seems most project dont deal on real factors and just supposed on good way and condition but nature of humanity and society are most complex to predict correct on time ,these days most nation involve to low rate in economy growth so you can not count on good finanical source for the project,other relate to the nature and we do not know how handle this also.hope this help you through your question.

https://www.researchgate.net/publication/316701334_Preface_Energy_Investments_An_adaptive_approach_to_profiting_from_uncertainties

There are two aspects that I see in your question. One is the setting of an expected timeline and the deviations from plan. Two is implicit in your question which is what we can do about these deviations.

In my book, You may find the answers in the capital budgeting practices. I argue that because managers prefer a linear thinking on project execution, projects are valued where predictability of outcomes are rewarded while volatility is penalised. Following this reasoning, managers would aim to reduce volatilities by entering into rigid and inflexible contracting.  

Such rigid obligations are difficult to implement or comply given that markets and humans are inherently dynamic. As markets change, or needs vary, what was planned previously would no longer work. However, the rigid obligations would hold the contracting parties to what was agreed under different market conditions that are no longer workable. The only ways to correct this is to provide flexibility at the outset, or enter into repeated renegotiations. 

This brings us to the second aspect. Explicit evaluation of the value of operational flexibility using real options (usually applying binomial tree analysis) would highlight to the managers the value of flexibility under volatile markets.

Data Preface: Energy Investments: An adaptive approach to profiti...

Each engineering project has strength and weakness points, generally both of two items, resources and partnership are the weakness points and major reasons of delay.

Best wishes           

Article Performance Assessment of Three Companies (Road Construction...

There are multiple potential reasons and many have not been researched sufficiently.

For example, unprofessional project team-building in the early project stages (leading to unclear group norms and conflicting expectations), intercultural challenges including inconsistent and differing perceptions of the importance and nature of tools such as contracts, "leaders" who don't lead, etc.

I highly recommend you to study this thesis. A qualitative questionnaire was designed and distributed among construction practitioners to identify cost overrun and delay causes in different EPC phases of Civil Projects. It might be beneficial for you and your research :

https://www.researchgate.net/profile/Sharareh_Kermanshachi/publication/322477152/inline/jsViewer/5ba9737992851ca9ed23714a

https://www.researchgate.net/profile/Mohammadreza_Habibi/publication/325206822/inline/jsViewer/5b7acd45a6fdcc5f8b56b450

As project approval is not a single and simple way to grab it. Before submission of Project it need to be quantify timely and also need to submit in proper channel during this process it takes time to get aproval from concern organization. altimatly a project cost is always at increasing side.