"gradual collapse" is correct and usable in written English.
You can use it to describe a situation in which something gradually deteriorates or fails over time. For example, "The gradual collapse of the industry meant that many workers lost their jobs."
Many locals are alarmed by the gradual collapse of amenities in Sarcelles.
The gradual collapse of Isis in Iraq and Syria, Irish security experts suggest, may result in fighters returning home.
Clare documents both the destruction of place and people and the gradual collapse of his own state of mind.
In September, the Peruvian media broadcast a videotape apparently showing Mr. Montesinos bribing a Peruvian congressman, starting a gradual collapse of the Fujimori government.
Gradual collapse of the pores led a long plastic plateau stress state, which improved the energy absorption and vibration damping abilities.
In fact, the initiation of gradual collapse of the brittle upper crustal prism can be inferred as due to the closure of a multitude of microfractures developed during the interseismic period above the brittle-ductile transition.
The defeat of Hugh O'Neill, 2nd earl of Tyrone, at the Battle of Kinsale in 1601 marked the start of the gradual, century-long collapse of Gaelic civilization as the dominant mode of Irish existence.
The Dutch writer Renate Dorrestein's new novel traces the gradual disintegration and final collapse of a comfortable middle-class family in the Netherlands.
And at home, the near-collapse and gradual revival of New York City.
Consequently, the structure can reach a condition of collapse because of gradual changes in its geometry.
Further shoaling could cause a gradual decline or even a collapse of large pelagic fisheries as many species will move offshore.
