Windows:
cmd> svnadmin dump c:\repo\proj1 > c:\proj_backup\proj1_date
Equivalent Linux command:
shell> svnadmin dump /repo_path/proj1 > /backup_path/proj1_date

Then I created a test repository and imported the backup file to the new test repository to see whether it is working. After that I deleted the test repository.

Windows command:
cmd> svnadmin create c:\repo_path\proj1_new
cmd> svnadmin load c:\repo_path\proj1_new < c:\proj_backup\proj1_date
cmd> rmdir /s c:\repo_path\proj1_new
Equivalent linux command:
shell> svnadmin create /repo_path/proj1_new
shell> svnadmin load /repo_path/proj1_new < /proj_backup/proj1_date
shell> rm -rf /repo_path/proj1_new

Then I created a zip copy of the backup file proj1_data to proj1_date.zip and imported the zip copy to my account of assembla. This is how I solved the problem related to backup & restore my project repository. Subversion_Tutorial is a nice SVN site for quick reference.