In situ Soil Injection Simulator – ISIS

ISIS is a pre-construction, laboratory test for determining the injectability of various grouts to a particular or variety of soil horizons. Ground conditions are simulated and grout is injected. ISIS is set up such that the ‘grouted block’ can be removed from the test cell for direct observation and analysis.

ISIS is a useful tool for marketing of various grout products (regular and microfine cements and solution grouts), as well as pre-construction testing for development of performance criteria and design criteria.

How ISIS is Utilized

ISIS can be utilized for site specific solutions or as a marketing tool for various grout products such as microfine cements, solutions grouts and additives.

Project Testing – ISIS is a very usefull tool for determining design and performance criteria for specific projects. ISIS allows for the simulation of site specific soil conditions which then permits testing to determine the injectability of the soil. Proper grout formulations and methodology can be determined before production work begins on site. Post grouting soil properties can be determined and thus a predicatble end product known. The following properties and characteristics can be reproduced or determined:

Soil Properties (duplication of site specific soil properties)

  • Grain size (sieve curve)
  • Moisture content
  • Density

Grout Mixes Design

  • Grout type (regular or microfine cement or solution grouts)
  • Oprimal grout mix design (optimization of Amenability)
  • Sequence (procedure) of grouting
  • Required additives for desired end product

Treated Soil Chraracterisitics

  • Residual permeability
  • Treat soil strength
  • Lateral treatment (hole spacing)

Product Testing – ISIS can be used to test new products or optimize and product for a particular application. ISIS is particularly useful for testing of microfine cements and solution grouts to determined the limits of injectability in various ground conditions. Additives can also be tested to determine their use in grout mix designs. ISIS can be used to test various grout mixes in any variety of soil conditions as follows:

Injectability (for additives and grout products)

  • lateral spread (travel distance from injection point),
  • pore size permeated (injectability limits)
  • treated soil strengths
  • residual permeability

Grout mixes can be optimized in our lab and tested with ISIS. Four tests can be performed in an inidividual test cell. Refer to Grout Design and Analysis for the capabilities of our lab testing.

How ISIS Works

ISIS allows for the re-construction of site-specific soil conditions. Up to 4 soil layers can be constructed within one test cell. Soil characteristics such as; sieve analysis, water content and density are used to recreate the soil conditions. Three different sands (course, medium and fine) are stored on site for mixing to reproduce the desired soil conditions. A specified silt content can also be added. An impervious layer is used to separate the soil layers . Grout is injected via a multiple phase sleeve pipe (MPSP) installed in the center of the test cell. A double packer is used to isolate each sleeve and thus perform 4 separate tests. Each grouting phase is monitored using CAGES , a system of monitoring pressures and flows and determining amenability. At the completion of injection, the soil sample is removed from the test cell for observation and analysis.

Since 4 separate layers are contained in one test cell, a variety of soil conditions and/or grout mixes can be tested.

Purpose

ISIS has been developed in order to evaluate the following:

  • The injectability of different soil horizons with a pre-determined solution grout or microfine suspension grout.
  • To determine the lower limits of injectability (lowest permeability value, finest soils, and greatest tolerable silt percentage) with a particular solution or suspension grout, with which adequate permeation is still possible.
  • To optimize grout formulations (either solution or suspension grouts), to ensure desirable injectability into the given soil horizon is obtained.
  • To evaluate if a particular soil with a given density and gradation (which is reproduced in the ISIS test chamber) is injectable with either regular or microfine cement based grout or with solution grout.

Injectability tests currently being conducted in North America on a lab scale are usually fundamentally flawed. Current tests typically are conducted as follows; cylinders with a diameter of 100 mm are filled with soil and grouted from the top down. This method does not take into account the impact of boundary conditions on the ultimate injectability. Cambefort, mathematically proved the important role of the thickness of the soil layers on their injectability. For this reason, it is necessary to determine injectability, using layers which are (sufficiently thick – minimum 250 mm) and extending laterally (from the injection point) at least 250 mm.

Through ISIS, ECO has developed a system whereby a series of 300 mm thick soil layers can be placed in our test chamber (1200 mm diameter). The compaction of the soil and any overburden pressures will then be simulated identically to those on site conditions.

Soil grouting takes place in various passes in each zone (defined by the sleeve pipe spacing). With past testing procedures there was no way to simulate how these zones were behaving after each pass. ISIS allows us to simulate the exact grouting program, under the exact site conditions, thus producing an accurate interpretation of what will occur in the field.

With ISIS we can now find out which formulations are best suited for optimum permeation, for lowest residual horizontal permeability and for optimum strength in the treated soils, at the lowest possible cost.

Development of ISIS

ECO developed ISIS in-house as an advanced laboratory test for determining the injectability of grout formulations to various soil conditions. The grouting industry was in need of a reliable method to better predict hole spacing, lateral treatment, residual permeability, in situ strength.

Injectability tests currently being conducted in North America on a lab scale are usually fundamentally flawed. Current tests typically are conducted as follows; cylinders with a diameter of 100 mm are filled with soil and grouted from the top down. This method does not take into account the impact of boundary conditions on the ultimate injectability. Cambefort, mathematically proved the important role of the thickness of the soil layers on their injectability. For this reason, it is necessary to determine injectability, using layers which are (sufficiently thick – minimum 250 mm) and extending laterally (from the injection point) at least 250 mm.

For too long, grouting practitioners have been using unstable or marginally stable microfine cement based grouts, resulting in high residual horizontal permeability, and in some cases, limited grout spread. Others have tried to make a case that low water/cement ratios would result in a better grout formulation, thereby ignoring the fact that a more cohesive Binghamian fluid can only flow as far as determined by Lombardi’s equation. In most cases, the influence of particle pick-up has been ignored i.e. the grout dislodges fine (silt) particles from the soil matrix which in turn becomes part of the suspension grout.