Higher thrust engines

[canuck slf]

Several days ago a few of us civil engineering types working at an airport were discussing a recent accident involving an engine run up in an unauthorized location damaging a 767 tail. This led onto a review of damages caused by ever more powerful engines ripping up asphalt on runways, either due to the outboard engines being over the shoulder, or the thrust being directed downward at rotation.
My question is: Are the more recent and future engines getting increased thrust from higher exhaust velocity, or moving more air at the same speed?
The reason for asking is that we must get to a point at which asphalt surfaces built up in layers are unable to withstand the blast, a problem which should not occur with a concrete surface.

Thanks in advance.

Regards

[Mad (Flt) Scientist]

Noise regs will generally drive engines towards more massflow rather than higher jet velocities, since high spped efflux is a major source of noise. So I would say that most thrust increase is coming from larger massflow.

[rwm]

I remember a similar incident happening to a Canadian Airlines jet, in Vancouver. I think it was atrributed to poor building methods and material on the appron. Partly because some of the airport is built on marsh and what once was water.

As to sound, the lower velocity the less noice. Older engines use mixing lobes to mix the hot core flow with fan air to slow the speed of the jet blast, and lower the noise output. More modern engines have larger fans, and smaller cores with more shafts to make the engines smaller, and to control speeds of the rotating cores.