To preserve file extension:
<log4net>
<root>
<level value="DEBUG"/>
<appender-ref ref="RollingLogFileAppender"/>
</root>
<appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
<file type="log4net.Util.PatternString" value="D:\\LogFolder\\%date{yyyyMM}\\SchT.log" />
<appendToFile value="true" />
<rollingStyle value="Date" />
<maximumFileSize value="30MB" />
<staticLogFileName value="true" />
<preserveLogFileNameExtension value="true"/>
<datePattern value="ddMMyyyy" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger - %message%newline" />
</layout>
</appender>
</log4net>