Canterbury Guidance - Building Performance

1 C2. FOUNDATION ASSESSMENTCCONTENTSPart C: Assessing, repairing and rebuilding foundations in TC3 Contents11. Introduction to Ove r v i ew .. General principles ..11. Scope ..11. Future Guidance for TC3 .. Future land Performance in Background .. Lateral spreading and other lateral ground movements in TC3 .. Vertical settlement in TC3 .. Geotechnical investigations in TC3 General ..13 . Single or isolated house site investigation .. Area-wide investigations .. Geotechnical investigation requirements for repaired and rebuilt foundations .. Liquefaction assessment .. Technical Category TC3 confirmation ..13 . Longevity of factual and interpretative reports ..13 . Building consent information ..13 .1114 Repairing house foundations in General ..14 . Assessment of foundation damage ..14 .115 New foundations in Foundation types and selection considerations ..15.

2 Deep piles .. Site ground improvement ..15 . Surface structures with shallow foundations .. :June 2015 DATE: APRIL 2015. VERSION: 3 a PART C. TC3 TECHNICAL Guidance CONTENTS / PAGE IC2. FOUNDATION ASSESSMENTCCONTENTSA ppendix C1: Basis for confirming compliance with the Building Code for new and repaired house foundations in Background and principal issues .. Guidance for demonstrating Building Code compliance foundation repairs and rebuilds .. General .. Engineering sign-off .. C2: Guidance on PGA values for geotechnical design in CanterburyC P ur p ose ..C Background ..C Interim Guidance on PGA values for geotechnical design ..C C3: Recommended procedure for calculating capacity for single driven piles in cohesionless Procedure for using method based on SPT Data ..C 3 . Procedure for using method based on CPT data .. C4: Method statements for site ground Construction quality and quality control.

3 C 4 . Area replacement ratio (ARR) .. Shallow foundation treatments .. Deep foundation treatments ..C 4 . Crust reinforced with inclusions ..C 4 . Target CPT tip resistances for ground improvement .. :June 2015 DATE: APRIL 2015. VERSION: 3 a PART C. TC3 TECHNICAL Guidance CONTENTS / PAGE IIC2. FOUNDATION ASSESSMENTCCONTENTSF iguresFigure : Simplified cross-section showing components of lateral ground movement (values illustrative only).. : Overview of general geotechnical investigation required .. : Overview of process for repairing foundations on TC3 sites for Foundation Types A and B .. : Overview of process for repairing foundations on TC3 sites for Foundation Type C .. : Perimeter foundation wall detail for TC3 .. : General process flowchart for new and rebuilt foundations in TC3 (for sites with Minor to Moderate lateral ground movement) .. : Deep pile suitability summary (concrete or timber floor).

4 : Pile head detail timber .. : Pile head detail steel ..15 .10 Figure : Pile head detail concrete ..15 .11 Figure : Illustrative pile layout for a flat concrete slab .. : Section A-A Illustrative pile layout for a flat concrete slab ..15 .16 Figure : Illustrative layout and sample details for a waffle slab on deep pile ..15 .16 Figure : Sample detail for a waffle slab on deep pilesFigure : Densified Raft excavate and recompact (Type G1a) (left) and Rapid Impact Compaction (Type G1c) (right) .. : Reinforced Crushed Gravel Raft (Type G1d) .. : Reinforced Cement Stabilised Crust (Type G2a) .. : In situ Cement Stabilisation (Type G2b) .. : Deep Soil Mixed Columns (Type G3) .. : Stone Columns (Type G4) .. : Composite Shear Wave Velocity Measurement .. : Shallow Stone Columns (Type G5a) .. : Driven Timber Piles (Type G5b) .. : Horizontal Soil Mixed Beams.

5 : Plan of Type 1 surface structure .. : Perimeter foundation details for Type 1 surface structure .. : Plan of Type 2 surface structure .. : Section through Type 2A surface structure at the timber piles .. : Detail of Type 2A surface structure at the timber piles (including gravel raft) .. : Section through Type 2B surface structure at the timber piles (including gravel raft) .. : Detail of plywood stiffening to Type 2 surface structure (Type 2A illustrated) .. : Plan of Type 3A surface structure .. : Type 3A surface structure - Detail at supporting blocks .. : APRIL 2015. VERSION: 3 a PART C. TC3 TECHNICAL Guidance CONTENTS / PAGE IIIC2. FOUNDATION ASSESSMENTCCONTENTSF igure : Plan of Type 3B surface structure .. : Type 3B surface structure Section through pre-stressed concrete support beam and beam connection .. : Cross-hole shear wave velocity testing of Type G5 ground improvement.

