Hard to pinpoint the issue but here are some steps that might solve this glitch:
- Verify integrity (should go without saying).
- Delete /bin/ folder in your W3 directory, then verify. It'll redownload a lot of stuff. That used to fix a lot of patch-induced bugs.
- Check GPU drivers, rollback them to earlier stable version.
- Physically remove your GPU, dust off the socket and connectors.
For certain that's not a RAM issue. It's not the power of your card either. People have ran this game on ancient rigs with graphics modded to look like PS1 without such glitches.
It's either a) game files issue, since ground textures are missing (not super popular, but a known occasional bug) b) driver issue c) graphics card issue. Cards get old. Artifacts are a sign of old age.
I recommend the order I suggested, as it is from least intrusive to most intrusive. Also, it's logical to fix gamefiles to brand new before starting to mess with GPU drivers/GPU itself.