V i a P a s t r e n g o 9 , 2 4 0 6 8 S e r i a t e ( B G ) T e l . + 3 9 0 3 5 4 5 2 0 0 7 5 W e b s i t e : w w w . s o l g e o . i t E - m a i l : i n f o @ s o l g e o . i t

P r o c e d u r e _ C H + t o m o _ E n g _ v 8 . d o c x

SEISMIC CROSS-HOLE SURVEY

SOLGEO SPECIALIZES IN GEOPHYSICAL SERVICES APPLIED TO ENGINEERING AND GEOTECHNICAL PROJECTS.

SOLGEO ALSO DEVELOPS, PRODUCES AND SELLS DEVICES USED FOR SEISMIC OR ACCELEROMETRIC DYNAMIC MONITORING, OR FOR

NONDESTRUCTIVE TESTING ON STRUCTURES.

SOLGEO’S MULTIDISCIPLINARY EXPERTISE ALLOWED THE COMPANY TO DEVELOP EXTREMELY ADVANCED MONITORING

SYSTEMS, ESPECIALLY IN THE DYNAMIC SIGNAL ACQUISITION FIELD.

SOLGEO, THANKS TO THIS KNOW-HOW, IS NOW PARTNER WITH SOME WORLD RENOWNED COMPANIES..

2 SOLGEO | Seismic Cross-Hole Survey

The new cross hole set provided by Solgeo

SOLGEO | 3

- INTRODUCTION –

Geophysical survey called “Cross-Hole” consists in the determination of horizontally travelling compression (P) and shear (S) seismic waves on t site, using two or three boreholes. (ASTM D4428/D4428M-07).

SOLGEO produces its own equipment allowing to perform measurements quickly and very reliable.

In order to obtain compressional (P) waves and share (S) waves velocity soil profile, two steps of measurements are performed:

For P waves analysis an energy source SPARKER™ together with hydrophone receivers

For S saves analysis an electrodynamic waves generator, GEOS-H™ and geophone receivers, that are clamped to the hole housing with a pneumatic system.

The new P&S receiver configuration developed by Solgeo to perform cross-hole tests in a fast way: a unique cable for hydrophone and

vertical geophone

4 SOLGEO |

- COMPRESSIONAL P WAVES -

To generate P waves an automatic energy source, SOLGEO SPARKER™ is used; it can work at many different levels of power (from 100J to 1000J, normally 300J) and it must be used in boreholes filled with water, up to 200 m depth.

Figure 1: Electrodynamics power supply EG&G (from 100 to 1000 J), for P and S waves generation (sx) and new SOLGEO Acquisition Unit

An hydrophone is used as receiver of P waves in a borehole filled with water.

Figure 2, 3: P waves transmitter, SPARKER™ (sx) and its frequency signature (middle) obtained in a sand-lime sequence. (Dx) The new SOLGEO Hydrophone

Acquisition Unit

SOLGEO | 5

- SHEAR S WAVES -

The energy source SOLGEO GEOS-H™ generates automatically polarized waves, working up to 200 m depth (also water filled).

The energy source is made by two parts: a central section, for pneumatic clamping and upper and downer parts that contain electrodynamic waves generator. The device allows to generate alternatively upwards and downwards signals, in order to obtain shear waves polarization.

Shear waves first arrival can be detected in a reliable and precise way, compared with other system.

Figure 4, 5: Electrodynamics transmitter for S waves GEOS-H™ (sx) Geophone receiver ATG-14 (dx) and its relating pneumatic clamping system

A vertical geophone receiver, SOLGEO AVG-14™ (Amplified Vertical Geophone), containing a 14 Hz vertical geophones, with a preamplified electronics and gain control.

Clamping at borehole housing is provided by pneumatic system(working depth up to 200m of depth).

6 SOLGEO |

- ACQUISITION UNIT & SOFTWARE -

Data are recorded with a digital acquisition system by SOLGEO with high sample rate (up to 2MHz) and dynamic (more than 110 dB), with specific software WinCrossHole™.

The system allows to perform averaging of signal (stack) in order to obtain improvement of signal/noise ratio, thanks to electronic triggering system embodied.

Figure 6, 7: Acquisition unit MiniRec™ and its power supply Battey Box™, designed and produced by Solgeo.

