9 Supervision, testing and monitoring

9.1 Supervision and monitoring

9.1.1 General A suitable quality control procedure shall be established for supervision and monitoring. The supervision of the ground treatment shall be carried out by suitably qualified and experienced persons and in accordance with Clause 4 of EN 1997-1:2004. A plan for the supervision should be available at the ground treatment site. As a minimum, the following shall be noted:

  • written procedures, which include a list of critical control parameters;
  • site and ground conditions, and significant departures from the design basis;
  • any obstructions in the ground which hinder or prevent penetration of the ground by the vibrating tool. The effect on the design of any changes to specified treatment procedures where unforeseen conditions are encountered or new information about soil conditions becomes available, shall be evaluated and action agreed prior to the change being made. Critical control parameters shall be monitored during the treatment process, and recorded. Continuous recording shall be used. Execution parameters listed in Clause 10 shall be monitored. Where adverse effects on the surrounding ground have been identified, suitable monitoring shall be included in the written procedures.

9.1.2 Deep vibratory compaction

In addition to the items listed in 9.1.1, the following should be monitored as they provide a means of assessing the treatment and information which can be used in controlling the treatment:

  • where fill is imported, the quantity of imported fill, its origin, type and grading;
  • where no fill is imported, the settlement of the ground surface.

9.1.3 Vibrated stone columns Significant variations in consumption of granular material used in forming columns of the same length shall be noted and its effects on the design considered. Any changes in supply or specification of the materials shall be noted and its effects on the design considered.

9.2 Testing

9.2.1 General The primary purpose of testing is to assess the performance of the treatment. With stone columns, some additional testing is done for quality control purposes. The choice of test method should be influenced by the objective of ground treatment. In some situations, the time that has elapsed between treatment and testing will have a significant effect on the test result. The test method shall be specified using, wherever possible, international reference test procedures such as those listed in prEN 1997-2. The parameters to be monitored, the test locations, the frequency of testing and criteria for acceptance shall be defined prior to execution. Testing shall be appropriate for the amount of treatment, variability of ground conditions, type of foundation, depth of influence of foundation loading and any other relevant factors. The number and type of tests and their locations and depth shall be recorded. Signed copies of these records and the test results shall be submitted as required by the contract.

9.2.2 Deep vibratory compaction In situ tests should be used for performance testing where changes in ground properties can be measured and directly related to criteria set out in the contract documents or to рге-treatment data obtained using the same technique. One or more of the following in situ tests may be carried out:

  • cone penetration tests (CPT and CPTU) carried out to provide a continuous record of penetration resistance, friction ratio and, for CPTU, induced pore pressure;
  • dilatometer tests (DMT) carried out to determine deformation moduli;
  • dynamic probing (DP) carried out to provide a record of the penetration resistance;
  • pressuremeter tests (PMT) carried out to determine deformation moduli and/or limit pressures;
  • standard penetration tests (SPT) carried out to determine the penetration resistance.

The parameters derived from these in situ tests can be empirically correlated with the parameters which control mass behaviour, but a comparison of in situ tests carried out before and after treatment will not necessarily reflect the actual improvement in the mass of treated ground. When carried out at a suitable scale and over an appropriate period, loading tests can give a direct measurement of the parameters that control mass behaviour as described in 9.2.3. Other types of testing may be appropriate for particular applications and ground conditions, including geophysical testing, such as seismic wave velocity measurements, sampling and laboratory testing, and borehole permeability testing.

9.2.3 Vibrated stone columns Where vibrated stone columns are installed in granular soils, the tests listed in 9.2.2 may be applicable. The parameters to be monitored, the test locations, the frequency of testing and criteria for acceptance shall be defined prior to execution. Large scale load tests include large plate load tests and zone tests:

  • large plate load tests for performance testing should be carried out by loading a rigid plate or cast in situ concrete pad large enough to span one or more columns and the intervening ground;
  • zone tests should be carried out by loading a large area of treated ground, usually by constructing and loading a full size foundation or placing earth fill to simulate widespread loads.

Location, parameters to be measured, loading procedure, load increments, duration of the test, and load/reload cycles should be specified prior to testing. Individual column plate load tests should be carried out using a plate placed concentrically on individual columns, loaded in increments with the settlement of the plate measured against a stable reference beam.

9.2.4 Materials The hardness of the granular material used to form stone columns should be checked. Where required, tests should be carried out in accordance with procedures for tests of mechanical and physical properties of aggregates given in EN 1097. Where required, the particle size distribution of the granular material should be determined in accordance with prEN 1997-2.

10 Records

10.1 Records in connection with the execution of the ground treatment

Daily records of the treatment process shall be kept and shall be available at the ground treatment site. The records shall show:

  • reference number and location of treatment point;
  • date and time of work at each treatment point;
  • weather conditions;
  • method of treatment, reference type of equipment and personnel;
  • depth of penetration at each location;
  • time required to reach maximum depth and details of times and depths during withdrawal;
  • vibrator power consumption during penetration and compaction of granular material or soil for depth vibrators;
  • obstructions and delays;
  • any unforeseen conditions encountered;
  • presence of heave or settlement of ground surface;
  • where stone columns are installed, the quantity used in each column;
  • with wet or bottom-feed processes, any occasions when the depth vibrator has had to be removed from the ground during column construction.

10.2 Records at completion of the ground treatment

In the final site records, the following shall be included:

  • the as-executed position and depth of each treatment point noting any deviation outside specified tolerances;
  • particular directives associated with design and execution which are relevant to subsequent use of the treated ground;
  • where stone columns are installed, the source, type and quality of granular material.

11 Special requirements

11.1 General

Only those aspects of site safety and protection of the environment which are specific to ground treatment by deep vibration are considered. All relevant European and national standards, specifications and statutory requirements regarding safety and the environment shall be observed.

11.2 Safety

11.2.1 The ground treatment shall be carried out in a safe manner, including conformance with EN 791 on drilling rig safety and/or with EN 996 on piling equipment safety.

11.2.2 The treatment process involves personnel operating alongside heavy equipment with items suspended from the jib of a crane; safe working practices shall be observed.

11.2.3 Where the treatment process involves a risk of liquefaction, special attention shall be given to the stability of base machines and the overall stability of the site, particularly when working in close proximity to slopes or excavations.

11.3 Environmental protection

Nuisance and/or environmental damage can be caused by noise, dust, vibration and the disposal of effluent. Where required, measures shall be taken in order to limit or avoid such adverse effects. Where water is injected into the ground during treatment, all requirements of the statutory authorities shall be clearly defined.

11.4 Impact on adjacent structures

11.4.1 Where buildings, structures and services are located within or close to the boundary of a proposed area of ground treatment, consideration shall be given to the effects of the treatment upon them arising from vibration and ground movement.

11.4.2 The condition of adjacent structures and installations should be observed and documented prior to the execution of ground treatment and monitored during ground treatment. In appropriate cases, expert advice should be sought prior to commencement of the treatment.

11.4.3 Where required, vibration monitoring shall be carried out during the treatment process with prior agreement of threshold levels.

EN 14731:2005 Execution of special geotechnical works - Ground treatment by deep vibration