Remote tree root mapping using a tree trunk vibration method

Abstract

Tree roots are well known to be disruptive to underground pipe and cable networks, in particular water pipes and sewers. Damage can occur due to a number of different mechanisms: via direct penetration of the pipework resulting in leakage; through alterations in the ground water content locally, thus potentially destabilising the ground; or by means of a gradual displacing of the pipework from its original location, this possibly resulting in pipe fracture. Detecting the extent of root development of individual trees from the ground surface could therefore potentially identify areas of infrastructure which are particularly at risk from this kind of assault. ‘Mapping the Underworld’ (MTU) is an on-going research initiative that is seeking to address the consequences arising from an inability to consistently locate the buried utility service infrastructure without resorting to extensive excavations. To date, MTU has primarily focused on developing a prototype multi-sensor platform that can be used to improve the probability of detecting all buried utilities below the ground surface The technologies under investigation have included ground penetrating radar, lowfrequency quasi-static electromagnetic fields, passive magnetic fields and low-frequency vibro-acoustics. MTU has recently entered a new phase, ‘Assessing the Underworld’, in which the technologies developed thus far will be progressed to allow not only location of the buried infrastructure but remote assessment of its condition. It is within this framework that the tree vibration research described here is being undertaken. A vibrational pipe location method, which involves excitation of the pipe at some known position along with concurrent vibrational mapping of the ground surface, has been presented previously. It has been found that a simple correspondence exists between the wave propagating in the pipe and that measured on the ground surface. By examining the unwrapped phase of the vertical component of velocity measured on the ground surface, the run of the pipe can be found. This method has been modified to ascertain if the location of a tree’s roots can be similarly determined. The aim here is excite the trunk of a tree above the ground surface and then map the course of its major roots buried underground from measurements of vibration made at the ground surface. This paper presents the results of preliminary investigations

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