Reasons for high cost of project variations

IN light of many massive variations in construction projects, I wish to pinpoint how we can minimize it.
Firstly, variations are inevitable in any projects but must be within a manageable level in terms of cost and time.
In any contract, variations or uncertainties are prepared for in advance by the design engineer to be taken care of under contingency, normally 10% of the accepted contract price.
So why do variations sometimes go up from 20% to 70%?
The main reason out of others is because of poor project definition and design which takes place in the early stages of the construction process. The contract price is as good as the design itself.
Let me give a typical scenario of what happens in the project definition and design process before and during construction.
The client without knowing what kind of building to be constructed goes ahead and engages a design engineer or consultant to build a hotel. So the consultant, having designed many hotels before, does not bother to go to the site to get detailed information.
Instead he goes ahead and produced design in Australia when the hotel is to be built in Papua New Guinea, editing past calculations and drawings from similar hotel designs.
The design engineer then hands over the designs with drawings to the client who submits the documents for tender without probably reviewing it.
When the contractor who has won the bid goes to site to start the construction, he realises that many things or conditions on site are different to those specified in the technical specifications.
He also finds out that some of the structural materials are not in PNG and are very expensive to ship from overseas so he starts requesting for variations.
To inflate the variation even further, the client realizes that he doesn’t like the shape or type or kind of materials being used for the structure thus suggesting variations.
For instance, if the client is the Government, he starts getting more taxpayers money to achieve his desired outcome.
How can we minimize it?
To minimize the variations, the design team must be made responsible for any variations exceeding 10% of the contract price due to their failures or incompetency.
The client must conceive the project in his mind and define thoroughly to the design engineer and other professionals.
Moreover, the contractor must go to the site and do investigations, understand the drawings and specifications thoroughly prior to biding for the project.

Apulin Yaka Buie, Via email