P&S waves transmitter sources have a triggering system electronically controlled, this means that the trigger signal is perfectly constant and delays are always measurable

For this reason, the equipment used allows to perform measurements using only two boreholes, avoiding costs of third borehole, in full compliance with ASTM standards.

Figure 8, 9: WinCrossHole™ software, by Solgeo, permits to acquire and pick P wave (sx) and S wave first arrival (dx) acquired during acquisition.

SOLGEO | 7

- INCLINOMETER SURVEY -

In order to obtain the S and P waves soil velocity it is necessary measuring real distance between boreholes at any measurement depth. The deviation logs that measures direction and inclination of the holes in 3D space, are obtained by INCLIS-DH probe™, designed and constructed by SOLGEO.

It allows to perform three-dimensional survey of the verticality of boreholes, carrying out simultaneously inclination and azimuth.

Figure 10, 11: Inclinometer Probe INCLIS-DH (Above) and its Acquisition Box (dx)

The probe contains a triaxial magnetometer (giving the angle of azimuth relative to the measured earth magnetic field) and a set of three accelerometers, used to measure tilt and spin relatively to the measured force of gravity,.

For each borehole two series of measurements are performed: one on the way down and one in the way up, at constant intervals of 2 meters. Values obtained are then interpolated at 1.0 m steps and used to calculate the distance between generation and receiving points in the boreholes.

PROBE CHARACTERISTICS

DIAMETER 40 mm LENGTH 100 mm WEIGHT 4 kg

RANGE OF MEASUREMENTS

AZIMUTH +/- 0.5° INCLINATION +/- 0.2°

ORIENTATION RANGE 360° OPERATING TEMPERATURE 0-125°C MAXIMUM WORK PRESSURE 20 bar

8 SOLGEO |

- SONIC LOG SURVEY -

To check the quality of contact between the boreholes casing and the soil, (i.e. to check the goodness of the cementation) a continuous sonic log into each borehole should be performed.

Signals are reproduced as sonic variable density diagrams (with conventional name of “diagraphy”), which represent the sequence of the sonic signals as a function of time (horizontal axis) and depth (vertical axis).

When the grouting quality between soil and casing is constant, the diagraphies show uniform characteristics; presence of voids or bad contact is readily shown by variations of the recorded signal characteristics.

Figure 12: Sonic logging results (sonic diagraphies); on the left chart in blue line, velocity profile along borehole. In yellow: grouting failure. Sonic probe made by a transmitter and a receiver

separated by 1m acoustic isolating material (dx).

DEFECT

DEFECT

DEFECT

TRASMITTER

RECEIVER

SOLGEO | - S and P seismograms - 9

- S AND P SEISMOGRAMS -

Figure 13: Cross Hole intermediate results. Waterfall plot of recorded seismic traces: signals on the left and P signals on the right.

10 SOLGEO | - S and P calculated velocity profiles -

- S AND P CALCULATED VELOCITY PROFILES -

Figure 14: Finale Cross Hole results: velocity profile for S waves (sx) and P waves (dx). For each velocity its Poisson’s ratio and Elastic Module value is associated.

SOLGEO | - Cross-Hole tomography results - 11

- CROSS-HOLE TOMOGRAPHY RESULTS -

P waves Tomography merging 5 boreholes (Italy)

Figure 15: P waves tomography obtained through merging of 5 boreholes In the picture a normal fault is

well shown in the left part

FAULT

GYPSUM FORMATION

SILT STONE AND SANDSTONE

SILT STONE AND SANDSTONE

12 SOLGEO | - Cross-Hole tomography results -

P waves Tomography through 3 boreholes not lined (Italy)

Figure 16: Above, P waves tomography through boreholes couples Bottom, pposition of 3 boreholes and 3D tomography view

SOLGEO | - Cross-Hole tomography results - 13

P and S waves Tomography (Abudhabi)

Figure 17: P waves tomography in a boreholes couple. On the left, stratigraphy information and on the

right the calculated ray paths needed for tomographic inversion

14 SOLGEO | - Cross-Hole tomography results -

Figure 18: S waves tomography in a boreholes couple. On the left, stratigraphy information and on the

right the calculated ray paths needed for tomographic inversion