Police investigating the deadly collapse of the Canterbury Television building in the February 2011 earthquake will next week excavate the disaster site to examine the soil and foundations.

The South wall foundation and parts of the North wall foundation on the site where the six-storey Christchurch office block once stood are the latest focus for the complex technical criminal investigation which is yet to establish whether anyone will be charged with the building's pancake collapse, which claimed 115 lives.

On Monday, contractors will begin work to dig eight test pits or trenches to allow soil specialists and engineers to examine the soil and foundations.

"This site work is expected to be completed within the week and the site will then be reinstated to its former condition," Detective Superintendent Peter Read said.


The area will be fenced off and security will be in place limiting access to the site.

In September last year, police announced that they were working with engineering consultants Beca and making replicas of the structure to test its critical elements.

Read said that the process has now been completed.

"The results of this testing have been peer reviewed and factored into the ongoing investigation," he said, adding that the investigation is now nearing its closing stages.

Investigators have interviewed more than 100 witnesses and raided the offices of Engenium Consulting Engineers, formerly Alan Reay Consultants, which designed the ill-fated building in the mid-1980s.

"The outcome of the investigation, and any decisions on criminal culpability, will be communicated first to the families and then publicly," Read said.

"This is expected to occur later this year, however police are unable to give a more definitive time-frame at this stage."

The families of the CTV victims have been advised of today's update.

"We again thank them for their support and understanding while police has worked through this long, very complex and technical investigation," Read added.

In 2012, the royal commission of inquiry found serious errors by engineers, structural designers and the Christchurch City Council.

After the report's release, families and friends of the victims called for legal action to be taken against those responsible.

The commission said Dr Reay should have recognised that his employee David Harding was working beyond his limits when designing the building in 1986.