Works Examples»Dig Safe Tuesday, September 19, 2017





According to the principle of pneumatic transport each material can be carried when it is suspended in the atmosphere. Air volume has to be bigger than the volume of the sediment, because there is a huge difference between the specific weight of the air and the sediment.

The applications of this principle are in the building, sewer and road maintenance.
The equipment is required in delicate contexts and where there are several technical difficulties because of the narrowness and typology of space. It is particularly useful where some conditions rule out the use or limit the use of mechanical machines.

Since about ten years, in Italy, the application of air in maintenance works is more and more frequent and widespread.
The technology uses a powerful turbine aspirator, named suction excavator, mounted on vehicles and self-moving machines. Main features of these machines are their speed in finishing operations and the reduction of manual works.



One of the most important problem to the maintenance of water, phone, gas utilities is the excavation in urban areas. Every yard implies problems to the traffic, noise pollution, restoration of the paving, and it is difficult to preserve the pre-existing constructions.

The problem is bigger and bigger when there is the necessity of many small diggings. This kind of work implies the use of more companies able to operate twenty-four hours a day and this is very expensive. To operate and solve the various problems of waterworks maintenance company proposes to municipalities and administration bodies the method of the suction excavation to achieve the following aims:
-Time reduction of the excavation (70% than traditional methods)
-Excavation volume reduction
-Reduction of the space occupied in the working area
-Complete absence of debris and muddy material around and in the excavation site.

Pneumatic Excavation:
The paving is cut with the traditional pneumatic tools given with the equipment.

Picture 1: Digging in urban area

Picture 2: Initial phase of digging

The earth is crushed using the earth-breaking lance and pneumatic air jet lance which substitute pick and shovel of the operator.

Picture 3: Pneumatic air jet lance functioning

Picture 4: Use of the pneumatic air jet lance


The dug earth, through suction, is removed and carried, through the suction hose, in a storage tank, while the air is put back to the atmosphere.

Main Components of PneumaticTransport Equipment:
Air generator: a heat engine or electromotor starts a fan, a booster which creates an air flow.

Product carrier: when the suction operation begins the material that has to be carried begins to move towards its destination inside a pipe.
Extraction system of the product from the air: products are collected in a dump storage tank, while the air is put back to the atmosphere.

In this system the dug earth is torn up and carried through an air flow at high speed.

Main parameters:
Air flow QMF (mc/s or mc/h) describes the air volume per unit of time to ensure the flow of the material.
Dug earth capacity QMP (kg/s or kg/h or T/h) describes the quantity of the material carried per unit of time.
Cm concentration describes the relation between the air and the material flow:
Air speed VF (m/s) describes the average speed of air needed to carry in a specific point and in a particular moment. It is difficult to calculate directly the speed; generally it is calculated knowing the capacity.
Functioning depression P (17000 Pa) it is the depression used by the equipment.
The readings of these parameters are changed thanks to the experience with this equipment and at the moment they are as follows:
- Nominal capacity of operation: 2500 mc/h
- Minimum theoretical speed of air in the flexible hose: 500km/h
- Flexible hose diameter: 250 mm
Components of the System
Motorization and transmission
With the engine of the vehicle. In this solution there is a gearbox on the transmission shaft which can be disconnected. This system has the advantage to reduce the weight and space occupied by the vehicle, to make easier the maintenance, and to decrease the price.
Storage and settling tank
The capacity, about 8mc, has been adopted to solve the initial problem of having many small diggings in urban areas together with operations from the edge of the excavation..
Thanks to this solution the material is unloaded by a dump tank, without any manual operating.
Dust filter  
The settling tank could not perfectly filter the sucked fluid, so it has been necessary to conceive a filter system to respect the regulation about the emission into the atmosphere.
Suction hose
The flexible hose chosen has the following features:
Low weight to be easy to maintain
Flexibility and resistance to knocks and abrasions also at low atmospheric temperature
Low sensibility to obstructions
At its end it has a steel element of a smaller diameter which can be removed. The entry of sucked materials in the tank is conceived to avoid obstructions. The length depends on the condition of the work. The hose is supported by a telescopic arm radio controlled (up and down) rotating on an axis. 
The sucking hose together with the arm is conceived to be placed in the correct position for the traffic without removing the hose. An ergonomic wheel with all the controls is fixed in the hose in a removable way in order to handle it in every situations from the edge of the excavation.

