7 Design considerations
7.1.1 The basic standard for the design of grout injections is:
- ENV 1997-1:1994, EUROCODE 7: Geotechnical design – Part 1: General rules.
7.1.2 This present standard supplements the above document and establishes additional requirements and recommendations for the planning and implementation of geotechnical grouting applications.
7.2 Design basis and objectives
7.2.1 A flexible approach should be adopted to the design and planning of a grouting application in order to adapt the works to unforeseen ground conditions or variations in the behaviour of the host materials as the work progresses.
7.2.2 The principal objectives of geotechnical grouting are:
- the modification of the hydraulic/hydrogeological characteristics the ground;
- the modification of the mechanical properties of the ground;
- the filling of natural cavities, mine workings, voids adjacent to structures;
- inducing displacement to compensate for ground loss or to stabilize and lift footings, slabs and pavements.
7.2.3 In order to formulate a grouting design, the following information shall be made available:
- a definition of the grouting objectives and the control criteria;
- adequate ground information, in particular geological, geotechnical and hydrogeological data (including water chemistry) relevant to grouting (see clause 5);
- limitations imposed by environmental considerations, the influence of or on adjoining structures (buildings and foundations) or any other parameters which could affect the choice of grout mix and placement technique;
- references to other grouting projects executed in the same area or under comparable circumstances.
7.2.4 Based on the site investigation, the grouting trials and the design, the following aspects shall be considered and addressed by the working documents:
- the shape and volume of the ground to be treated;
- the measurable properties to be achieved for the life of the project;
- the drilling method and pattern;
- the grouting techniques and methods to be applied;
- the spacing of injection points;
- the sequencing of the injections with respect to time, grout composition and injection point;
- permissible grouting limits (injection pressure, flowrate and quantity of grout to be injected);
- the grout mix compositions;
- the required tests and field controls to be adopted before, during and after grouting;
- the instrumentation required for monitoring and data logging.
7.2.5 The following aspects should be considered during grouting:
- the reliability and completeness of the ground information available;
- the performance required of the grout;
- the presence of existing structures and their condition;
- changes induced in the in situ state of stress and pore pressures as a result of the grouting work, the existing groundwater conditions as well as expected post construction conditions;
- the toxicity of the grouting products;
- the working environment in which the grouting materials have to be stored, mixed and injected;
- the availability and reliable supply of grouting materials;
- environmental and safety restrictions.