Another advantage of London Clay is that, clay being impermeable, groundwater does not penetrate into the tunnels. The London Clay is nearer the ground surface north of the River Thames, and this is why the Tube is much more extensive on the north side of the river compared with the south side.
Is London Clay permeable?
London Clay is also used to line exhausted quarries. This is because old quarry holes are generally refilled with waste material and by lining it with London Clay (which is virtually impermeable) it prevents waste and hazardous substances from entering the groundwater.
Is London Clay good to build on?
Properties built on clay soils are vulnerable to subsidence because the soils are more likely to shrink when they are dry. Many London properties are built on London Clay, which is notorious for shrinking as it dries out.
What is under London Clay?
The London Clay mainly comprises bioturbated or poorly laminated, blue-grey or grey-brown, slightly calcareous, silty to very silty clay, clayey silt and sometimes silt, with some layers of sandy clay. It commonly contains thin courses of carbonate concretions (‘cementstone nodules’) and disseminated pyrite.
Is London Clay overconsolidated?
Modelling failure of London Clay is significantly more complex due to its overconsolidated and fissured nature.
Is clay a good water barrier?
As water molecules bond to clay particles, the clay expands, filling cracks and gaps in the foundation so that water can’t get in. Like any exterior waterproofing system, bentonite waterproofing is more effective and more affordable when applied during new construction.
Does water drain through clay?
Clay soil forms tight layers that won’t allow drainage. This means that, after precipitation, drainage issues will most likely present themselves. Many building contractors will use heavy machinery that will compact the soil and break down the soil structure, destroying the air pockets that allow for drainage.
Is London Clay shrinkable?
3D volume-change potential mapping, London
All clays are susceptible to some shrinkage and swelling due to changes in moisture content. Those with a higher proportion of expansive clay minerals, such as smectite, are even more prone.
Is it OK to build a house on clay soil?
Clay soil isn’t particularly good for construction because it’s susceptible to moisture fluctuation. It expands when it’s moist and contracts when it’s dry, resulting in uneven floors and fissures in the foundation. Clay creates poor soil support, and you’d need a proper structural foundation to keep it stable.
How deep is the clay under London?
433 feet
London Clay, lies up to 433 feet (132 metres) thick under the City of London and supports most of its tunnels and deeper foundations.
Why is London built on clay?
The Ice Ages and more recent deposits
At the height of the last ice age as recently as 20,000 years ago, the ice sheet, extended down to present day Finchley, and deposited boulder clay around Finchley and much of London to the north.
How thick is London Clay?
London Clay is about 45 metres thick under Westminster, and overlies the chalk. In places it’s more than 150 metres thick.
Are there secret tunnels under London?
Beneath London’s bustling cities lies a mysterious world of Cold War-era tunnel systems and underground chambers – these number in the hundreds. Many of these are owned by the Ministry of Defense and have never been publicly acknowledged – and until recently authorities remained secretive about them.
What PH is London Clay?
7.5 to 10
Clay soil usually leans towards the alkaline side with PH levels ranging for 7.5 to 10 or so.
How do you know if soil is Overconsolidated?
Overconsolidation. If the current state of soil is on the normal compression line it is said to be normally consolidated. If the soil is unloaded it becomes overconsolidated. Soil cannot usually be at a state outside the normal compression line unless it is bonded or structured.
Is London Clay firm?
Intact, unweathered London Clay is often described as stiff becoming very stiff with depth fissured blue clay, while the weathered material is usually firm and brown as a consequence of the oxidisation process (Chandler and Apted, 1988). For decades it has mostly been regarded as a uniform and homogeneous material.
What are the disadvantages of clay?
Disadvantages of Clay Soils
- Holds onto water, slow to drain.
- Slow to warm in the spring.
- Compacts easily.
- Tends to be alkaline.
What types of clay are waterproof?
Polymer clay IS waterproof after baking. Polymer clay comes pre-colored and is used to make small craft projects because it works great for intricate details.
What holds water better clay or sand?
Clay particles have the ability to physically and chemically “hold” water molecules to the particle more tightly than sands or silts. Sands “give up” the water between the pores much easier than silts or clays.
How long does it take for water to pass through clay?
A clay-loam generally allows water to move through surface particles at a rate of 0.1 – 0.2 inches per hour.
What happens if clay touches water?
(1) Hydration occurs as clay packets absorb water and swell. (2) Dispersion (or disaggregation) causes clay platelets to break apart and disperse into the water due to loss of attractive forces as water forces the platelets farther apart.