST-20.

The system also includes the necessary cables between the controller, the hammer and the seismograph.

SOFTWARE

Four software modules are included as part of the VIBSIST-20 system, they are:

• Controller, used to program the sweep control sequence

• Signal Decoder, deconvolves the long sweeps. It may also be used for On Line monitoring or Off Line processing.

• Signal Conditioning, includes a collection of filtering programs used for processing of the records before or after deconvolution

• Signal Display Interface allows the operator to visualize the data.

SPECIFICATIONS:

Power supply: 115 V / 60 Hz or 230 V / 50 Hz 

Maximum consumption: 13.6 A

Repetition rate: programmable between 15 to 32 impacts per second

Impact energy: approximately 20 J / impact for a typical hand-held demolition hammer

Impact frequency band: approximately 50 to 2500 Hz

Programmed sweep characteristics: computer controlled (any shape) or preset (linear) sweep .

Impact rate ratio: minimum 1.5 / 1.

Sweep time adjustment: 2.5 to 30 seconds (this is restricted by the number of samples available per channel).

Controller:

• Weight: 2 kg

• Dimensions: 300 x 120 x 60 mm

Impact Hammer:

• Length: 571.5 mm.

• Weight: 22.5 kg

Impact Rod

• Length: 300 mm

• Weight: 3.0 kg

Ground Coupling Plate

• Weight: 3.0 kg. (hard) 1.5 kg. (soft)