mysql - Laravel - Column name with _ returning a t_lnumber error -

my database schema has following column names:

1_1, 1_2, 1_3 etc... 

within controller, trying add these columns, it's returning following error:

syntax error, unexpected '1' (t_lnumber), expecting identifier (t_string) or variable (t_variable) or '{' or '$' 

the line @ it's occurring is:

  $audit->1_1 = input::get('1_1'); 

the full snippet of code below:

public function postaddfullaudit()   {     $audit = new audit();     $audit->site_id = input::get('site_id');     $audit->1_1 = input::get('1_1');     $audit->1_2 = input::get('1_2');     $audit->1_3 = input::get('1_3');     $audit->1_4 = input::get('1_4');     $audit->1_5 = input::get('1_5');     $audit->save(); } 

any hugely appreciated.