6 : Equivalent target soil densification criteria for all soils .. : Target soil densification criteria for clean sand .. : Global lateral movement categories for TC3 (at ULS) .. : Areas of major global lateral ground movements identified within TC3 to date .. : Distance from free edge beyond which minor to moderate global lateral movement can be assumed in TC3 (excluding areas in Table ), in the absence of any evidence to the contrary .. : Categories of lateral stretch of the ground across a Building footprint for TC3 (at ULS) .. : Categories of vertical land settlement (index values at SLS) .. : Summary relationship between likely final investigation densities and foundation types .. : Overview of proposed TC3 foundation types ..15 .1 Table : Overview of floor and foundation types for new and rebuilt foundations (a) Deep : Overview of floor and foundation types for new and rebuilt foundations (b) Site ground improvement and surface structures.

7 : Typical pile sizes and indicative capacities .. : Summary of ground improvement types covered by this Guidance document1 (grouped by construction methodology) .. : Surface structure capability summary .. : Shallow foundation solution alignment Vertical settlement .. : Shallow foundation solution alignment Lateral stretch .. : Interim recommendations for PGA values for geotechnical design in Canterbury (for a design event) .. : APRIL 2015. VERSION: 3 a PART C. TC3 TECHNICAL Guidance CONTENTS / PAGE IVC2. FOUNDATION ASSESSMENTC11. INTRODUCTION11. Introduction to OverviewThe Guidance provided in Part C focuses on foundation repairs and reconstruction for houses in Foundation Technical Category 3 (TC3) areas within the Green Zone of the earthquake-affected parts of the Canterbury region. It does not apply to the Residential Red Zone where significantly poorer ground conditions exist and more severe land damage is expected in future earthquakes.

8 Land that has been classified as TC3 in the Green Zone has a higher probability of being at some risk of moderate to significant land damage from liquefaction in future large earthquakes. Specific geotechnical investigations are required to check the likely land Performance . Where the TC3 classification is confirmed by investigation, specific engineering design will often be required for the repair or rebuilding of foundations in this technical category. Part C must be read in conjunction with Parts A and B of the Guidance . Material from Parts A and B is only repeated where considered necessary. Intended audienceThis Guidance is intended for the engineering design, construction and insurance sectors, local authorities, and their professional advisors and contractors to clarify the technical and regulatory requirements for TC3 land. Given that most foundation repairs and reconstruction in TC3 require specific engineering input, the principal users of this document will be professional geotechnical and structural regarding the scope of repairs and rebuilding residential dwellings in Technical Category 3 are complex, and are much more reliant on engineering judgement than the other technical categories.

9 Specific input from Chartered Professional Engineers (geotechnical and structural, as appropriate) is therefore the solutions included in the Guidance have not yet been fully prototyped, it is expected that the Guidance will need refinement with experience. It is also likely that other solutions and analytical tools will be developed during the repair and rebuilding process that can be incorporated into future versions of this Guidance . Future updates will be available online from the Ministry s website and rebuilding strategies and decisions will be influenced by insurance contracts and the decisions made by the parties to those contracts. The engineering considerations and criteria outlined in this document are intended to provide input into those :December 2012 UPDATE:December 2012 DATE: APRIL 2015. VERSION: 3 a PART C. TC3 TECHNICAL Guidance INTRODUCTION / PAGE FOUNDATION ASSESSMENTC11. General principlesPart C of the Guidance has been prepared based on a series of general principles.

10 These principles have guided the development of the document, and are set out below to assist engineers in the interpretation and implementation of the proposed solutions for individual TC3 sites, and for situations where other solutions are formulated. Underlying principles1. Guidance in the document is based on current knowledge, and represents best practice advice prepared by the Ministry, drawing on the expertise of a range of highly experienced New Zealand and international geotechnical and structural Guidance will be updated as new technical information, experience from built solutions, and field test results become available. 2. The potential for land damage from liquefaction on the plains in Canterbury represents a complex continuum - from residential Red Zone areas being vacated where there are saturated loose, unconsolidated silts and sands close to the surface (often in combination with proximity to unrestrained free edges), through areas of more moderate damage potential, to areas that are considered to be of relatively low damage potential designated as TC1.