The new Genting Sempah tunnel represents an important part of the widening and upgrading of the main east-west road link between Kuala Lumpur on the west coast and Kuantan on the east coast of Peninsular Malaysia. The new tunnel is located between 18m to 30m north of the existing (old) tunnel which was constructed in 1975 and has a similar alignment. Engineering geological investigations and site characterization for the construction of the new tunnel were carried out in 1994 with drilling, aerial photograph interpretation, surface geological mapping, geophysical surveys and laboratory testing. Rock mass classification was carried out based on the Q classification system of Barton et at. (1974). Based on this classification, it was predicted that for the tunnel zone, 8.6 % of the length of the tunnel consisted of rock mass classified as very poor i.e. type two, 82.8% as extremely poor, i.e. type three and the remaining 8.6% as exceptionally poor, i.e. type four. Excavation of the tunnel between March 1995 and September 1996 together with engineering geological logging and rock mass classification revealed the following; type two, very poor 6.3%, type three, extremely poor 89.9%, type four, exceptionally poor 3.8%. These results show the general validity of the prediction of the rock mass quality.
Terowong kedua Genting Sempah merupakan suatu bahagian utama dalam pembesaran dan peningkatan taraf jalan timur-barat utama yang menghubungi Kuala Lumpur di pantai barat dan Kuantan di pantai timur Semenanjung Malaysia. Terowong kedua berkedudukan 18 m hingga 30 m ke utara terowong lama yang dibina pada tahun 1975 dan mempunyai penjajaran yang sama. Penyiasatan geologi kejuruteraan dan pemeriksaan tapak pembinaan terowong kedua dilaksanakan pada tahun 1994 dengan penggerudian, pentafsiran fotograf udara, pemetaan geologi permukaan, survei geofizik dan ujian makmal. Pengelasan kualiti jasad batuan dilakukan berdasarkan sistem pengelasan Q oleh Barton et al. (1974). Hasil pengelasan ini di zon terowong meramalkan 8.6% panjang terowong baru terdiri daripada jasad batuan berkualiti sangat rendah, iaitu jenis dua, 82.8% berkualiti tersangat rendah, iaitu jenis tiga manakala 8.6% panjang terowong terdiri daripada jasad batuan berkualiti luarbiasa rendah, iaitu jenis empat. Penggalian terowong di antara Mac 1995 dan September 1996 dengan rakaman geologi kejuruteraan dan pengelasan jasad batuan semasa penggalian menghasilkan keputusan seperti berikut; jenis dua, berkualiti sangat rendah 6.3%, jenis tiga, berkualiti tersangat rendah 89.9%, jenis empat, berkualiti luar biasa rendah 3.8%. Keputusan