9 Supervision, testing and monitoring (p. I)

9.1 General

9.1.1 The following characteristics of jet grouted elements should be monitored for control purposes:

  • — geometry;

and, where appropriate:

  • — strength, deformability, permeability or density of the jet grouted material.

9.1.2 It is generally impractical or impossible to measure the dimensions and material properties directly on a statistically significant number of jet grouted elements.

9.1.3 The minimum quality control of jet grouting shall consist of reporting the jet grouting parameters and observing the spoil return on all elements.

9.1.4 It may be assumed that in comparable soil conditions the same jet grouting parameters produce the same element dimensions, properties and spoil return.

9.1.5 In jet grouting works, after the first few elements have been produced, measures of the dimensions and material properties should be taken on a limited number of elements to establish the relationship between the jet grouting parameters and the element properties.

9.1.6 Where comparable experience (as defined by ENV 1997-1:1994 - clause 1.5.2.) on the same jet grouting system in similar ground conditions is available, testing after execution may be omitted, if the design specifications do not require it and provided that monitoring of jet grouting parameters is applied to the jet grouted elements of the work.

9.2 Preliminary tests

9.2.1 Where comparable experience is not available, an appropriate preliminary field test shall be designed and performed. It shall cover all relevant conditions likely to be encountered on the site, in order to:

  • — enable a selection of the most effective system and jet grouting parameters;
  • — verify that the results conform to the design requirements using the selected system and jet grouting parameters.

9.2.2 Where preliminary tests are performed, if excavation is possible, assessment of the geometric and mechanical characteristics of the jet grouted elements should be made by visual inspection of the exposed jet grouted elements and by laboratory tests on samples recovered by coring or excavation.

9.2.3 Where preliminary tests are performed, if the jet grouted elements cannot be exposed, the assessment of the results (mainly the size of the elements) should be made by coring or by direct measurement prior to setting, or by indirect tests.

9.2.4 If coring or above indirect tests are applied to check the "as built" geometry of the elements of the main works, and visual inspection of preliminary elements is possible, the same methods should be applied also to the preliminary elements and their results should be compared with visual inspection, to check the reliability of the methods.

9.2.5 Indirect tests and laboratory tests performed on samples recovered by coring should be selected with care, having regard to the practical limitations to their reliability.

9.2.6 Annex C lists some indirect tests that can be applied.

9.3 Supervision and process testing

9.3.1 Pressure gauges and other meters to be used in the measurements of the jetting parameters shall be calibrated before commencement of the works.

9.3.2 The pressure of the fluids is commonly measured as pump pressure. In cases where long lines or very deep treatment is necessary the head losses should be taken into account.

9.3.3 For long duration contracts periodic calibration of the instruments can be required for quality control.

9.3.4 The inclination of the jet grouted elements shall be assessed by measuring the inclination of the jet grouting string at the surface before and during drilling, if not otherwise stated by the design.

9.3.5 The spoil return flow and features shall be visually observed and the description recorded.

9.3.6 The density of the spoil return should be periodically measured and recorded. The reasons for any unexpected results should be explored.

9.3.7 Representative samples of the spoil return should be taken and submitted to compression tests.

9.3.8 The following tests on the grout mix should be performed:

  • — preliminary tests:
  • — density;
  • — bleed (3 hours on 1 000 cm 3, 60 mm diameter, cylinder);
  • — marsh viscosity;
  • — setting time;
  • — unconfined compression tests on cylindrical samples (height/diameter ratio 2,0) at 3, 7, 28 days; 56 days if slowly hardening mixes are used;
  • — tests during the work:
  • — density (minimum twice a shift); Marsh viscosity (daily);
  • — bleeding (daily).

EN 12716:2001 Execution of special geotechnical works — Jet grouting