9 Supervision of execution and monitoring (p. II)
Table 4 — Controls for precast concrete diaphragm walls
| Construction phase or item | Control | Comments |
| Setting-out | – Position of wall | – From lay-out drawings and fixed setting out points |
| – Position and level of guide-walls | – Shall be checked before they are concreted and again after removal of the formwork | |
| – Position of excavation units | – Shall be marked on the guide-walls, and when necessary, the amount of overlap shall be indicated | |
| – Position of elements | – Shall be marked on the guide-walls | |
| Water | – Suitability for use | – Usually not required for potable water |
| Bentonite, cement or other binders, additions | -Source of supply | – Delivery documents shall be checked for each load |
| Self-hardening slurry | – Density, Marsh value | Items to be checked prior to the commencement of work |
| – Setting time, bleeding | – Test methods to be specified | |
| – Compressive strength | – Unconfined compression test (at 28 days) | |
| – Permeability | – If required. Usually performed with tap water. In special cases, groundwater may need to be used | |
| Delivery of precast elements | – Identification of elements – Geometry and aspect of elements and joints |
Items to be checked for each element with respect to the working drawings |
| Excavation | – Position of tool | – Visual observation |
| – Verticality and continuity between excavation units or excavation sections, as appropriate | – Shall be checked for each excavation unit or excavation section, during and at the end of excavationa | |
| – Ground profile | ||
| – Depth of excavation | ||
| – Self-hardening slurry level | – Visual observation | |
| – Position of excavation sections, in the case of a continuous excavation process | – The position of the end of the excavation shall be checked after completion of each excavation section | |
| Self-hardening slurry to be placed in the excavation | – Density, Marsh value, bleeding | – To be checked at least once per shift |
| Self-hardening slurry taken from excavation | – Setting time | – To be checked every day |
| – Compressive strength | – Unconfined compression test (at 28 days). To be checked once per week | |
| – Ability of hardened slurry (or bottom mortar if any) to support precast element | – To be checked at the beginning of the work and thereafter, once per week | |
| Installation of precast elements | – Depth of excavation section | – To be checked before insertion, at each element position |
| – Identification of element | ||
| – Position of water-stops (if any) | Items to be checked for each element | |
| – Position of suspension devices | ||
| – Orientation with respect to the exposed face of the wall | ||
| – Position and verticality of element during lowering | ||
| – Position, level and verticality of element after installation | ||
| – Position of the elements after setting of the slurry | ||
| Removal of suspension devices | – Time of removal in relation to the strength of the slurry (or bottom mortar if any) | – To be checked for each element |
| a Verticality and continuity of the excavation shall be controlled in order to remain within the required tolerances. The monitoring frequency shall be increased for cases presenting high risk, such as where boulders or obstructions are present in the ground. These controls shall normally be by visual observation or simple measurements (e.g. position of grab cables). | ||
Table 5 — Controls for reinforced slurry walls
| Construction phase or item | Control | Comments |
| Setting-out | – Position of wall | – From lay-out drawings and fixed setting out points |
| – Position and level of guide-walls (if any) | – Shall be checked before they are concreted and again after removal of the formwork | |
| – Position of excavation units | – Shall be marked on the guide-walls or on the ground, and when necessary the amount of overlap shall be indicated | |
| – Position of reinforcing elements | – Shall be marked on the guide-walls or on the ground | |
| Water | – Suitability for use | – Usually not required for potable water |
| Bentonite, cement or other binders, additions | – Source of supply | – Delivery documents shall be checked for each load |
| Self-hardening slurry | – Density, Marsh value | Items to be checked prior to the commencement of work |
| – Setting time, bleeding | – Test methods to be specified | |
| – Compressive strength | – Unconfined compression test (at 28 days) | |
| – Permeability | – If required. Usually performed with tap water. In special cases, groundwater may need to be used | |
| Delivery of reinforcement | – Number, dimensions and location of beams or bars – Welds and couplings |
Items to be checked with respect to the working drawings |
| Excavation | – Position of tool, overlap | – Visual observation |
| – Verticality and continuity between excavation units or excavation sections, as appropriate | – Shall be checked for each excavation unit or excavation section, during and at the end of excavation a | |
| – Ground profile | ||
| – Depth of excavation | ||
| – Self-hardening slurry level | – Visual observation | |
