As a starting point, you may wish to get your hands on the the original documents, plans, plans, budgets, etc that justified the need for that intervention in the first place. Having a thorough understanding of the background information would enable you to then develop your methodology to evaluate the intervention and  move on from there.

All the best.

This is an interesting one, however you may well find the intervention is too far in the past to get much information about it. If it collapsed 10 year ago, the original planning documents could be up to 20 years old and forgotten on office shelves or archived who knows where.

A start would be to identify the various interest groups involved and try and get their documentation, If it was an aid activity there will be the donor agency, the government counterpart, the implementing agency and the recipient group/s. Their historical documentation should give you the plans and progress reports (of which there would have been many if it was a large aid intervention), and, maybe, the reasons for its collapse. The documents should allow you to identify key players from all groups to trace and interview. You may also be able to identify project indicators that it might be possible to reassess for any long term impacts, planned or unplanned. Keep in mind that because the intervention failed these groups will probably blame each other if they are willing to expose a failure at all!