Phase 2: “Soft start” to site works (only where physical distancing can be maintained)
Phase 3: Steady state operation (only where physical distancing can be maintained)
Phase 4: Steady state operation (where physical distancing can be maintained and/or with PPE use)
Phase 5: Increasing density/productivity with experience
One week after, on May 29th the Government
announced that the no-essential works could start to move to Phase 1. Under
this phase, contractors can begin to prepare the sites to “facilitate the physical distancing and enhanced hygiene, including
Installing new or expanding existing site welfare and toilet facilities, “one
way” systems and marking 2m distancing throughout the site”.
During the first week of June, several companies [1][2][3]
have been adapting their sites to the next phase. However, even the health and
safety requirements are satisfied, progressing to Phase 2 is far from being automatic.
The government must be consulted before proceeding to the ‘soft start’ phase
(Phase 2), and it must be in line with public health advice. Also, Phase 2
will not take place until a minimum of 2
weeks after the updated advice is published. After more than one week of site preparations (from the 29thof
May), such announces have not been published yet, so it is unlikely to move to
the next phase in two weeks’ time.
Furthermore, most of the works will not be able to be
carried out in Phase 2. The guide remarks that in Phase 2 “no element of non-essential works requiring the use of PPE above the
standard industry use, will commence at this stage”. As I understand, the
soft start permits only a limited number of people to work when physical
distancing can be maintained, and no special coronavirus PPE is needed.
The details of phase 3 will be issued within the Phase 2
update. As well as the previous stage, in phase 3 only works than can ensure
physical distancing without the need of PPE could be carried out. It is
suggested that under this phase, only 30% or 40% of the original workforce will
be able to return depending on the site parameters. The objective of this phase
is monitoring a supervising the activity to reach a steady-state operation.
Therefore, the interchange of information between the sites and the Government
would be essential in this phase.
In Phase 4, PPE could be used to ensure physical distance,
and consequently, more workforce will be able to return to the sites. This
phase only will be possible if the supply of the PPE equipment is guaranteed. Around
10% of the original workforce is expected to return thanks to the use of PPE, which
means 40-50% of workers on site.
Lastly, in Phase 5, the workforce will be increased progressively
based on the experience gathered in the previous phases.
The guide sets a long journey for sites to return safely to
work as we remember. According to the MSP Kevin Stewart, progress beyond these stages will clearly depend on a range of factors,
including the industry’s ability to demonstrate fully compliant working
practices in place, the confidence of the workforce and its trade union
representatives in those arrangements, and wider supporting health data.
The following image summarizes the re-start model.
While construction firms in England, Wales and Northern
Ireland have been “actively encouraged” to re-open the construction sites
(with safety measures in place), the categorized as non-essential works in Scotland
remain closed up to date. The Scottish Government considered necessary a 6-step
phased approach to re-open the non-essential sites safely, a progressive
approach that takes more time to re-open the sites.
The divergence among approaches lies in the top priority set
by the Scottish Government: guarantee the safety and wellbeing of the
construction workers and the country. The Government considers the construction
sector and its supply chain a non-essential business sector, except when
supporting an essential or strategic activity for the country as could be energy projects,
maintenance operations or repairs. Consequently, the non-essential projects
must adhere to a “slow and steady” guided re-opening process in order to contain
the COVID-19 spread. However, how is the Government putting into practice this approach
against the economic pressures for an immediate re-opening?
It must be said that the Scottish Government did not force
by law to close the construction sites. The Government is relying on
the goodwill of the industry to follow their guidance instead of imposing an
instruction upon them. However, new health and safety requirements to deal with
the COVID-19 in the workplace are obligatory and forced by law, and then, the
police have the power to enforce these obligations.
Even the Government is not forcing to shut down
non-essential sites; it is hard to image re-opening a site against the
Government advice. The scenario is far to be appealing: supply and services
shortage as the majority of the industry is shut down, bad press for
contradicting the public advice and high health and safety risk assumed are
only a few examples.
The Scottish Government position of not enforcing the site’s
lockdown could open a debate about who is responsible for the delay and cost of
shutdown. Even several public authorities are implementing measures to help
the industry under these extraordinary circumstances (like the job retention and
business interruption loan schemes), the government is not openly assuming the
responsibility and then eluding a strict compromise.
According to the letter from the Kevin Stewart MSP on the 21st
of May, the coronavirus construction guidance is a consensual decision between the
stakeholders. The arrangement between the parts seems sensible; The Government
agrees to help the industry to follow the guidelines and the industry accept to
apply it. Then, in certain terms, the Government is accountable.
Another issue is the lack of resources of the public authorities
to enforce the requirements on sites. I found quite intelligent to involve
the industry in such a strategy instead of forcing them. If the industry as a
whole takes an active part in the re-opening process, it is more likely that
the companies embrace the guidance and its philosophy. Still, the Government is
relying on the cooperation of the industry.
There is still a long way until we see the effectiveness of
the approaches on both sides of the border. Under this approach, the Scottish Government
has the challenge of keeping the commitment of the industry to re-open the non-essential
sites as planned and, this commitment only will be possible if the financial
support to the companies meets their needs and arrives on time. By now, the
time is running against the Scottish side, but maybe the price paid is too
high for those who went for a quick recovery.
According to Scottish Water, in Scotland gravity sewers must be inspected and tested in two stages: as the work precedes and after backfilling sewer line. The checks requested in Sewers for Scotland (Scottish Water, 2018) follow the advice on testing requirements of BS EN 1610:2015 “Construction and Testing of Drains and Sewers”. Actually, the testing requirements for sewers for the UK are also based on the same British Standard, and consequently, the checking procedures are identical (Water UK, 2018).