| – Position of excavation sections, in the case of a continuous excavation process | – The position of the end of the excavation shall be checked after completion of each excavation section | |
| Self-hardening slurry to be placed in the excavation | – Density, Marsh value, bleeding | – To be checked at least once per shift |
| Self-hardening slurry taken from excavation | – Setting time | – To be checked every day |
| – Compressive strength | – Unconfined compression test (at 28 days) , unless otherwise specified. Tests shall be performed on 2 samples taken at different depths. Frequency as specified | |
| Installation of reinforcement | – Depth of excavation section | – At specified spacing along the wall, before insertion |
| – Rigidity of reinforcement | – To be checked during lifting of the first reinforcement unit of each type | |
| – Reference number | ||
| – Orientation with respect to the exposed face of the wall | ||
| – Position and verticality during lowering | ||
| – Connection between vertical elements during lowering | – Especially the length of laps | |
| – Final level and position | ||
| Topping up | – Slurry level | – Add slurry if necessary |
| a Verticality and continuity of excavation shall be controlled in order to remain within the required tolerances. The monitoring frequency shall be increased for cases presenting high risk, such as where boulders or obstructions are present in the ground. These controls shall normally be by visual observation or simple measurements (e.g. position of grab cables). Special measures (e.g. inclinometers) to determine the excavated profile may be necessary in some cases, e.g. in deep panels. | ||
Table 6 — Controls for slurry cut-off walls
| Construction phase or item | Control | Comments | |
| Setting-out | – Position of wall | – From lay-out drawings and fixed setting out points | |
| – Position and level of guide-wall (if any) | – Shall be checked before they are concreted and again after removal of the formwork | ||
| – Position of excavation units | – Shall be marked on the guide-walls or on the ground, and when necessary, the amount of overlap shall be indicated | ||
| Water | – Suitability for use | – Usually not required for potable water | |
| Bentonite, cement or other binders, additions | – Source of supply | – Delivery documents shall be checked for each load | |
| Self-hardening slurry | – Density, Marsh value | Items to be checked prior to the commencement of work | |
| – Setting time | – If required (deep walls, membranes, etc). Test method to be specified | ||
| – Bleeding | – Test method to be specified | ||
| – Gel strength | – When deemed to be necessary | ||
| – Compressive strength | – Unconfined compression test (at 28 days) , unless otherwise specified | ||
| – Deformation modulus | – If specified | ||
| – Permeability | – Usually performed with tap water on 28 day samples. In special cases, groundwater may need to be used. Periods greater than 28 days can be used depending on project requirements | ||
| Delivery of possible elements to be inserted (sheetpiles, membranes, etc) | – Items to be checked depend on type of element to be inserted | Items to be checked for each element with respect to the working drawings | |
| Excavation | – Position of tool, and when necessary amount of overlap | – Visual observation | |
| – Verticality and continuity between excavation units or excavation sections, as appropriate | – Shall be checked for each excavation unit or excavation section, during and at the end of excavation a | ||
| – Ground profile | |||
| – Depth of excavation | |||
| – Self-hardening slurry level | – Visual observation | ||
| – Position of excavation sections, in the case of a continuous excavation process | – The position of the end of the excavation shall be checked after completion of each excavation section | ||
| Self-hardening slurry to be placed in the excavation | – Density, Marsh value, bleeding | – To be checked at least once per shift | |
| Self-hardening slurry taken from excavation | – Setting time | – To be checked every day, if required (deep walls, membranes, etc.) | |
| – Compressive strength | – Unconfined compression test at 28 days, unless otherwise specified | Frequency as specified. Tests shall be performed on 2 samples taken at different depths | |
| – Deformation modulus | – If specified | ||
| – Permeability | – If specified. Usually at an age of 28 days | ||
| Inserting an element (if any) | – Depth of excavation section | – At specified spacing along the wall, before insertion | |
| – Interlocking of elements | – At every lock, when applicable | ||
| Topping up | – Slurry level | – Add slurry if necessary | |
| a Verticality and continuity of excavation shall be controlled in order to remain within the required tolerances. The monitoring frequency shall be increased for cases presenting high risk, such as where boulders or obstructions are present in the ground. These controls shall normally be by visual observation or simple measurements (e.g. position of grab cables). Special measures (e.g. inclinometers) to determine the excavated profile may be necessary in some cases, e.g. in deep panels. | |||
