�We want to make sure that works have been carried out correctly at all projects where similar technologies were used,� says Herbert Bodner, Chairman of Bilfinger Berger A.G., Mannheim.

Suspicions by the investigators of the Cologne collapse prompted the new probe of work on the high-speed line.

In parallel, diaphragm walls being used in construction of one the North-South line’s new underground stations have been found to be about 80% short of specified dowel bars.

These as yet unconnected findings in Cologne recently emerged from investigations into the March 3, 2009 collapse. The archive building was undermined when a section of railroad tunnel under construction in nearby Waidmarkt collapsed. No official cause for the tunnel failure has yet been revealed.

The quality of construction  records  was “absolutely unacceptable,” says Bodner in a recent letter to Cologne’s mayor, Jürgen Roters. Bodner adds: “Despite the inaccurate protocols, no geometric deviations have occurred in the diaphragm walls that would endanger their stability”.

Bilfinger Berger is in the Cologne project’s construction joint venture with Wayss & Freytag Ingenieurbau A.G., Frankfurt, and Ed. Züblin A.G., Stuttgart.

The joint venture has completed around 80% of its contract with the city’s transportation authority Kölner Verkehrs-Betriebe AG (KVB) to build 3.3 km of twin tunnel and seven stations, says a spokesman.

A number of joint venture workers are being investigated over the faulty records, says the spokesman. Police carried out house searches late last month. Suspicions were raised when survey data of diaphragm wall excavations were found to be identical for different locations.

Bodner, in his letter to the mayor, also decries the omission of dowel bars between diaphragm wall panels. "For me, as an engineer, the failure to install shear dowels...is inconceivable and something that I have never seen in all my years of professional experience" he writes.

Missing steel bars was first spotted at the Waidmarkt collapse pit late last month, according to KVD. Exploratory cut-outs of diaphragm walling at Heumarket station, started on 10 February, found only 17% of the required steel bars in places, add KVB officials.

The station box has been declared structurally adequate. But the joint venture is planning “precautionary measures” in case the ground water should rise, increasing wall pressures.

According to Bilfinger Berger,  the contractor used similar technology on its project to build 35 km of high-speed railroad between Nuremberg and Ingolstadt. The $690 million contract included construction of over 40 bridges and 3.6 km of tunnel.

While Cologne’s prosecutor continues investigations, construction along the North-South line is going on except at the Waidmarkt collapse site. There, the city workers and volunteers are painstakingly recovering thousand of valuable records from the archive ruins.

Over 80% of the records have been recovered but over a third have been severely damaged, according to city officials. They estimate the cost of restoring the archive at up $550 million.