Most model based studies on project uncertainty investigate a single source of uncertainty, with a dominant focus on stochastic activity durations. However, another major uncertainty facing engineering projects is that of changes in design troughout the project delivery. This may come from uncertainty in the market, technology, or regulations, leading to changes in design and implementation paths, with alterations in the project network itself. This comes on top of stochastic and correlated activity durations for a given design. In this paper we develop a stochastic program to investigate how uncertainty in design and activity durations, together, affect planning, and their relationships. The findings suggest that when design uncertainty is modelled by multiple alternatives and delayed decisions on the final alternative, stochastic and correlated activity durations have limited impact. In situations with alternative and subtitutable solutions available for a given design, correlations drive a certain learning behaviour.

基于项目不确定性的大多数基于模型的研究都是研究不确定性的单一来源，主要关注随机活动的持续时间。但是，工程项目面临的另一个主要不确定性是整个项目交付期间设计的变化。这可能来自市场，技术或法规的不确定性，从而导致设计和实施路径的变化，以及项目网络本身的变化。这是给定设计的随机和相关活动持续时间的基础。在本文中，我们开发了一个随机程序，以研究设计和活动持续时间的不确定性如何共同影响计划及其关系。研究结果表明，当设计不确定性是由多个替代方案和对最终替代方案的延迟决策建模时，随机和相关活动持续时间的影响有限。在给定设计具有替代和可替代解决方案的情况下，相关性会驱动某种学习行为。