CHAPTER 13 - MECHANICALLY STABILIZED EARTH WALLS AND PATENTED EARTH RETAINING SYSTEMS DS Temple 13.1 SCOPE This section covers the inspection of mechanically stabilized earth walls and other patented earth retaining systems as per the applicable chapter of the Specifications. It also covers the special attention which must be given by the engineer s monitoring staff to the specific requirements of setting out, excavations, backfilling, foundations, precast concrete elements, reinforcing slopes and the erection of wall panels. 13.2 PATENTED EARTH RETAINING SYSTEMS The engineer s monitoring staff should obtain from the patent holder of such systems the checklists and other Quality Assurance documentation before commencement of the construction. The monitoring staff should ensure that the work is carried out and signed off in accordance with the requirements of the specific system and the applicable Specifications. 13.3 INSPECTIONS Inspections in accordance with the Manufacturers Check Lists should be carried out relating to: 13.3.1 Excavations Excavations for patented earth retaining systems are generally not very deep and are more related to leveling the site so that the wall foundations (leveling pads) are stepped to form a base for the wall. The dimensions and levels of these excavations are therefore important to ensure that the precast elements can be constructed properly to line and level. Compaction of the existing material or imported foundation fill to the requirements of the design should be verified. 13.3.2 Foundations (Leveling Pads) Verify the foundation or leveling pad elevations. Ensure that formwork, reinforcement and concrete (Class) is carried out in accordance with the specifications. Where no period is specified for the foundation concrete before wall elements are placed, a minimum of 3 days curing time is required. It is important to have a high quality of surface finish on the top of the foundations to ensure that the wall elements are erected to line and level. Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-2
13.3.3 Precast Concrete Panels and Blocks Photo 13.1: Correct leveling pad These panels and blocks are usually manufactured in a factory to stringent quality assurance systems. The engineer s monitoring staff should however ensure that the elements have been cast to the dimensions required on the drawings. The concrete strengths of the panels / blocks must be verified by factory QA records to ensure that the panels / blocks are fit for purpose. The monitoring staff should make at least one factory inspection during the period that concrete elements are being manufactured for the project. Reject all panels / blocks that do not comply with the drawings and specifications. Photo 13.2: Correct panel storage Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-3
13.3.4 Backfill The engineer s monitoring staff should check that the quality of the backfill material conforms to the Project and Standard Specifications. The type, quality and compaction of the backfill are important factors in the overall design of the wall and these aspects are of critical importance to each of these patented systems. Photo 13.3: Correct backfilling Compaction within two metres behind the retaining wall systems should be carried out to the specified density using only hand operated compactors. Compaction of backfill in front of the wall should be carried out in a similar manner to prevent washaways during rainy conditions as movement in the leveling pad will adversely affect the performance of the wall. 13.3.5 Reinforcing Strips Photo 13.4: Within 2m of the panels, only small rollers may be used The engineer s monitoring staff should ensure that the size and grade (length and thickness) of the reinforcing materials are in accordance with the drawings and specifications. Good site housekeeping practices should be adhered to for the storage and handling of all elements required for the construction of the wall. These measures must at least meet the requirements of the manufacturer / supplier. Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-4
Photo 13.5: Correct storage of reinforcement strips 13.3.6 Erection of Panels / Blocks Photo 13.6: Unacceptable storage and backfilling The engineer s monitoring staff should ensure that each layer of panels or blocks is adjusted to line and level prior to the construction of the subsequent layer. Only wooden wedges should be used so that panels / blocks do not spall. The wedges should be removed timeously as the wall progresses in height, otherwise they become difficult to remove after more than 3 levels are supported on them. It is very important that vertical walls be constructed with a slight tilt to the inside in accordance with the design so that the wall is vertical after construction. Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-5
13.4 TESTING REQUIREMENTS Photo 13.7: Correct wedge placing (2 rows are adequate) The engineer s monitoring staff should ensure that the materials hereunder are tested in accordance with the specifications. 13.4.1 Backfill Patented earth retaining systems require that a zone of backfill behind the retaining wall system is constructed using a very specific quality of material and is compacted to a given density. Monitoring staff should ensure that the number and frequency of tests are adequate to ensure compliance. 13.4.2 Reinforcing Strips The supplier of the various types of reinforcing strip should supply all relevant test certificates to cover the batches of materials used to manufacture the strips and fasteners. 13.4.3 Panels / Blocks Where precast concrete panels are constructed on site the requirements of the Specifications should apply. Where elements are supplied from commercial sources the supplier should supply Quality Assurance data and certificates to verify compliance with his specifications. Random checks related to cover, strength, etc. should be carried out as required on site. Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-6
INDEX TO APPENDICES 13A - MECHANICALLY STABILIZED EARTH WALLS AND PATENTED EARTH RETAINING SYSTEMS Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-7
CONSTRUCTION MONITORING CHECKLIST APPENDIX 13A CONSTRUCTION MONITORING CHECK LIST (1/2) PROJECT NO. / NAME:... INSPECTOR S NAME(S):... STRUCTURE:... ELEMENT:... ACTIVITY AND DETAILS 1. FOUNDATION PREPARATION 1.1 R.E. wall setting out 1.2 Compaction to specified density 1.3 Confirm allowable bearing pressure 1.4 Foundation Fill 2. DRAINAGE SYSTEM 2.1 Drainage installed as per drawing 3. LEVELING PAD 3.1 Excavation of leveling pad area 3.2 Leveling pad set to the proper vertical elevation and horizontal alignment per drawings (elevation tolerances +3 mm to -6 mm) 3.3 Leveling pad cured for a minimum of 24 hours 3.4 Horizontal lift between step-up pads 4. PANEL ERECTION 4.1 Confirm correct panels used 4.2 Confirm correct clamps and bracing in place (initial course only) 4.3 Confirm panel batter 4.4 Confirm correct placement of wooden batter wedges 4.5 Confirm correct joint spacing 4.6 Confirm vertical and horizontal alignment every 10 panels 4.7 Wooden wedges removed after full erection of the upper panel 4.8 Confirm wall vertical alignment for each additional row of panels 5. JOINT MATERIALS 5.1 Filter fabric placed correctly to cover horizontal and vertical joints 5.2 Bearing pads placed in panel grooves APPROVAL SIGNED DATE Y/N N/A Comment Check list continues on next page Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-8
APPENDIX 13A CONSTRUCTION MONITORING CHECK LIST (2/2) ACTIVITY AND DETAILS APPROVAL Y/N N/A Comment SIGNED DATE 6. REINFORCING STRIPS 1.1 Are reinforcing strips properly galvanized 1.2 Are reinforcing strips placed to correct lengths and number per drawings 1.3 Are straps are placed perpendicular to the wall or skewed per drawings 1.4 Is the placement of connections, bolt, washer and nut correct 1.5 Are splices of correct length 7. BACKFILLING 7.1 Quality of selected backfill material 7.2 Loose backfill thickness not to exceed 250 mm 7.3 Compacted backfill 50 mm above tie strip level 7.4 Backfill to slope 300 mm behind first layer of each row of panels 7.5 Compaction within 900 mm of the back face with suitable compaction equipment as specified 7.6 Confirm backfill placed parallel to the wall panels 7.7 Backfill testing frequency of one test for each lift and every 15m length of wall 7.8 Confirm backfill compaction to 95% Mod AASHTO density Mechanically Stabilized Earth Walls And Patented Earth Retaining Systems 13-9