Shotcreting ruins soil, adds to heat island effect, expert says

Academics and conservationists have given the thumbs down to the use of shotcrete for slope works because of its cost, the damage it wreaks on the environment and other side effects.

Jim Chi-yung, University of Hong Kong's chair professor of geography, said that despite the government's claim to the contrary, shotcreting was used in most slope stabilisation works.

'[Such a method] is extremely destructive to soil, vegetation and hydrology because all existing ground cover and undergrowth are removed; soil is compacted and sprayed over with shotcrete. The soil that remains is not suitable to grow trees in,' he said.

Professor Jim said extensive use of shotcrete aggravated the urban 'heat island' effect because the material absorbed heat during the day and release it at night. 'It also blocks rain water from penetrating the soil, and as a result the rain drains down hills and floods the [lowlands].'

Conservancy Association conservation manager Ken So Kwok-yin said that in some private slope maintenance works property owners employed the cheapest method, where shotcrete was sprayed indiscriminately on slopes, covering tree roots and trunks. 'This material is strongly alkaline and the trees die within three or four months,' he said.

Mr So said using soil nails - which involved planting concrete beams onto soil - could be a more viable alternative as it secured the soil surface and allowed for retention of turf.