log4net logging threadcontext

i have log4net controlling asp.net site. i'm means record messages db table, nonetheless isn't logging threadcontext properties. example:

threadcontext.properties["url"] = httpcontext.current.request.url.tostring();
threadcontext.properties["httpreferer"] = httpcontext.current.request.servervariables["http_referer"];

my log4net.config adds those values parameters sql db table:

<parameter>
    <parametername value="@url"/>
    <dbtype value="string"/>
    <size value="512"/>
    <layout type="log4net.layout.patternlayout">
        <conversionpattern value="%property{log4net:url}"/>
    </layout>
</parameter>
<parameter>
    <parametername value="@httpreferer"/>
    <dbtype value="string"/>
    <size value="512"/>
    <layout type="log4net.layout.patternlayout">
        <conversionpattern value="%property{log4net:httpreferer}"/>
    </layout>
</parameter>

as i debug, i those threadcontext properties being set, nonetheless aren't removing db.

how i work?