I always use the code below to configure log4net from code. Works great!
Hierarchy hierarchy = (Hierarchy)LogManager.GetRepository();
hierarchy.Root.RemoveAllAppenders(); /*Remove any other appenders*/
FileAppender fileAppender = new FileAppender();
fileAppender.AppendToFile = true;
fileAppender.LockingModel = new FileAppender.MinimalLock();
fileAppender.File = Server.MapPath("https://stackoverflow.com/") + "log.txt";
PatternLayout pl = new PatternLayout();
pl.ConversionPattern = "%d [%2%t] %-5p [%-10c] %m%n%n";
pl.ActivateOptions();
fileAppender.Layout = pl;
fileAppender.ActivateOptions();
log4net.Config.BasicConfigurator.Configure(fileAppender);
//Test logger
ILog log =LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
log.Debug("Testing!");