Economic aspects
The advantages in the use of the suction excavator are various and some of them cannot be directly measured. For instance:
Small risk to damage underground pipes;
Less disturbance to residents who lives and pass in the area;
More efficiency;
More supply of excavators;
- The possibility to make preventive operations.
The only elements that can be measured are based above all not only on the decrease of dug earth volume but also the surface of the paving that has to be restored.
Several studies in this field concern with the comparison between the cost of a yard which uses the method of the suction excavation and the techniques of operations from the edge of the digging, and the cost of the same yard using the traditional method. After an analysis of the different elements, such as the hour profit per yard and the profit rate, results that the saving is significant and it can reach a value of about 30%-60% and more for some works.

Picture 5 : Economic efficiency


Manual Excavation
1. Manual excavation, normal soil conditions,
    presence of buried cables and pipes

Employing Suction Excavator for removing

2. Heavy soil, presence of buried cables and pipes
3. Dry and heavy soil
4. Wet and heavy soil or clay
5. Moderately heavy soil
6. Muddy soil, gravel and crushed rock
7. Sandy soil
8. Water

- Vehicle transfer speed;
Reduction of the space occupied in the working area;
Reduction of the excavation volume (from 40% to 60%);
Working time reduction (from 40% to 70%);
Excavation, loading and carrying with only one machine;
Suction of every kind of materials (dry, liquid, muddy, gravelly);
No use of shovel;
No damages to underground pipes and lines;
Dry excavation even in the presence of seepage from other channels;
Machine supplied with many tools (air compressor, demolishing hammer, rammer, pneumatic air jet lance, “lombrico” mini-digger);
Complete absence of debris and muddy material around and in the excavation site;
Each operation is made by a radio control at the edge of the hole;
Possibility to unload the dug earth on dump containers;
Excavation speed proportional to the friability of the materials;
Practicalness to silting-up excavations to drillings and Inspections to the condition of channels, connections, joints;
- Many operations can be acted even with networks operating;
Reduction of insurance costs (no breaks-no franchise);
Maximum safety in the presence of gas and sewer exhalation.
Rio Terà S.Polo
In the last years the delicate Venetian ecosystem has underlined the maintenance and cleaning issues of “rii tera’”. During XVIII and XIX century, above all under the Austrian domination, the “rii tera’” have been transformed in pedestrian crossing thanks to interments and coverings.
During XVII century Riello delle Erbe was completely covered because of the unstable water flow and frequent silting up. In this way water was forced through underground channel with a semicircular vault built entirely of brick. Over the last two centuries, up until 1963, the channel, known as Rio Tera’ San Polo, was occasionally cleaned in order to remove mud and debris which inevitably clogged it.
The removal of the sediment, caused by water stagnation in pipes and covered canals, is a problem involving operational difficulties and important expenditure. The environmental conditions do not permit to use or limit the use of ordinary machines, both mechanical and manual. Moreover digging in channels with traditional methods oblige to work in underground and unhealthy environment. Other more advanced systems which use scraping buckets need big spaces and cause troubles to pedestrians and residents because of the noise and smell.

Picture 6: Suction yard

After almost forty years from the last digging Insula, together with Gerotto Federico company, planned and acted a cleaning operation which has freed the obstructed rio tera’ San Polo. For the first time Insula used in the Venetian historic centre an innovative technology of mud removal.
It consists in a modular system created to have an appropriate distribution of weight in order to be moved in the narrow spaces of Venice, first by boats and then in pavements of limited capacity.
Through an opening in the underground vault and through the paving on top this equipment activates a fan which sucks the silt removed by an hydraulic mini-digger in a watertight tank. From here the mud is pumped in a pipe which carry it directly to a barge moored at Fondamenta delle Erbe far from the yard (about 80m). In the last phase the silt is carried through barges to an authorised dump. 

