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JET GROUT

GENERAL

The purpose of this typical method statement is to provide general guidance on jet grouting works. Project specific method statement shall be submitted prior to commencement of the Works based on project specific requirements.
If the prevailing site conditions preclude practical application of the whole or parts of the procedure explained below, alternative techniques may be applied. All alternative procedures will be in conformity with the generally accepted jet grout practice and the Engineer’s approval will be sought prior to any variation in method of construction.
A jet grout Column with various diameters can be performed according to this Method Statement.

  1. REFERENCES
  1. Related Drawings
  1. SCOPE OF WORK
  1. Preparation of grout
  2. Boring the holes
  3. Performing column

 

4.  PRE-CONSTRUCTION ACTIONS

  1. Working hours shall not be limited for jet grouting
  2. The necessary lighting shall be provided for the night shift with lighting fixtures.

The work site shall be leveled and compacted to form an adequate platform suitable for heavy drilling rigs and other auxiliary equipment working on it. Surveyors will stake out the center location of each jet grout using the reference points on site. Stakes shall be numbered in accordance with the numbering system on the drawings.
Before commencement of the jet grouting works, grouting plants consisting of cement silos, jet grouting pumps and mixers will be prepared. Location of the plant shall be within a reasonable distance from the jet grouting location.

 

5. RESPONSIBILITIES

  1. Engineer

Responsible for the activities carrying out as described in contract description, specification and drawings

  1. Site Foreman,

Responsible for the execution of the jet grouting activities

6. DESCRIPTION OF WORK

The piling program shall be carried out on the following work flow diagram.

6.2 WORKING PLATFORM

A firm working level platform is to be provided and maintained the surface is to be suitable for the safe operation of our jet grout drilling equipment. Prior to our commencement on site, any sub-surface obstruction likely to impede our works shall be broken out and removed from the pile positions. Any additional services are to be made known to our site foreman, indicated on a drawing and marked out clearly on site.
6.3 PLANT & EQUIPMENT
Major items of plant and equipment are detailed below.

  1. Hydraulic Drilling Rig – crawler mounted rig of brand Casagrande type C6 or similar.
  2. 40 ton capacity cement storage or similar
  3. Ready made grout plant of brand Tecniwell type TW400 or similar
  4. High Pressure Pump of brand Tecniwell type TWM20 or similar.
  5. Container Stores– lockable steel units approximately 2.4m*6m*2.5m and/or 3m*7m*2.5m or similar. The number of items will be as needed.

6.4 MATERIAL
All material shall comply with relevant technical specifications and the standards as denoted there.

6.4.1 CEMENT
Suitable type of cement is to be used. Test results shall be submitted to Main Contractor prior the commencement of the works for approval.

6.4.2 WATER
Fresh water without any kind of contamination is to be used.

6.5 PERFORMING JET GROUT COLUMN
Jet grouting is a construction process using a high kinetic energy jet of fluid to break up and loosen the ground and mixing it with a thin slurry. It is not truly grouting but rather a hydrodynamic mix-in-place technique producing a soil-cement material. The basic construction procedure is to set up on location, drill down to designated tip level  using a hydraulic drilling rig, commence jet grouting through the nozzles at the end of the drilling rod and just above the drilling bit, rotate and withdraw the drilling/grouting rod and stop grouting when the specified depth is reached.
The concept first appeared in the late fifties in the United Kingdom. Single, double and triple jets carry the necessary hydrodynamic energy to break up and mix the soil with the slurry. It is suitable for mass treatment, linear treatment and inclusions, in soils of good to poor groutability.
The equipment is composed of a stationary part (cement storage, ready made grout plant, high pressure pump) joined by a flexible high pressure to the ground boring machine that moves on its tracks to each jet grout column center point. The head of the boring rods is equipped with injection nozzles specially chosen according to the ground and the expected characteristics of the treatment.

Jet grouting makes use of three physical processes:
-the very high speed jet loosens the soil
-the jetting fluid washes some of the soil to the surface
-the slurry adds a binder to the soil mix

The sequence of work is usually as follows:

-A small (100-200mm dia.) hole is drilled to the required depth,
-A high pressure (several dozen Mpa) fluid is pumped through one or more small (1-10mm) nozzles on a monitor at the foot of a 89 mm dia. Drill string,
-The drill string is slowly raised and rotated to form a column of soil cement.

During jetting, material in excess of the soil cement mix must rise freely to the hole collar (to prevent the excess material fracturing and disturbing the surrounding ground). It is removed from site as it emerges.

The result (diameter, composition and strength of the columns) is dependent on drill string rotation and raising speeds, jet pressure and flow, grout mix; soil type, grain size distribution, composition and compactness; and jet configuration (single, double or triple jet set-up).

The parameters which will be followed are mainly :
•     Grouting pressure
•     Number and size of Nozzle
•     Rod rotation speed (RPM)
•     Rod lifting time (cm/min)
In order to determine project value several number of trial columns are to be performed with a variety of paremeters (drill string rotation and raising speeds, jet pressure and flow, grout mix)

7. QUALITY CONTROL

To assure a high standard of jet grout construction a complete quality control scheme should be applied.
In the first place, in all stages of the production the details shall be neatly recorded in the report forms.
Secondly, routine inspection shall be applied on the grout and cement.
At the end, selected completed jet grout columns may be tested for manufacturing defects and performance.
As a result one or several methods may be used for pile testing:

  1. Pile integrity test by sonic echo method
  2. Column load test

7.1 PRODUCTION RECORDS

The production record forms to be filled during execution of the works are listed below. .

    1. Jet grout column construction report

This report will include the followings:
-      Jet grout number, location and installation date
-      Column no
-      Column diameter
-      Nozzle diameter
-      Number of nozzle
-      Jet grout length
-      Drilling length
-      Grout pressure
-      Rotation
-      W/C ratio

7.2 TRIAL COLUMN

Prior to our commencing of jet grout column several jet columns are to be performed with a variety of parameters (drill string rotation and raising speeds, jet pressure and flow, grout mix). After being excavated of all trial columns, the parameters of jet grout columns which are corresponding project data is to be used to as ultimate jet grout column parameters.
  Bored Pile Anchor Diaphragm Wall Jet Grout Load Tests