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Be very careful of AS2870-2011

Be very careful of AS2870-2011

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Be very careful of AS2870-2011

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  1. Be very careful ofAS2870-2011 Scott Warner

  2. OBJECTIVES: • Site Classification • Footing Selection

  3. Part 1 Is it a soil classification? Or Is it a site classification?

  4. SECTION 3 STANDARD DESIGNS3.1 SELECTION OF FOOTING SYSTEMS 3.1.1 Selection procedure Standard deemed-to-comply designs shall be in accordance with Clauses 3.2 to 3.6. These designs shall not apply to – • Class E or Class P sites:

  5. 2.1.3 Classification of other sites Sites with inadequate bearing strength or where ground movement may be significantly affected by factors other than reactive soil movements due to normal moisture conditions shall be classified as Class P. Class P sites include ......... reactive sites subjected to abnormal moisture conditions.....

  6. 2.1.3 Classification of other sites A site shall be Class P if – • The bearing strength is less than that specified in Clause 2.4.5; • Excessive foundation settlement may occur due to loading on the foundation; • The site contains uncontrolled or controlled fill as identified in Clause 2.5.3; • The site may be subject to mine subsidence, landslip, collapse activity or coastal erosion; • The site may be subject to moisture changes due to site conditions more severe than the normal site conditions described in Clause 1.3.2; or • The site may be subject to other factors resulting in foundation movement beyond the reactive soil movements resulting from moisture changes due to the normal site conditions described in Clause 1.3.2. The basis for classification shall be recorded on the site classification report together with recommendations for further geotechnical investigation.

  7. 1.3.2 Normal sites Normal sites are those that are classified as one of Classes A, S, M, H1, H2 and E in accordance with Section 2 of this standard and where foundation moisture variations are those caused by seasonal and regular climatic effects, effect of the building and subdivision, and normal garden conditions without abnormal moisture conditions.

  8. 1.3.3 Abnormal moisture conditions Abnormal moisture conditions are those that result in foundation moisture variations beyond those for normal sites. Buildings constructed on sites subject to abnormal moisture conditions have a higher probability of damage than those described in Clause 1.3.1.

  9. 1.3.3 Abnormal Moisture Conditions • Prior to Construction • During Construction • After Construction

  10. Examples of abnormal moisture conditions existing prior to construction include the following: • Removal of an existing building or structure likely to have significantly modified the soil moisture conditions under the footprint of the footing system of the building. • Removal of trees prior to construction. • Presence of trees on the building site or adjacent site. • Unusual moisture conditions caused by drains, channels, ponds, dams, swimming pools, effluent disposal areas or tanks, which are to be maintained or removed from the site.

  11. Examples of abnormal moisture conditions resulting from construction include the following: • Failure to provide adequate site drainage. • Failure to detail or construct drainage in accordance with this Standard.

  12. Examples of abnormal moisture conditions developing after construction include the following: • The effect of trees too close to a footing. • Excessive or irregular watering of gardens adjacent to the building. • Failure to maintain site drainage. • Failure to repair plumbing leaks. • Loss of vegetation from near the building.

  13. Page 5 6.2 SITE CLASSIFICATION The results of laboratory testing indicate that the site soils have shrink/swell index (Iss) values ranging from 1.1% to 5.6%. The laboratory test results indicate that the materials encountered at the site are moderately to highly reactive. On the basis of the soil profiles encountered during field investigations, laboratory testing and preliminary calculations, the allotments in their current condition are classified in accordance with AS2870-1996 as follows: Lots 1 – 14 inclusive, Class H, Highly Reactive Lots 15 – 19 inclusive, Class M, Moderately Reactive Lots 20 – 25 inclusive, Class H, Highly Reactive Lots 26 – 42 inclusive, Class M, Moderately Reactive The effects of changes to the soil profile by additional cutting and filling and the effects of past and future trees should be considered in the selection of the design value for differential movement. Footings for the proposed development should be designed and constructed in accordance with the requirements of AS2870. Where fill is to be placed to raise site levels, the affected allotments will require reclassification once the depth and type of placed fill are known and the level of earthwork control has been established.

  14. The GeotechEngineers’s Handover: “The effect of changes to the soil profile by additional cutting and filling and the effects of past and future trees should be considered in the selection of the design value for differential movement.”

  15. Which lot is yours? Confirm the lot numbers in the geotechnical report are the same as the lot numbers on the current DP.

  16. Page 5 6.2 SITE CLASSIFICATION The results of laboratory testing indicate that the site soils have shrink/swell index (Iss) values ranging from 1.1% to 5.6%. The laboratory test results indicate that the materials encountered at the site are moderately to highly reactive. On the basis of the soil profiles encountered during field investigations, laboratory testing and preliminary calculations, the allotments in their current condition are classified in accordance with AS2870-1996 as follows: Lots 1 – 14 inclusive, Class H, Highly Reactive Lots 15 – 19 inclusive, Class M, Moderately Reactive Lots 20 – 25 inclusive, Class H, Highly Reactive Lots 26 – 42 inclusive, Class M, Moderately Reactive The effects of changes to the soil profile by additional cutting and filling and the effects of past and future trees should be considered in the selection of the design value for differential movement. Footings for the proposed development should be designed and constructed in accordance with the requirements of AS2870. Where fill is to be placed to raise site levels, the affected allotments will require reclassification once the depth and type of placed fill are known and the level of earthwork control has been established. “Please design slab systemfor Lot 16.The site is Class M.”

  17. Class P Site:

  18. Class P Site:

  19. Class P Site:

  20. Class P Site:

  21. Class P Site:

  22. Class P Site:

  23. Class P Site:

  24. Class P Site:

  25. Class P Site:

  26. Class P Site:

  27. Class P Site:

  28. What is a “Normal” site?

  29. Normal Site (Maybe?):

  30. Normal Site (Maybe?):

  31. Site Classification: The site classification should identify the site as either: • A Normal Site (& it will remain a Normal Site) or • A Class P Site. A Normal Site, can be classified as Class A, S, M, H1, H2, or E. The reasons for a Class P need to be stipulated. For a Class P Site, either: • Provide advice for an equivalent level of reactivity to satisfy the reasons that the site is Class P. “The site is Class P (because) and we recommend Class H1 slabs and footings..”. Or, • Provide the technical information sufficient for the design engineer to select or determine a suitable footing system.

  32. Part 1 Summary: • Misleading simplicity of AS2870-2011. • Standard deemed-to-comply designs only apply to Normal sites. • Most sites are not Normal, but are Class P. • Site Classification needs to recognize the factors affecting the site.

  33. Part 2 What have they done to my slab design?

  34. How much movementdo I design for?

  35. Design Procedure • Calculate Ys. • Modify Ys to account for any cutting and/or filling of the site. • Calculate Yt. • Either select a standard deemed-to-comply design, or • Use engineering principles.

  36. Newcastle Site • Natural Site, ys = 35 – 40mm (Class M) • Cut & Controlled Fill ys = 35 – 60mm (Class H1) • Cut & Uncontrolled Fill ys = 25 – 60mm (Class H1)

  37. Geographical Effects: • Newcastle Site Cut & Controlled Fill, ys = 25-60mm Class H1 • Maitland Site Cut & Controlled Fill, ys = 50-80mm Class E • Muswellbrook Site Cut & Controlled Fill, ys = 55-100mm Class E-D

  38. Changes to AS2870-2011: • Hs values have increased and vary with location • Cutting and Filling will increase ys • Calculate ys as part of every design

  39. Effect of Trees • AS2870-2011 Appendix H • New requirements