Projects & case studies
- Sinkhole detection
- UXO detection
- Finding construction piles
- Concrete wall location
- Metal cylinder detection
Right: transillumination data, boreholes A-B
- Larger detection range from the borehole which means fewer boreholes are required.
- TISA 2D enables to search underneath obstacles at the surface, such as buildings or metallic structures which would disturb the magnetometer readings.
In an UXO detection project in the capital city of Germany reflection data from TISA 2D was acquired to help with the investigation of possible UXO locations.
Several boreholes were drilled around different target locations spread over the whole city. TISA 2D reflection measurements were conducted to a maximum depth of around 7 meters below the surface. The soil conditions were described as ranging from dry sands to loamy sand in one target location.
In the data set below a strong reflection is visible in a depth range of 2.5 to 3.5 m below the surface. The radial distance of the reflection from the borehole is around 2.3 meters. Excavation of the object showed the presence of a 250 Kg aerial bomb. TISA 2D is a valuable addition to the typically used suite of detecting tools for UXO.
T&A Survey investigated for a client as to whether a target site for a future shipyard (inset figure) was loaded with old construction piles or with UXO’s. This was done to prevent large excavation costs for false readings of possible UXO’s. Given the anticipated depth, dimensions and material of the two types of objects, TISA 2D was chosen to tell the objects apart.
Surface magnetometry was used first to define the regions of interest and to define the target locations for TISA 2D. Several boreholes around each target locations were drilled and TISA 2D deployed to distinguish the two types of objects. The soil conditions on the survey site were described as intervals of dry sand and clay.
An example of an imaged pile can be seen in the figure below. The elongated reflection in a depth range of 6-11 meters below the surface indicates the presence of a pile, rather than a point shaped UXO. With the results of this survey TISA 2D could explain the nature of the magnetic disturbances and prevent the need for an expensive UXO excavation. TISA 2D is the right tool for these kinds of jobs, as it is highly sensitive to planar reflectors like piles and pillars.
< The elongated reflection with a length of several meters indicates the presence of a pile instead of an UXO.
To assess the locations of the tunnel network, two boreholes were drilled to a maximum depth of 11 meter below the surface. One of the two boreholes, shown in the above photo, was located approximately 3 meters from the expected lateral position of the tunnel network. From both boreholes TISA 2D reflection data were acquired and subsequently interpreted for the location of burried tunnel structures.
One of the two data sets shows a relatively strong reflection in a depth interval of 9-10 m below the surface. With a calculated soil velocity of 0.13 m/ns the lateral distance from the borehole was found to be around 3 meters. This reflection, as marked in the figure below, was interpreted as the top section of the adjacent tunnel network.
- A metal cylinder with a diameter of 130 mm and a length of 1 meter was placed inside a borehole. The test object was suspended at a depth of 5 meters below the surface. TISA 2D was deployed in a second borehole at a horizontal distance of 1.8 meters from the first borehole. This borehole allowed measurements down to a depth of 7 meters below the surface.
A bigger metal cylinder with a diameter of 200 mm and a length of 0.8 meters was placed inside a borehole. The test object was again suspended at a depth of 5 meters below the surface. TISA 2D was deployed in a second borehole at a horizontal distance of 2.9 meters from the first borehole. This borehole allowed measurements down to a depth of 8.4 meters below the surface.
Figure 1 shows the recorded data in the above described configuration 1. The vertical axis of this figure shows the depth below surface level, starting at 0 meter in the upper left corner. The horizontal axis shows the arrival time of the reflected signal given in nanoseconds. The dataset shown in Figure 1 is corrected for the reflections of the nearby borehole. At an arrival time of 50 ns strong reflections are visible in a depth range of 4.5 to 5.5 meters. The hyperbolic reflection patterns are typical for an object with limited vertical extension, like the used test cylinder.
Figure 2 shows the data for measurement configuration 2, where the metal cylinder is placed in a horizontal distance of 2.9 meters from the measuring borehole. The presented data is processed in the same way as Figure 1 and shows a reflection hyperbola starting at an arrival time of 75 ns. Despite the 60 % larger distance between TISA 2D and the metal cylinder, the data clearly shows the reflection signature of the test object in around 5 meters depth.
|Figure 1||Figure 2|