"biggest upheaval" is correct and usable in written English.
You can use it to refer to a drastic, often sudden, change in a situation or environment. For example: "The pandemic has caused the biggest upheaval many of us will ever experience in our lifetime."
Almost unnoticed, the biggest upheaval in Welsh government for 700 years took place on July 1st.
The UK is going through the biggest upheaval in the local news industry ever.
Now the industry is grappling with its biggest upheaval since the invention of high-speed printing presses and the railways.
But the biggest upheaval came with Rosie O'Donnell, who brought an aggressive tone, feuding with Donald Trump and sparring with Hasselbeck over the Iraq War.
In the biggest upheaval since the chart was launched in 1952, compilers have produced a ratio to "weight" a temporary stream against an actual song purchase.
He accused church leaders of promoting a belief that "this is somehow the biggest upheaval since the sacking of the monasteries" in the Middle Ages.
Under Grade and Thompson the corporation has undergone one of its biggest upheavals.
She was a revolutionary but also an incrementalist, whose biggest upheavals were mostly not announced in her manifestos.Mr Cameron is being similarly cautious.
The fare proposal comes amid a time of flux for the taxicab industry, which has recently experienced some of the biggest upheavals in its history.
As seen in Noshiro, some of the biggest upheavals followed the lifting of restrictions on large stores, a step originally urged by Washington to admit American retailers.
That may be distasteful to many outsiders but if pay structures better reflect information about the risks such star bankers are taking and if their pay levels do not inflate the compensation of everyone around them, it ought to be defended.The biggest upheavals in pay and in risk management will be in wholesale banking.
