Backfilling Technology
Plant solutions for tunneling and underground structures.
The tunnel construction technique has been increasingly evolving over the years, with new methodologies, especially when it is necessary to operate in loose soils with or without groundwater.
The excavation methods performed with TBM (Tunnel Boring Machine) require a special attention to the completion of several operative phases and in particular it is very important to take care of the technique of filling of the annular space between the inner concrete lining and the natural soil.
This technique is defined “Backfilling” and for its application is usually required the preparation of a “Bi-component” MIXTURE.
A common “bi-component” MIXTURE is composed with:
Water
Bentonite
Cement
Retarder additive
Accelerator additive
A. Cement and bentonite storage of custom dimensions
B. High capacity mixing group with water and admixtures integrated dosing systems
C. Mixture agitated storage with transferring pumping group
Main Parameters for plants design
Mixtures design and physical features.
Geometric and topographical characteristics of the longitudinal profile of the tunnel.
Features of the pipes for the mixtures transfer.
Geometric features of the excavation and of the lining.
Advancement speed of the TBM and expected times for the various operations.
Logistic conditions outside the tunnels, for fixed installations.
Logistic conditions inside the TBM.
Monitoring systems for equipment and data transferring.
Duration of the works and evaluation of the spare parts warehouse and reserve equipment.
Operative main steps
1.
MIXTURE PREPARATION
High productivity automatic mixing set
2.
MIXTURE STORAGE
Big size agitators
3.
MIXTURE TRANSFERRING
Transferring pump with high flow rates and working pressures
4.
MIXTURE INJECTION
Small and flexible grouting injectors
Mixing Unit
MIXTURE PREPARATION
The first step, usually performed outside the tunnel, consists in the preparation of the fluid mixture with:
water + bentonite + cement + retarder.
For its preparation, it is required to have:
- High capacity mixing plant (20÷50 mc/hr);
- Silos for cement-bentonite powder storage;
- Crew conveyors of appropriate capacity for cement and bentonite powders feeding to the mixing tank.
Backfilling technology Mixing Unit
Containerized or on basic skid.
M20
M30
Big Tank Agitators
MIXTURE STORAGE
Once packaged, the primary mixture must be stored and accumulated inside large agitators which, through shafts with mixing blades and recirculation pumps, keep the mixture in motion, ready to be transferred to the TBM through the transfer pumps.
This operation is essential to avoid separation and bleeding in the mixes and also to always have an adequate volume of mix ready according to the needs of the TBM.
A15000
Transferring pumps
MIXTURE TRANSFERRING
The transfer of the bicomponent mixtures from the storage buffers to the TBM takes place through pumps with suitable flow and pressure characteristics.
The injection rates are generally based on the geometry of the excavation and the lining segments, as well as of the advancement speed of the TBM.
The working pressures, to be evaluated according to the required flow rates, are generally sized in consideration of the type of pipe, the pipe diameter and the linear and altimetric development of the TBM excavation path.
According to the project features, a range of pumps is available, always considering the redundancy with one or more stand-by pumps to be used in the event of breakdowns,in order to avoid by any means slowdowns or interruptions of the TBM.
Clivio CLV12
Maximum working pressure: 230 bar
Maximum flow rate: 170 l/min
SYNCRO-PUMP
Grouting pumps
MIXTURE INJECTION
Once the TBM is reached, the Bi-component mixtures can be injected on the back of the concrete segments of the tunnel lining.
The filling of this annular void is carried out by means of small injectors, positioned inside the mechanized excavation equipment, in which the pressure and flow parameters can be managed very accurately through electro-controlled valves.
MCT Italy partners with Clivio Srl for the supply of the optimal type of grouting pumps, which most suitable for this application are the following: DP / OL4 and ID / OL2.
Clivio DP/OL4
TECHNICAL DATA
| Piston diameter | mm | 85 |
| Piston stroke | mm | 120 |
| Max strokes n. | Strokes p.m. | 85 |
| Pressure (LP) adjustable | bar | 0 – 40 |
| Delivery (LP) adjustable | litre p.m. | 0 – 30 |
| Maximum pressure (HP) | bar | 85 |
| Delivery (HP) | Litre p.m. | 9 |
| Inlet Mouth | gas | 1”1/2 |
| Outlet Mouth | gas | ¾” |
| Electric Power | kW | 3 |
| Length | mm | 750 |
| Width | mm | 500 |
| Height | mm | 1600 |
| Weight | kg | 190 |
Clivio ID/OL2
TECHNICAL DATA
| Piston diameter | mm | 85 |
| Piston stroke | mm | 125 |
| Max strokes n. | Strokes p.m. | 75 |
| Pressure (LP) adjustable | bar | 0 – 55 |
| Delivery (LP) adjustable | litre p.m. | 0 – 50 |
| Maximum pressure (HP) | bar | 90 |
| Delivery (HP) | Litre p.m. | 9 |
| Inlet Mouth | gas | 1”1/2 |
| Outlet Mouth | gas | ¾” |
| Electric Power | kW | 5,5 |
| Length | mm | 1050 |
| Width | mm | 690 |
| Height | mm | 1160 |
| Weight | kg | 290 |
Data monitoring and transmission
In the technology for back-filling systems, data recording systems are no longer seen as simple “data-loggers” but as a more complex and interconnected electronic management system.
All the equipment, in particular the mixing and pumping units, are equipped with electronic systems, connected and accessible from a single, remote interface, with the possibility of viewing, in real time, the data and operating parameters.
The electronic control system provides for the remote transmission of data, wireless mode, thus making them accessible remotely from distant offices and different operating locations, such as the TBM operations center.
The monitoring of pumping units usually controls the following parameters:
- Grouting Pressure
- Grouting Volume
- Grouting Flow-rate
The monitoring of mixing units usually controls the following parameters:
- W/C weighting
- Bentonite dosing
- Additives dosing
- Mixing time for each mixing cycle
- Number of the mixing cycles