Subsurface Cavity Survey Technology - Road Management Technology Center

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Road and Sidewalk Subsurface Cavity Detection Vehicles

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Subsurface cavity survey technology uses vehicles equipped with radar and other technologies to find cavities below the surface of the road rapidly and accurately.

Wide-ranging rapid surveys do not obstruct normal traffic.
The position of cavities is instantly specified with 3-direction video and GPS.
Three vehicles enable a national network to survey any location in Japan within eight hours.

Vehicles for subsurface cavity surveys on roads

Sidewalk survey vehicle

Cavities have been discovered at more than 4000 locations to date, preventing many sinkhole accidents.

Road surveys

Sidewalk surveys


Earthquake west of Fukuoka Prefecture (survey in 2005)		Niigata earthquake (2004) (survey in 2004)		Earthquake off Tokachi coast (Hokkaido) (survey in 2003)

Data analysis and cavity determination
The subsurface cavity detector vehicle is equipped with a multi-array antenna to identify the location and extent of a cavity.
The position of cavities is instantly specified with 3-direction video and GPS.

Subsurface cavity survey vehicle. Survey speed: 45km/h Survey width: 2.45m Survey depth: 1.5m Sidewalk survey vehicle Survey speed: 5km/h Survey width: 1.00 m Survey depth: 1.5m Cavity signal Three ITV cameras obtain position information.

Cavity Signal

ITV cameras

Douroscope		Void Scope
When a cavity is located, a 40-mm diameter core is bored, and a Douroscope used to record the an image of the cavity, including the depth and thickness.		The Void Scope is a device for imaging the interior of the cavity. It helps to determine the cause for the cavity.

Damaged drain

Damaged water supply pipe

Damage to attached pipe

Inadequate backfill
around manhole

Inadequate backfill
around utility pole

Inadequate backfill
where buried pipes
are close together

Inadequate backfill
around underground structure

Accumulated experience is used as a basis for efficient and accurate survey planning
Results obtained from surveys are analyzed from every angle, to understand the trends in the occurrence of cavities.
From projections of trends in the occurrence of cavities and the effects of subsidence incidents, high-priority areas for surveys, and the appropriate survey frequency can be assessed.

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