<?xml version="1.0" encoding="UTF-8" standalone="no"?><?Xpress productLine="ncc-clause" ?><clause id="_d909cf05-a3a8-45b3-b53a-4f86e41eaaf4" outputclass="ncc-clause"><meta><facet building="Class 2"/><facet building="Class 3"/><facet building="Class 4"/><facet building="Class 5"/><facet building="Class 6"/><facet building="Class 7a"/><facet building="Class 7b"/><facet building="Class 8"/><facet building="Class 9a"/><facet building="Class 9b"/><facet building="Class 9c"/></meta><sptc>3.3.4</sptc><title id="_c7bf4a8d-51fc-4f1b-b76c-b011e7d89f37">Subsoil drainage</title><archive-num>2019: 3.1.3.4</archive-num><subclause id="_2fea70b4-bff4-4471-9c9f-a93f2919c3d2" outputclass="subclause"><title id="_2d5e7ce8-0f12-41b1-b055-02d0fb5bc1f0">SubClause</title><num>1</num><p>Where a subsoil drainage system is installed to divert subsurface water away from the area beneath a building, the subsoil drain must—</p><ol outputclass="alpha"><li id="_69523fb0-c4fb-46cd-b7ee-d66e4e9bc446">be graded with a uniform fall of not less than 1:300; and</li><li id="_640c492f-aeec-458d-ab17-d20e70d2b1cd">discharge into an external silt pit or sump with—<ol><li>the level of discharge from the silt pit or sump into an impervious drainage line not less than 50 mm below the invert level of the inlet (see <xref xmlns:inv="urn:xpressauthor:xpressdocument" format="dita" href="/tmp/QppServer/Publishing/5e2c1f63-e589-4ce1-95e8-5c3e286a7aff/538_0.6.0.xml#_b319692b-4779-4309-81f6-96cf89845d91" id="_ac4fd4c3-6442-48ee-9512-63913ff3c3a6" inv:access="external" referencetype="Text" scope="local" synctargettext="false" type="image-reference">Figure 3.3.4</xref>); and</li><li>provision for cleaning and maintenance.</li></ol></li></ol></subclause><image-reference conref="/tmp/QppServer/Publishing/5e2c1f63-e589-4ce1-95e8-5c3e286a7aff/538_0.6.0.xml" id="_b319692b-4779-4309-81f6-96cf89845d91"><num xmlns:inv="urn:xpressauthor:xpressdocument" inv:access="external">3.3.4</num><title xmlns:inv="urn:xpressauthor:xpressdocument" id="_efeff34c-e02b-42a3-b163-aaaf784974d2" inv:access="external">Construction of silt pits</title><image xmlns:inv="urn:xpressauthor:xpressdocument" alt="construction of silt pits" height="620" heightdpi="200" href="ERROR_IN_RESOLVING_URI:3-3-4-construction-of-silt-pits.eps" inv:access="external" width="1200" widthdpi="200"/></image-reference><callout id="_ab61e187-33d9-4d61-a5c0-dd4e1717fb6c"><callout-type ncc-info-type="info"/><p>Subsoil drainage systems may need to be installed where subsurface water movement could damage buildings or cause loss of amenity through the build up of excessive moisture or lateral water pressure. Typical locations of subsoil drainage systems are on the uphill side of cut and fill sites, adjacent to deep footings, behind retaining walls and adjacent to basement walls.</p><p>The design and installation of subsoil drainage systems should take into account the nature of the soil and the anticipated water level, quantity and movement. In some cases, detailed investigations involving excavations, field observations and soil tests may be necessary to determine the appropriate solution. Typical subsoil drain configurations are shown in <xref format="dita" href="/tmp/QppServer/Publishing/5e2c1f63-e589-4ce1-95e8-5c3e286a7aff/4375_0.7.0.xml#_a598b3ad-2165-470b-8a8d-0cc2df09670e" id="_2cedf2e5-abae-4eaa-bbb3-045eeeac4a9c" referencetype="Text" scope="local" synctargettext="false" type="image-reference">Figure 3.3.4 (explanatory)</xref>.</p><p>In clay soil, subsoil drains can alter the long-term moisture content in the soil, adversely affecting the building <xref xmlns:inv="urn:xpressauthor:xpressdocument" format="dita" href="/tmp/QppServer/Publishing/5e2c1f63-e589-4ce1-95e8-5c3e286a7aff/1315_0.7.0.xml#_8bb7272b-1ab2-45ba-9642-40b192e2393a" id="_68e2e2e7-b8b4-4829-b728-0fd435fcfaa0" inv:access="external" referencetype="Text" scope="local" synctargettext="false" type="abcb-glossentry">foundation</xref> by removing or, in some cases, introducing water. In such conditions, subsoil drains should only be used where there are no other options for dealing with subsoil water.</p><p>Additional guidance on subsoil drainage systems can be found in AS/NZS 3500.3 and AS 2870.</p><image-reference conref="/tmp/QppServer/Publishing/5e2c1f63-e589-4ce1-95e8-5c3e286a7aff/4375_0.7.0.xml" id="_a598b3ad-2165-470b-8a8d-0cc2df09670e"><num>3.3.4 (explanatory)</num><title id="_0dd05ce8-6abe-45b1-a4cb-db6686514dc8">Typical subsoil drain configurations</title><image alt="Typical subsoil drain configurations" height="906" heightdpi="200" href="ERROR_IN_RESOLVING_URI:3-3-4-explanatory-typical-subsoil-drain-configurations.eps" width="1200" widthdpi="200"><image height="906" heightdpi="200" href="C:\Users\bkiem\AppData\Roaming\Quark\XML Author\Temp\media1_fe704f74-9f8c-4107-823f-b8c2d6454446.jpg" width="1200" widthdpi="200"/></image></image-reference></callout></clause>