Po Shan Drainage Tunnel – Landslide Sci-Tech Chamber

In 1972, the catastrophic landslide at Po Shan Road in the Mid-Levels shattered numerous homes and took away 67 lives. Post-disaster investigation revealed that the Po Shan hillside was affected by high groundwater levels and was susceptible to landslide. In the 1980s, the Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department (CEDD) installed horizontal drains in the Po Shan area to lower the groundwater table, thereby improving the stability of the hillside against large-scale slope failure. However, monitoring data in the early 2000s revealed that some of the horizontal drains exhibited a decreasing trend of water outflow and the groundwater levels could be rather high locally during periods of heavy rainfall. Subsequently, the GEO designed an innovative and sustainable groundwater regulation system to control the groundwater level in the Po Shan hillside, entitled the "Po Shan Drainage Tunnel". The system comprises a pair of drainage tunnels (3.5m diameter and a total length of 500m) and a network of 172 sub-vertical drains. It is equipped with an automatic real-time groundwater monitoring system to facilitate the GEO to control the groundwater levels; so as to reduce the risk of major landslides and enhance public safety.

Given the uniqueness of the Po Shan Drainage Tunnel and its novel features, the GEO established a "Landslide Sci-Tech Chamber" in the tunnel to convey the importance of slope safety to the public.