This document describes a new prototype system for conducting MASW2D (Multichannel Analysis of Surface Waves 2D) surveys for roadside investigations. The system allows for continuous seismic profiling along roads with minimal traffic interruptions. It features a mobile land streamer towed slowly between recording stations, an accelerated weight source producing high seismic energy, and onboard data recording. Examples show how MASW2D has been used to assess geology and soil properties for underground construction projects in Istanbul and Milan, and to investigate slope failures from abandoned quarries. The system allows MASW2D to be efficiently applied in noisy urban environments.

1. 87° Congresso della Società Geologica Italiana e
90° Congresso della Società Italiana di Mineralogia e Petrologia
10 - 12 Settembre 2014 - Milano
A new prototype system for MASW2D roadside survey
Mario Naldi, Emmanuele Duò – Techgea Srl (info@techgea.eu)

2. GROUND INVESTIGATION IN URBAN AREAS: A NEW FIELD FOR THE
NEAR SURFACE GEOPHYSICS
Urban areas represent some of the most challenging environments
for civil works:
•Metro lines
•Underground utilities (sewage, pipe lines, heating system)
•Underground parking
In such a context, the geophysical surveys can play an important
role for the assessment of the geology and soil mechanics
properties

3. Some “obstacles” should be considered in the
survey design :
1.Restricted space,
2.the necessity for traffic management,
3.high ambient noise (electrical and vibration),
4.underground utilities,
… all THESE issues help to complicate the design
and setting out of the geophysical profiles or
grids.
HOW TO SELECT THE RIGHT
METHODOLOGY

4. The conventional seismic
surveys (refraction or
reflection) can have many
limitations in urban areas:
•do not work well in noisy
areas
•take long time for data
acquisition (hard traffic
management)
•require high energy source
Among geophysical methods,
the seismic survey is the most
commonly applied
for civil engineering projects.
MASW 2D profiling has many advantages for surveys in urban areas:
•More energetic wavelets (less energy required)
•Short acquisition time with just one shot and fast move of the
geophone layout (no stop of the road traffic)
•Favorable ratio between the length of the seismic line and the soil
depth. MASW2D = 1:1  seismic refraction = 5:1
Seismic surveys in urban
areas

5. Among geophysical methods,
the seismic survey is the most
commonly applied
for civil engineering projects.
Seismic sources generate a continuous spectrum of surface wave frequencies.
Where there is vertical velocity variation, different frequency waves travel at different
phase velocities. This is dispersion. By examining dispersion curves (phase velocity vs.
frequency), we can determine material properties (e.g., layer thickness, depth, Vs) via Inversion
BASIC THEORY OF MASW
Lower frequency
 deeper strata
DISPERSION
INVERSION

6. Low density shallow soil
Gravel and sand (not cemented)
Gravel and sand (partially cemented)
Masw2D (Vs - m/s)
Seismic refraction (Vp – m/s)
Low density shallow soil
MASW2D HAS A HIGHER VERTICAL AND LATERAL RESOLUTION COMPARED WITH THE
REFRACTION METHOD
Velocity inversion in the subsurface is one of the most serious limitations of the
shallow seismic refraction method  GEOPHYSICAL IMAGING HAS A POOR
HIDDEN
HIDDEN

7. How to improve MASW 2D survey efficiency in urban areas?
1.Mobile system  continuous profiling (no traffic interruption)
2.High seismic energy  bypass of the urban noise
Slow motion
(low gear)
STOP: One shot and recording (20 seconds)
GO: Slow move to the next station (2 m)
String of geophones on
a land streamer
Source of energy
(ACCELERATED WEIGHT)
Seismograph on board
(DATA RECORDING)
The streamer is towed at low speed with
stop at every recording station

8. Winch
(powered by a 100 Ah/12 V
Battery)
Traction springs
Propelled mass
Uncoupling devices
Source of energy
(ACCELERATED
WEIGHT)
Lift
The prototype has
been designed and
produced for
Techgea by TREFFE

9. Land streamer
Sensors (4.5 hz geophones)
mounted on a metal plate)
String of geophones on a land
streamer
Source of energy
(ACCELERATED WEIGHT)Seismograph on board
(DATA RECORDING)
The streamer is towed at low speed with stop at every recording
station

10. Distance [m]
Küçükbakkalköy station
projection
COLOUR SCALE
Shear wave velocity [m/s]
Made ground and/or soft soil
[Vs: 0÷200 m/s]
Dense soil and/or overburden
[Vs: 200 – 370 m/s]
Very dense soil/soft
rock
[Vs: 370÷800 m/s]
Rock
[Vs: 800÷1200 m/s]
Hard rock
[Vs > 1200 m/s]
800
m/s
370
m/s
200
m/s
1200
m/s
Remark:
soil classification from ASCE table (7-2005),
(modified)
Fault zone
Solid rock (LIMESTONE)
Fractured rock
Fractured rock
Weathered rock
Top soil
Line M5-13 - Shear Wave section
Weathered rock
Küçükbakkalköy station
EXAMPLE 1 – ISTANBUL METRO LINE BOSTANCI – DUDULLU (TURKEY)
Masw2d SURVEY FOR THE GEOLOGICAL ASSESSMENT AND THE
SEISMIC SOIL CLASSIFICATION
Fault zone
THE MASW2D LINE IS POSITIONED ALONG A ROAD BETWEEN THE PROJECTION OF THE TWIN TUNNELS
OVERNIGHT SURVEY

11. EXAMPLE 2 – SEWER PIPE SETTLEMENT (MILAN AREA, ITALY)
ROAD SUBSIDENCE AFTER THE PIPELINE POSITIONING
CEMENTED ZONE (GROUTING BELOW THE
DEFORMED ROAD)
DENSE GRAVEL
VERY LOW DENSITY SAND-
GRAVEL/VOIDS
SUBSIDENCE AREA
SUBSIDENCE AREA
SUBSIDENCE AREA

12. EXAMPLE 3 – SLOPE FAILURES ASSOCIATED WITH ABANDONED
UNDERGROUND QUARRIES (Alessandria, Italy)
ROAD SUBSIDENCE AND DEFORMATION
BA
Siltstone (soft rock)
Highly weathered siltstone
(silt consistency)
Landslide projection (IFFI)
S1
Very low density zone
(collapsed tunnels)
Tunnel
Subsidence area
Subsidence area

13. 87° Congresso della Società Geologica Italiana e
90° Congresso della Società Italiana di Mineralogia e Petrologia
10 - 12 Settembre 2014 - Milano
A new prototype system for MASW2D roadside survey
Mario Naldi, Emmanuele Duò – Techgea Srl
Thank you for the attention