Here is how to do it:

1. place your log4net.config file in root directory

2. modify Global.asax.vb file > Application_Start method

  Private Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)

            If Config.GetSetting("ServerName") = "" Then

                ServerName = Server.MachineName

            Else

                ServerName = Config.GetSetting("ServerName")

            End If

Dim path as String = HttpContext.Current.Server.MapPath("~/log4net.config")

If  File.Exists(path) Then

                log4net.Config.XmlConfigurator.ConfigureAndWatch( new FileInfo(path))

End If

        End Sub

That is it. You can start logging or looking at the logs of let's say NHibernate