The gravel texture has weird darkness which is based on the mesh. Do you why this happens?
There is a displacement texture and I added subdivision surface. After this, the weird dark lines are occured. Here is the blender file which also included textures: https://1drv.ms/u/s!Ao1sZAH1uraLg7B1jIxW6Wlbxah25Q?e=XiDvIW
The Problem:
Your mesh has terrible geometry as @duarte had mentioned in the comments. All you have to do is fix the geometry of your plane by following the GIFS given below. It's best if you start from scratch by adding a new plane into your scene as your old plane has several problems for example bad geometry and it's huge in size.
You can fix this with four simple steps in which two steps are optional
Your mesh`s UV unwrap vs The new modified one(Comparison):
Solution:
STEP 1:
First, add a new plane to your scene, tab into edit mode, press 'A' to select all faces, left-click in face select mode, select the 'subdivide' option then repeat subdividing the plane 5 times. Now press 'C' to have the circle selection mode enabled(left click to disable), select a few faces that resemble a jagged-edged circle. Make sure that you have selected them symmetrically. Last but not least press 'X' to delete the faces
STEP 2:
Select all the edges of the jagged-edged circle, press 'Shift+Alt+S' on your keyboard for the 'To sphere' tool and then drag.
STEP 3:(optional)
Press the 'add new shader' option, then add a 'Texture coordinate' node and a 'Checker Texture' by pressing 'Shift+A', connect the checker textures 'colour' to the Principled BSDF's base colour and connect the 'UV' of the texture coordinate to the 'vector' of the checker texture. We added this so we can check at how the mesh`s UVs look like.
STEP 4 (optional):
Go to the 'UV editor',tab into edit mode,select all the faces,press'U',select unwrap and scale the unwrap in the UV editor.
By the way it's not compulsory that you should create a new checker texture. I just created it to show you how the UVs looks like. You can go ahead and skip those steps and directly add the original texture you added to your old plane(the one without the good geometry).
