4 Specific needs

4.1 The following information shall be determined prior to design or execution activities:

  • — detailed description of the ground profile and its geotechnical properties within the intended extent of treatment;

and, as appropriate:

  • — hydrogeological conditions;
  • — boundary conditions (adjacent structures, buried structures and services, overhead power lines and other working restrictions, access);
  • — environmental requirements; in particular disposal of spoil return;
  • — acceptable deformation of the structures to be underpinned or of adjacent structures.

4.2 Design assumptions according to ENV 1997-1-1:1994 - clause 2 shall be verified, and modified if necessary, according to information obtained during the execution phase.

4.3 Due to the nature of jet grouting works, the client, the main contractor, a specialist contractor or a consulting engineer, may perform all or parts of the design.

4.4 The allocation of design, execution and supervision activities and responsibilities of all the parties involved shall be legibly specified in the contract documents.

4.5 Design and execution should include, as appropriate, the activities listed in table 1. The order shown does not necessarily represent a time sequence.

Table 1 — Recommended list of activities in the design and execution of jet grouting
Activity
1 Provision of site investigation data for execution of jet grouting works.
2 Decision to use jet grouting, preliminary trials and testing if required; provision of a specification.
3 Acquisition of all legal authorization necessary for the execution from authorities and third parties.
4 Overall design of jet grouted structure and definition of the geotechnical category.
5 Consideration of the relevant temporary phases of execution.
6 Assessment of the site investigation data with respect to design assumptions.
7 Assessment of the construction feasibility of the design.
8 Execution of trials if required and of any relevant tests.
9 Evaluation of the results of the preliminary trials and tests.
10 Selection of jet grouting system.
11 Assessment of the jet grouting system and definition of the working procedures.
12 Definition of the dimensions, location and orientation of jet grouted elements.
13 Instructions regarding the working sequence if required.
14 Definition of the working sequence.
15 Instruction to all parties involved of key items in the design criteria to which special attention should be directed.
16 Specification for monitoring the effects of jet grouting works on adjacent structures (type and accuracy of instruments, frequency of measurement) and for interpreting the results.
17 Definition of tolerable limits of the effects of jet grouting works on adjacent structures.
18 Execution of the jet grouting works, including monitoring of the jet grouting parameters.
19 Supervision of the works, including the definition of the quality requirements.
20 Monitoring the effects of jet grouting works on adjacent structures and presenting the results.
21 Control of the quality of works.
 

5 Geotechnical investigation

5.1 Jet grouting is a ground treatment method and shall be designed on the basis of the geotechnical characteristics of the ground; therefore an accurate geotechnical investigation is essential.

5.2 All geotechnical investigation shall be undertaken in accordance with the requirements and recommendations of ENV 1997-1:1994, in particular with reference to the geotechnical categories in points 2.1, 3.2, and 3.3.

5.3 Where possible geotechnical investigation should be extended to the site boundaries so that the soil profile can be interpolated between the investigated axes rather than extrapolated outside them.

5.4 Special consideration shall be given to the following geotechnical conditions:

  • — firm or stiff cohesive layers or lenses;
  • — high organic content;
  • — swelling soils;
  • — highly sensitive or quick clays;
  • — cemented layers or lenses;
  • — position of water table(s);
  • — presence of artesian or confined aquifer conditions;
  • — high hydraulic gradients;
  • — aggressive soil or water;
  • — density of granular layers;
  • — cobbles and/or boulders;
  • — large voids or high permeability;
  • — chemical wastes or deposits.

5.5 In addition to the lithology and structure of the ground in accordance with ENV 1997-1:1994, the following features and parameters shall also be determined, through laboratory and/or in situ tests, as applicable:

  • — grain size distribution, moisture content, Atterberg limits;
  • — density, by direct or indirect measurement;
  • — shear strength, by direct or indirect measurement.

5.6 In situ mechanical testing of the soil should be used to identify variations of density.

6 Materials

6.1 Unless otherwise specified, the properties of the materials shall comply with European standards.

6.2 Mixes composed of water and cement are usually adopted.

6.3 Hydraulic binders other than cement can be used.

6.4 In water/cement mixes the water/cement ratio by weight should range between 0,5 and 1,5.

6.5 Water reducing, stabilizing, plasticising, waterproofing or antiwashing admixtures can be added to the water/cement mix.

6.6 Other materials, such as bentonite, filler, fly-ash, can also be added to the mix.

6.7 When bentonite is to be used in the mix, a water/bentonite suspension should be prepared before adding cement.

6.8 Any recognized potable water is normally acceptable for the preparation of jet grouting mixes.

6.9 Water from sources other than recognized potable water suppliers shall be analysed in order to ensure that it will have no adverse effect on the setting, hardening or durability of the mix and, where applicable, will not promote corrosion of the reinforcement.

6.10 If the cement does not comply with the standard ENV 197-1:1992, appropriate tests shall be performed in order to ensure that the setting time, hardening, strength and durability requirements, as stated by design specifications, are met.

6.11 Care should be taken to ensure that no large particles are present in the jetting materials, as they can block the nozzles.

6.12 Acceptance criteria and water testing methods as required by subclause 6.9. shall conform to prEN 1008:1997.

6.13 Where reinforcement is obtained by steel bars, the material shall comply with ENV 1992-1-1:1991 - clause 3 and 6 as appropriate.

6.14 Where material other than steel bars is used for reinforcement, it shall comply with national standards or with design technical specifications.

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