A project manager discovers that a project problem has occurred.

Thank you for invitation >>>

with answer of Ayoub Tartir and i will add this: if some risks don't happen and will not happen at futur in the risk registers, the solution to take their costs to this new risk which not in risk logs>> 

Need to hold an immediate meeting with the project sponsor/senior management to discuss this issue and look for a best risk-based and cost effectiveness solution. In other words, the project should not be closed down, except if the sponsor approved to close it.

I agree with Mr. Bosman and Mr. Al Yazouri. To those answers I would add that the contract needs to be reviewed as well. Provisions likely were addressed (or at least should have been) in the contract itself as to the procedure in the event of force majeure or unforeseen circumstances.  Proper Planning Prevents Poor Performance!  Realize that you need to plan ahead at the contract phase for unexpected problems.  They can and do occur.

Call for a meeting between concern parties, explain, open a claim with project control manager and investigate to find out whose responsibility is it, and go from there.

We need to assess  the occurred problem to look for the quantified impact on project constraints. So we know what Extras are needed!

As said, The risk was not really identified. So the risk is Unknown and funds can be requested from Management Reserves after Board approval. 

However, If the risk occurred by misplanning or lack in knowledge of PM, I recommend the below response.

If the risk management process were ideal and driven perfectly. I assume some risks were closed in previous stages that can accommodate the cost of the new occurred risk. 

This an “unknown-unknown” risk type so you have to use a management reserve to manage its impact after management approval.

for more details please have a look on the following article,

http://pmstudycircle.com/2012/02/contingency-reserve-vs-management-reserve/

Hope this can help

The project Manager will go to the organizational process asset library and finds a Work Break Down Structure.

Thank you my brother about your invitation ,,, It is known that the implementation of civil engineering construction contracts being drafted based on the general conditions for the implementation of contracting civil engineering and I do not know how different paragraphs of those terms between one country to another, and in all cases must Resident Engineer to act on the basis of the powers conferred upon him under those established on the basis of the contract formula, and for me I will answer based on the conditions of public two sections I and II in my,,, Article52 and Article53 of the General Terms cover the case of the question, where has the right to make changes and calculating the value of changes in certain limits up to20% conditions the increase and decrease of the quantities contained in the table quantities calorimeter based as stated in the articles above.

Thank you for invitation Dear brother. Actually in most of the project unforeseen cost are taken into consideration with some percentage to the project cost and that is considered during time of approval of the project. But if that is not included during time of approval then meeting should be arranged with all stake holders for the solution of the problem.

The first step would be to call the project members together immediately to assess the risk in depth. this will be to quantify the oversight but more importantly to establish what other risks might come in to play. Remedial actions need to be formulated as soon as possible and after this the risk must be re-evaluated. Only after this would I would I approach my management. The worst thing that I believe is that people tend to overreact rather first doing due diligence to problems before reporting such. Go to your manager with the problem but make sure that you have suggested remedial actions, otherwise it will be viewed that you passing 'the preverbual monkey'. To continuously revisiting the risks and to rank them with probabilities and additional remedial actions with your team is a must! Risks are a fact of life but remedial actions taken is what differentiates a good project manager.