It is an expectation that the PhD would make an original contribution and/or advance knowledge in a given field. I understand this is a universal assumption for this level of study across all universities.
One of my friend's research experiment has not produced a single positive result. This was a science experiment, so it is easy to quantify whether the result is positive or negative.
[It is a bit different in the social sciences, where the outcome (result) would be that either the null hypothesis is supported or rejected (with some analysis on the effect size to make the analysis meaningful in a given context). In other words, the data analysis either supports or does not support the proposition that is being investigated.]
My question is: What should a student do if none of the research outcomes or results are positive?
Simply writing that nothing new was found does not add or advance knowledge other than to just confirm the status quo (which I guess is a form of contribution, but there has to be more than this at this level of research!).