Investigation work at the site of the landslide close to the entrance of the Harbury tunnel near Leamington Spa is believed to have been caused by an unexpected vertical fault.
Network Rail route delivery director Karl Budge revealed the preliminary findings of the analysis during a visit to the site by transport secretary Patrick McLoughlin yesterday.
According to Budge, the cutting at Harbury has suffered from persistent stability issues for the last 20 to 30 years. Contractor J Murphy had been on site for four months working on a scheme designed to resolve the problem when major ground movement started on 31 January.
“We had completed 75% of the work, when we started to find small cracks opening up in the slope above the cutting,” said Budge.
Investigations of the incident showed that there was a previously unrecorded vertical fault at the back of the cutting. “All the information we have on geology around this cutting, and all the geological maps of the area, had not shown this before,” said Budge. “All the faults recorded previously have been horizontal.”
The landslide has resulted in the movement of 350,000t of material. Murphy has already moved 30,000t from the failed slope.
During his visit, McLoughlin said: “I regret rail passengers are still being inconvenienced by this serious landslip, but Network Rail’s main priority is to re-open the line as quickly as possible and when it is safe to do so.
“I have seen how hard Network Rail engineers are working to resolve this situation, and train operators have told me they are doing everything possible to give passengers up-to-date information and to keep them moving. My officials are closely monitoring the situation and will offer whatever support is required.”
Network Rail cancelled its planned closures of the West Coast main line in February for improvement works to ensure passengers can continue to travel between Birmingham and London while the landslip is resolved.