Q.Weed Infestation In Gravel Driveway
Chemical weed killer has not been effective.

Certified GKH Gardening Expert
It can take some time to eradicate weeds. You may consider raking off the gravel and applying a weed barrier cloth, then putting the gravel back. Some people use flame weeders for stubborn weed problems in gravel. There are safety precautions and this may not be a solution for you, but you may want to try it. Make sure you follow all the "rules," and best of luck to you. Here's an article that will help: https://www.gardeningknowhow.com/plant-problems/weeds/what-is-flame-weeding-information-on-flame-weeding-in-gardens.htm
and another on general weed killing in gravel: https://www.gardeningknowhow.com/plant-problems/weeds/controlling-gravel-weeds.htm

I have had good success keeping weeds under control in my gravel by spraying a mixture of salt and white vinegar. There was no need for me to buy the "super strength" vinegar, I used the cheap gallon-sized vinegar available at the supermarket, mixed with about a cup of table salt in a garden pump sprayer. Squirt on weeds, they will be yellowed within hours. Best done in heat of day so they absorb the salt/vinegar. Must be careful not to spray it anywhere you want anything to grow, because it really does stop everything from growing!