8 Execution (p. II)
8.3 Preliminary works
8.3.1 A stable and dry working platform should be provided.
8.3.2 The position of each jet grouting hole shall be accurately located and identified.
8.3.3 A system of collection and disposal of the spoil return should be provided.
8.3.4 For horizontal treatment measures to maintain the stability of the working face shall be taken.
8.3.5 The design assumptions concerning the geometry and structural condition of nearby structures shall be accurately verified before the jet grouting works are carried out.
8.4.1 Drilling can be performed with air or water or muds or grouts or foams as flushing media. If required casing is used.
8.4.2 Where the borehole is unstable, or there is significant drill fluid loss, or where the soil conditions are otherwise likely to unduly inhibit spoil return, suitable preventative measures shall be adopted.
8.4.3 The deviation of the drilling starting point from the theoretical position shall be less than 50 mm, if not otherwise stated by the design specifications.
8.4.4 The deviation of drilling from the theoretical axis should be 2 % or less for depths up to 20 m. Different tolerances should apply for greater depths and for horizontal jet grouting.
8.4.5 The annular space between the drilled hole and the jet grouting string should be sufficient to permit a free flow of the spoil return to the borehole collar.
8.4.6 Where unexpected underground obstructions are encountered, appropriate measures should be taken, in order to avoid undesirable effects in the jet grouting phase.
8.5 Jet grouting
8.5.1 Jet grouting shall be executed and supervised by trained and experienced personnel.
8.5.2 For the panel method, the direction of adjacent elements should deviate from the average plane to facilitate the connection between the panels and consequently the continuity of the wall.
8.5.3 For the panel method, the orientation of the jetting nozzles shall be accurately controlled.
8.5.4 When bleeding is critical for jet grouting, the contact zone with the surrounding soil or structure should be verified.
8.5.5 In underpinning applications measures shall be taken to ensure that a final intimate contact is formed between the top surface of the jet grouted column and the underside of the foundation.
8.5.6 Jet grouting should be executed with a sufficient thickness between the upper nozzle and the ground surface, to avoid possible local hydrofracturing.
NOTE The above thickness may vary from 0,5 m for vertical boreholes to 2,0 m for horizontal boreholes and can be reduced in the presence of an adequate restraint to the surface, such as a slab or a wall.
8.5.7 For horizontal jet grouting the collar of the borehole shall be plugged as soon as jet grouting is completed.
8.5.8 When jet grouting an element is interrupted for any reason, the re-start shall be undertaken using procedures that are intended to ensure the continuity of the element.
8.6 Spoil Return
8.6.1 During jet grouting a visual observation of the flow and features of the spoil return at hole collar shall be maintained.
8.6.2 Further control may be achieved by measurement of specific physical or chemical properties of the spoil return.
8.6.3 If during the jet grouting unexpected behaviour of the spoil return is observed, the jet grouting parameters and/or method should be reviewed.
8.6.4 An unexpected reduction in spoil return shall be investigated and dealt with immediately. It can be caused by clogging of the annulus of the jetting borehole.
8.7 Placing the reinforcement
Reinforcement can be installed in the fresh jet grouted material during or immediately after the completion of the jet grouting operations. Alternatively it can be installed in a borehole drilled into the element after hardening.