Garlic powder in a small BEACH vignette????

KAYSEE88

Can i use garlic powder for the 'sand'? 

No.  Do not use food products.  As mentioned above, they can draw bugs, and they will decay and moulder with time.

In addition to the products suggested above, I'll recommend having a look at Woodland Scenics products, too.  That brand is popular among model railroaders, but the products can be very useful to us scale modelers, too.  You can find them online with a web search, but they are also sold at the craft store chains Michael's and AC Moore, too.  Also, if there is any shop near you that caters to model railroaders, they should have Woodland Scenics products.

KAYSEE88

How do i create tire marks?

I'm not being a smart-aleck, but, use a tire.  Use one of the kit tires, before you attach it, or if you've accumulated a parts stash, use one from there.

KAYSEE88

...and how to add shadows to them after?

You can use washes and weathering powders to give the tire ruts some shadow and emphasize them.  There are a lot of products available, such as those from AK Interactive or Tamiya.  I make my own washes, using craft-store acrylic paints thinned with water.  And I make my own weathering powders using pastel chalks that I grind myself.  The commercial products do take the guesswork out of making those things, though, if you've never done it before.

Hope that helps!

Best regards,

Brad

Actually,,Chinchilla dust is your best bet.  I use it all the time in my dioramas.

https://www.google.ca/search?q=chinchilla+dust&sxsrf=ACYBGNQLpYEIzjBcty2BTxunfz3KaAezBw:1575118440098&source=univ&tbm=shop&tbo=u&sa=X&ved=2ahUKEwiEqOe4_ZHmAhWjm-AKHTN-BvYQsxh6BAgNECw&biw=1536&bih=846

I have had some luck using tan tile grout to represent sand.  Stays put and is easily painted.  Seeing what happens to the garlic powder in my kitchen, I would be afraid that humidity would change its composition and color in time.

There is a fine grained pet bird gravel available which can be used.

Hi;

 Oh Gosh! Don't use Garlic Powder. There is a sand style stuff used in " N " ( 1/160) train layouts that is better. Use that .You can wet the tires and roll them in the material when it's about half dry.

I'd suggest not using anything organic, bugs will eat it, even if fixed using some kind of adhesive/binding agent. If the bugs don't  eat it, humidity/moisture  may cause it to decay. Definitely not a good idea. 

Try a plaster base and dust with ground up pastels or chalk sticks.