Soil types in Israel: kurkar, expansive clay, loess and rock, and what they change in the quantities
Soil types in Israel change not only between the Negev and the coast, but sometimes within the same plot. For a quantity surveyor this is not only a geological matter: the type of soil decides whether there will be piles or a raft foundation, which drilling method is chosen, how much excavation and subbase there will be, and which tests go into the bill of quantities (BOQ). This page sums up the common soil types in Israel and what each of them tends to change in the quantities, at a general level only.
Soil types in Israel: a short map
- Kurkar and hamra, the coastal plain. The kurkar ridges are built of alternating layers of kurkar, a calcareous sandstone laid down by the wind, and hamra, an ancient soil (palaeosol). In the engineering literature kurkar is described as a partly cemented sand: cemented slabs of different sizes, scattered without order, with lenses of sand between them. So its properties usually change even within the same site.
- Sand. The main sand fields lie along the Mediterranean coast, in the north-western Negev and in the southern Arava. In government foundation tariffs, dense sand counts as normal ground conditions, and sand that is not dense counts as special conditions.
- Clay, and especially expansive clay. Expansive clay changes volume with moisture. A study from the Technion found that at the site it studied, most of the seasonal moisture changes took place in about the top 2.5 m, and in buildings built on clay the columns between the piles and the floor beams cracked. Another study showed that swelling can create tensile forces in the pile reinforcement.
- Loess, in the Negev. Loess soils are usually prone to collapse when they are wetted, and a planning appendix in the south noted that the low strength of loess needs attention in excavation.
- Limestone, dolomite and chalk, in the hill regions. In the limestone and dolomite of central Israel, the porosity is mainly solution channels and voids, in other words karst. A soil report published in the hill region stated that the strength of chalk drops with prolonged wetting, and that the chert (flint) inside it is very hard and wears down the drill bit.
- Basalt and basaltic soils, in the Golan and the eastern Galilee. Most of the Golan Heights is covered by basalt flows, and some of the soils derived from basalt have plastic horizons.
- Fill. Not a natural soil type, but very common on urban plots. One soil report noted that uncontrolled fill behind walls can settle by a few per cent of its thickness, and man-made fill is considered a soil that is particularly susceptible to liquefaction.
This division is general. There is no way to know what lies under a particular plot without a report for that plot, as explained on the page soil report and BOQ.
Which drilling method suits which soil
Bored piles are usually drilled dry as long as no groundwater or collapsing soil is met. When the sides of the bore are unstable, they are supported with a temporary casing or with bentonite slurry, which stabilises the side by hydrostatic pressure, and the concrete is poured through a pipe from the bottom up. One government soil report stated explicitly that the presence of water would require a switch to drilling with bentonite, and that is exactly the kind of sentence that changes an item in the bill.
In the CFA (continuous flight auger) method the concrete is pumped through the hollow stem of the auger, with no casing and no slurry, and the reinforcement is often limited to the upper part of the pile. The method is usually limited to soil and very weak rock, and conditions such as loose sand with shallow groundwater or voids in limestone do not suit it. In hard rock and boulders, core barrels and pneumatic hammers are used, and in karstic limestone and on sites with limited access, small-diameter micropiles are common. At a marine terminal on the coastal plain, driving steel piles through sandstone layers broke the slabs and required deeper driving than planned: an example of how even "stable" kurkar can surprise.
| Soil | Foundation or drilling method found in reports | What to check in the BOQ |
|---|---|---|
| Kurkar and hamra | Bored piles, sometimes with bentonite because of sand lenses | Two drilling alternatives, or a rule for switching between them |
| Sand with shallow groundwater | Casing or slurry; CFA less suitable | Dewatering items, piezometers and concrete placed below groundwater |
| Expansive clay | Piles taken below the swelling zone, suspended floor slab | Void formers under the slab instead of subbase, separating elements from the ground |
| Loess | Depends on the report; sensitive to wetting | Protection from wetting, subbase and controlled fill, compaction tests |
| Karstic limestone and chalk | Micropiles, hammer drilling, void filling | Extra over for drilling in rock, pile length set on site |
| Uncontrolled fill | Founding below the fill, or soil replacement | Soil replacement volume, removal, imported fill and compaction |
Every one of these lines has to be checked against the project's soil report and with the geotechnical consultant and the structural engineer. The table shows what usually appears in reports, not a recommendation for a particular project. More on the items themselves on the page excavation and shoring BOQ.
What each soil tends to change in the quantities
Soil types in Israel also differ in what they add to the bill. Expansive clay brings a suspended floor slab with it: published reports required every element that touches the ground to be separated from it by void formers, and the building's floor slab to be designed as a suspended slab over void formers. In the bill this means a longer piling chapter, void formers in m² instead of subbase in m³, and suspended ground beams. Sand and groundwater bring items for shoring, dewatering and concrete in wet conditions. Hard rock brings an extra over for rock breaking and drilling, and sometimes a pile length that is set only on site, in other words a quantity that is an estimate and is measured again during construction. Fill brings soil replacement and removal. On the difference between a design quantity and a quantity measured during construction, see the page physical quantity, BOQ quantity and order quantity.
A note on standards. Soil reports refer to the Israeli foundation standard and its clauses, for example the requirements for foundations in expansive soil. This page does not quote the wording of the standards, and any question about the requirements of the standard that apply to a project should go to the geotechnical consultant and the structural engineer.
What a professional quantity surveyor adds here
Measuring by the drawing alone will put into the bill the piles shown on the drawing, at the length shown on the drawing. A quantity surveyor who comes from the field, an engineer or a registered building technician who worked on site, like Yaakov Avital, also reads the soil report and asks whether the drawing and the report tell the same story. For example: the report describes expansive clay and recommends a suspended floor slab, while the structural drawing shows a slab on subbase in part of the building. Measuring by the drawing will put in a subbase. A professional check marks the gap as a question to the geotechnical consultant and the structural engineer, and they decide. The result is a flag, not a correction by the quantity surveyor. The work of a quantity surveyor for construction projects starts there, before a number goes into the bill.
The type of soil changes the earthworks quantity takeoff: expansive clay, kurkar and rock are excavated and removed differently. So the quantity calculation relies on the soil report for the plot, not on a regional average.
Frequently asked questions
How do you know which soil is on a plot?
Only from a soil report for the plot, with trial borings and tests. General maps and reports for neighbouring plots give a direction, not an answer, especially in kurkar, where the properties change within the site.
What is expansive clay and why is it a problem?
Clay that changes volume with moisture. The swelling lifts floor slabs and beams and can put the pile reinforcement in tension, so reports usually require a suspended floor slab and piles taken deeper, below the swelling zone.
What is CFA drilling?
Drilling with a continuous flight auger, with the concrete pumped through its hollow stem, with no casing and no slurry. When the conditions suit it, it is fast and economical, but it is limited to soil and weak rock and does not suit every site.
Does the soil type affect the price of the BOQ?
Not the price of the service, but the content of the bill: more alternatives, more items for testing and monitoring, and more quantities marked as estimates. The page construction cost estimate explains how such quantities are treated in a cost estimate.
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Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.