Codeigniter select query with AND and OR condition

$where = '(doctor_slot.day_name="'.date('l', time()).'"
OR doctor_slot.day_name="'.date('l', strtotime('+1 day')).'"
OR doctor_slot.day_name="'.date('l', strtotime('+2 day')).'")';

$this->db->where($where);

 $this->db->where('wrk_fld_exc',140);
       $this->db->where('wrk_cs_sts','open');
       $where = '(wrk_dlvrd_sts="open" or wrk_cl_sts = "Success")';
       $this->db->where($where);