site characterisation study - phases 1 and 2 - HKU Libraries - The ...

- 6 -In Phase 2 the Group 1 and 2 techniques were further tested at four new sites againconsisting of, two pre-war masonry walls, one cut slope and one fill slope. The Phase 2 sites hadno existing ground investigation data so as to allow the Working Group to assess if thegeophysical methods alone can be reliable and accurate without any pre-conceptions of the siteconditions. Preliminary interpretations were made by each of the contractors based solely on thegeophysical results. Subsequent conventional ground investigations by GEO were then carriedout at the sites and the results were given to each of the contractors for re-interpretation of theirgeophysical results.The Phase 2 trials concluded that the overall quality of the raw data and interpretationsvaried significantly with the expertise of the individual geophysics teams. Certain contractorswere able to demonstrate that a combined geophysical investigation utilising GPR and RI canlocate the back of masonry walls if they are less than 3m thick and define zones of elevatedmoisture content and voids with reasonable accuracy. Only limited success was achieved indetermining the location of corestones and the thickness of loose fill at the two slope sites.In the light of the conclusions from the field trials, it is recommended that due to theinconsistent raw data and interpretations it would not be advisable at present to let a termcontract specifically for non-invasive geophysical techniques for site characterisation in HongKong, or to require the use of such techniques in LPM studies. Also, further trials of the four orother techniques are not warranted. However, since some of the results were encouraging it isrecommended that further research work on developing GPR and RI for masonry wallinvestigations is carried out through a local University with support from GEO. The researchshould focus on ways to enhance the resolution of the two techniques and also to develop a siteand data processing methodology which would ensure more consistent results from contractors.