If you want to sort on DB ( not on application ), then

use patindex() and substring() functions to extract the integer part of your column( considering null cases as zero ), and then cast as integer :

Order By cast( coalesce(
                substring(yourCol, patindex('%[0-9]%', yourCol), 
                   patindex('%[0-9][^0-9]%', yourCol + 't') 
                   - patindex('%[0-9]%', yourCol) + 1)

               ,0)  as int )

within your select statement.

Demo

How about this SQL:

SELECT MyStringField,
       (CASE WHEN ISNUMERIC(MyStringField) = 1 THEN Cast(MyStringColumn as int) ELSE 999999999 END) MyNumericField
FROM MyEntity
ORDER BY MyNumericField, MyStringField

See also: How do I sort a VARCHAR column in SQL server that contains numbers?

I used the following C# snippets in order to get this behavior:

DataContext:

modelBuilder.Entity<MyEntity>().Property(s => s.MyNumericField).HasComputedColumnSql("CASE WHEN ISNUMERIC([MyStringField]) = 1 THEN Cast([MyStringField] as int) ELSE 9999999999999 END");

MyEntity:

public class MyEntity
{
  //...
    [Required]
    public string MyStringField
    {
        get;
        set;
    }

    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public decimal MyNumericField
    {
        get;
        set;
    }
  //...
}

Linq query:

var result = await query.OrderBy(x => x.MyNumericField).ThenBy(x => x.MyStringField).ToListAsync();