Picture 7: Thickness of the sediment

The operation involved the following stages:
Creation of cofferdams at two points, in rio delle Erbe and riello Sant’Antonio, to enable the drying of the entire underground channel.
Cleaning of the main channel without intermediate cofferdams. For the safety of workers and to have a continuos change of air there were no blocks with sluice gates along the longitudinal axis.
In the pavement on top of the vault four openings of limited dimensions have been acted to introduce the suction and mud removal equipment. At the end of the work these openings have been closed by manhole covers to have an easy entry to the channel in the future.
Unloading of the material with the methods explained above and the use of the suction excavation

Picture 8: Thickness of the sediment

Picture 9: Emptied and restored vault

Rio S.Leonardo
An other example of channel reactivation is that of rio terà S. Leonardo (230m long and 6-13m wide). It is one of the busiest thoroughfare of Venice. Its width permits to frontagers thriving trade and the use of the square shared with the permanent local market.
During the works of sewer maintenance and paving restoration it was verified the precarious state of channels which could, because of the new works, risk their functioning with consequent dangerous irregular reflow and problems to public health and buildings. The main underground channel, a brick vault 1,6 m wide, was completely full of sediments (mud height 1,60m) avoiding regular water flow.
Therefore it was necessary to reactivate as soon as possible, at least partially, the hydraulic functioning of the channel (ending part 1,10m).

Picture 10:  Dry cleaning pipe system (A: suction equipement, B: video controlled mini digger, C: suction house)

It was used the suction excavation method. The yard with the suction equipment was placed at the end of rio terà S. Leonardo occupying a central part of rio terà Farsetti (6m wide 30m long), that is only 1\10 of the space occupied by a traditional yard.
The channel was drainned closing with a cofferdam Canal de Cannaregio and maintained dry by an automatic draught pump.
The speed and the reduction in the number of operators have been the main features of this method. The work was well-done cleaning completely the vault without further manual finishing.
The channel was emptided using the same method of Rio Terà S.Polo thanks to a video-controlled suction mini digger.

Picture 11: Position of Suction Excavator
This technique has accelerated the operations of debris removal improving the working conditions for operators and limiting physical contact with debris. Moreover this method did not disturb the life of the city, because the traffic was not diverted and the traditional market took place as usual.

This work underlines the compatibility of the suction technology with the delicate historic structure. The aim was to empty debris from vaults and demolished overstructures. It has been used a forked suction hose in order to work with four operators: two for every suction point, one to move the material which was sometimes compacted and the other at the top of the suction hose.

Picture 12: Suction phases
Palazzo della Ragione
The south loggia of Palazzo della Ragione (1218, AD) in Padua has been restored. The suction excavator was used to remove guano, rubble, and dust in the loft of the loggia.
Only one small-size access was practicable in the intrados of the vaults. The suction excavator was located in Piazza delle Erbe from where started the very light hose, 150m long, to pass through the access and then to run along the extrados of the vault.
The air filter system, placed inside the suction tank, assured the absence of dust during the operations. In this way the debris has been sucked where it was produced and then unloaded in cofferdams and authorised dumps.

Picture 13: Position of the Suction Excavator

Picture 14: Rubble Suction

The underground of the city of Siena is full of tunnels excavated in tuff which have been filled up with rubble and other materials during the restoration phases of old buildings.
The operation consisted in the removal of about 150mc of rubble. The two axis mini suction excavator was located in a particular position in order to unload rubble on a small truck (3.5 ton) which carried it in storage areas.
The suction hose went down for about 10m through a hole in the flooring of the ground storey removing the material in safety working conditions.

Picture 15: Position of mini suction

Picture 16: Inside Tunnels during cleaning phases


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