The tests done after laying the pipes and before backfilling or concreting are done to ensure the correct assembly of joins and detecting possible workmanship and site handling damage.
Test performed after backfilling may guarantee that the sewers have not been compromised during the completion of the works and meet all the standards. Also, the testing process entails the contractor to clean the sewers before the handling.
Scottish Water in Sewers for Scotland V.4 (2018) requests the successful completion of the following tests/inspections for gravity sewers (foul and storm lines):
Test as the work precedes:
Air or water test (clauses 4.7.4. and 4.7.5. respectively).
Tests after backfilling:
Air test of the sewer line (between manholes) (Cause 4.7.4.)
Visual inspection: CCTV survey (Clause 4.7.6)
Infiltration (Clause 4.7.7)
Water-tightness (Clause 4.7.8)
As follows, all the tests on the previous list are briefly described highlighting some aspects that help me to understand better these practices. I have not entered into detail, for further information is recommended to consult the official codes and guidance (references).
Tests as the work precedes
Air test for gravity sewers
The industry prefers the air test than the water test because it is less time demanding, more straight forward and avoids additional safety precautions needed when using the higher test pressures. Both of them serve the same purpose, and the acceptance of the sewers entails pass only one of them.
The test consists of blocking all the inlets of the sewer line tested and check if the pipes assembled could maintain a pressure of 100mm head of water pumped into the system for 5 minutes. The test is successful if the air pressure remains above 75 mm head of water after these 5 minutes.
There are two reasons why the test is done before backfilling: first, to be able to solve any deficiencies on time and second, because the test could be not valid due to possible water infiltration after backfilling.
A sewer is only accepted if the sewer passes the test. If not, the contractor should find and correct the issue and repeat the test. However, failure to pass this test is not conclusive; the test could give a fake fail. It is essential to ensure that the testing process is carried out correctly. Some reasons for a false test failure could be the following ones:
Damaged equipment.
Installation of the test equipment. For example leaks on the connections, valves not closed correctly or Inflatable Stoppers against the inside of the pipe not wholly sealing the pipe.
Insufficient time for stabilisation: Temperature and weather has a substantial effect on the test and stabilisation. In conditions of hot weather, due to the expansion of the air when heated, more stabilisation time could be required. On the other hand, testing below 1 Celsius degree could result in a significant loss of pressure during the test and the consequent test failure. In this case, more stabilisation time could be needed as well.
Sewers shall be tested regularly throughout the installation before any concreting or backfilling. Sewers for adoption (Water UK, 2018) recommends every three jointed segments (clause E7.3.2), but it could be done every 3 or 5 pipes. In general, it is recommended to test all the line before constructing the manholes in the extremes.
Lastly, I would like to highlight that the test is more severe for short and small pipelines than pipelines long with large diameters. The air test requests the same pressure requirements (pressure above 75mm head of water after 5 min) regardless of the diameter and length of the pipeline. As a consequence, in a short run of small diameter pipes that contains small air volume, minor loses of air will drop the pressure quickly, and then, it is easy to fail the test. It is recommended to do the test every 4 or 5 pipes for small pipes diameters (>150mm) to increase the volume of air tested and avoid the over-severity of this test.
Water test for gravity sewers
The water test has the same purpose and philosophy than the air test: testing the water-tightness capacity of the sewer by measuring the loses of fluid in a pressured set of pipes.
In this case, water is the fluid used instead of air to give pressure. The pipes should be filled with water until the pipeline contains no less than 1 m head of water over the soffit of the highest point. The pressure in the pipeline’s lowest point always must be lower than 5m head of water. In such cases the pressure is more than 5m head in the bottom of the line, the pipeline should be tested on several stages.
The water test takes long to stabilise before proceeding. The pipeline should be filled with water over an hour to allow the absorption of water by the pipe material. Once the system is wet, the water level should be restored.
The test consists of measure the water needed to maintain the water level (and the pressure) above 1 m head of water in the top of the pipeline. During the test, the water level is restored every 5 minutes, writing down the litres of water added. If the loses in 30 min do not excess 0.5 litres/m3, the pipeline passes the test.
This test is more tedious and time-consuming than the air test but takes into account the difference of diameter and length of the pipeline setting different parameter. Also, the leaks are easy to detect.
Tests after backfilling
Air test of the sewer line
After backfilling, the pipeline should be Air tested again from manhole to manhole. This last air test is to ensure that the pipeline has not been compromised during the backfilling works, especially when compacting.
Visual inspection
The visual inspection usually includes the use of a CCTV survey and a light-line inspection that use light rings to measure deformations. All the net should be completely clean to carry out the visual inspection. Usually, the net is cleaned with water pressure and dewatered before the inspection.
The CCTV survey film any infiltration on the system, so it supports the infiltration and Water-tightness verification.
Infiltration
The pipelines and manholes should be accepted as satisfactory if the infiltration, including the infiltration into manholes, does not exceed 0,2 litres/m2 in 30 min, where m2 refers to the total internal surface area of the pipeline and manholes.
To perform this test, all inlets of the system shall be effectively blocked and any residual flow should be deemed to be infiltration.
Water-tightness
No discernible water flow penetration into the manholes and chambers should be detected. This could be checked when conducting the visual inspection and infiltration tests.
References:
Scottish Water, Sewers for Scotland – A technical specification for the design and construction of sewerage infrastructure, Version 4.0 – October 2018
Water UK, Sewers for Adoption – A Design and Construction Guide for Developers, Eighth edition – August 2018.
BS EN 1610:2015, Construction and testing of drains and sewers, September 2015
