Implementation methods for dealing with groundwater on site (piles and slurry wall)
Feb 16, 2023
From: Omri Nissany, Civil Engineer and Licensed Insurance Agent
Second article in the series
Dealing with groundwater on construction sites in Israel is a common and well-known issue. Especially when we talk about the large number of projects in the central region located above the coastal aquifer and are also aware of the housing and parking shortage, which is a key consideration in planning with deep excavations.
In the following short article, we will discuss the two common construction methods for constructing retaining walls on construction sites in Israel and touch on risk and insurance aspects related to groundwater in the construction industry.
From: Omri Nissany, Civil Engineer and Licensed Insurance Agent
Second article in the series
Dealing with groundwater on construction sites in Israel is a common and well-known issue. Especially when we talk about the large number of projects in the central region located above the coastal aquifer and are also aware of the housing and parking shortage, which is a key consideration in planning with deep excavations.
In the following short article, we will discuss the two common construction methods for constructing retaining walls on construction sites in Israel and touch on risk and insurance aspects related to groundwater in the construction industry.
Groundwater Degradation with Slurry Wall and Piles
The two main construction methods for constructing retaining walls are the slurry wall technique and the pile technique. The slurry wall technique is considered the preferred technique for treating groundwater, but its cost is higher than the pile technique.
The slurry wall technique is used to cast reinforced concrete lining walls. This is with the aim of creating as much protection as possible against the ingress of water that is close to the surface. The slurry wall acts as a water barrier (diaphragm) on the walls of the underground pit and stabilizes them for further castings.
By the way, a slurry wall is a solution designed not only for dealing with groundwater but also for other applications such as demarcating the site from tunnels or nearby underground structures.
In addition to the lining walls, "site floor" solutions are implemented, such as jet grout or deep penetration of the slurry wall into the ground using the clay layer as a natural plug.
The pile-driving method, on the other hand, is available at lower budgets and is based on drilling, after which concrete and a reinforcement cage are inserted into the borehole. Concrete is then sprayed at each storey drop, and sometimes even full spraying is done along the entire length of the borehole. In pile-driving methods, unlike the slurry wall, there will be certain gaps in the wall, and if the application is not carried out properly, events such as landslides, the formation of sinkholes under nearby buildings, and even collapse on the site itself may occur.
Lining a construction site is an integral part of a project with significant excavation. When it is also a lining designed to deal with groundwater, the risks increase significantly.
The two main construction methods for constructing retaining walls are the slurry wall technique and the pile technique. The slurry wall technique is considered the preferred technique for treating groundwater, but its cost is higher than the pile technique.
The slurry wall technique is used to cast reinforced concrete lining walls. This is with the aim of creating as much protection as possible against the ingress of water that is close to the surface. The slurry wall acts as a water barrier (diaphragm) on the walls of the underground pit and stabilizes them for further castings.
By the way, a slurry wall is a solution designed not only for dealing with groundwater but also for other applications such as demarcating the site from tunnels or nearby underground structures.
In addition to the lining walls, "site floor" solutions are implemented, such as jet grout or deep penetration of the slurry wall into the ground using the clay layer as a natural plug.
The pile-driving method, on the other hand, is available at lower budgets and is based on drilling, after which concrete and a reinforcement cage are inserted into the borehole. Concrete is then sprayed at each storey drop, and sometimes even full spraying is done along the entire length of the borehole. In pile-driving methods, unlike the slurry wall, there will be certain gaps in the wall, and if the application is not carried out properly, events such as landslides, the formation of sinkholes under nearby buildings, and even collapse on the site itself may occur.
Lining a construction site is an integral part of a project with significant excavation. When it is also a lining designed to deal with groundwater, the risks increase significantly.
In recent years, there have been quite a few changes, some of them dramatic, in the construction insurance market in Israel. Without going into detail, we will mention that overseas reinsurers have significantly tightened their terms with Israeli insurance companies, which are also tightening their belts.
When it comes to projects that require groundwater depletion, insurance companies often view this as an extremely high risk, especially if the excavation is particularly deep and reaches "high-risk" levels.
As a result, insurance companies are making difficult demands on policyholders. Starting from the requirement to hire an expert and experienced water degradation contractor to the requirement to hire a main contractor with experience in similar projects. Similarly, there has been an increase in excesses, and these are not small amounts, but rather an increase that reaches hundreds of thousands of shekels and even over a million shekels. Of course, rejecting a project for insurance entirely is also common today, and often contractor work insurance is offered that comprehensively excludes any damage from groundwater.
The insurance companies' perspective – not at any cost
These aspects further emphasize the need for professional assistance and close support from an insurance agency with extensive experience in the field of construction insurance. That is, an insurance agency that understands the insurance and engineering nuances, is familiar with the various execution methods, and is familiar with the diverse risks.
Contacting an agency that is not sufficiently experienced may lead to an insurance rejection that will be difficult (or impossible) to reverse later.
There are many steps that should be taken into consideration when submitting an insurance application. One of the most prominent is the preparation of a soil report by a consultant who will determine the expected change in the water level (usually at a level of plus or minus two meters). Please note that it is highly desirable that the soil report be up-to-date , as the groundwater level is dynamic and changes, both due to subsidence in the area and due to geological or seasonal events.
If it turns out that there is a risk of groundwater intrusion and there is no choice but to carry out the lowering, the insurance company will even demand to see a detailed hydrological report . A report that presents the current situation and the proposed solutions. It is very important that the insured's representative who meets with the insurance company surveyor be familiar with all the details and implementation processes (not only in terms of lowering the groundwater but also with regard to the details of the excavation, lining, etc.). This is to minimize the chance of the project being rejected for insurance or introducing exceptions to the insurance coverage in the policy.
Skilled professional assistance
Groundwater can cause considerable damage to a construction site and even to nearby structures. One of the most common situations is when groundwater breaks out and the contractor is unable to control it. Either because the pump supply on site is insufficient or – in more serious cases – the break is unexpected and there is no effective pumping function at all.
The groundwater breach may cause, first and foremost, damage to the works themselves, to the point of collapsing piles and foundations that are washed away by the water flow. There is also a real risk of damage to neighboring structures due to the violation of the "hydrological balance" in the vicinity of the site, as well as causing landslides and/or the appearance of dangerous sinkholes. In addition, of course, such events endanger the site workers.
What damage can be caused to the construction site and its surroundings as a result of a groundwater eruption?
In conclusion,
Dealing with groundwater on construction sites is related to the execution method chosen in the specific case, the depth of groundwater penetration - and the insurance coverage that exists (or does not exist) for the risks expected in the project against an unexpected (or expected) groundwater event on the site.
To read the first article in the series, click the link
To read the third article in the series, click the link
To read the fourth article in the series Link
Dealing with groundwater on construction sites is related to the execution method chosen in the specific case, the depth of groundwater penetration - and the insurance coverage that exists (or does not exist) for the risks expected in the project against an unexpected (or expected) groundwater event on the site.
To read the first article in the series, click the link
To read the third article in the series, click the link
To read the fourth article in the series Link
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