foundation for pharmaceutical plant !

[spc268]

Hi There! We are building a pharmaceutical plant near the seaside in Europe....the site is made ground over estuarine and marine alluvial, over weak rocks, clays and sands of the mercia mudstone group with alluvial sands and mercia mudstone group. Base on the SI report we suggested to our client the use of vibro concrete columns for the process area which will be heavily loaded with super heavy process equipment but was rejected by the client coz they said that they worry about the cost and the settlement of the clay in long run...was wondering do you guys have any suggestion? Me and my mates here are struggling to come up with a good foundation design for our boss

 

[gandersen]

spc268:

Could you give a little more details about the thicknesses of the various soil strata and the depth to the more competent materials, strength of the more competent materials, etc.?

 

[VAD]

Hello spc268

I presume that the recommendations are that the piles should be embedded in the mudstone. Would precast or prestressed concrete piles be less costly?. Alternatively H-piles may be desirable. As Gandersen said some more information is required. How far are you from the seaside.? as this has an influence on concrete cover to steel etc. What piles are commonly used in the general area?.

 

[spc268]

Site description:

The site consist of a roughly rectangular area of land approximately 90 m by 70 m. There are grasses areas to the north and west. To the south is a grassed area approximately 100 m wide, beyond which is the access road to the site. The site is generally leveal apart from a few hummocks approximately 1 m high at the northern end of the site. The area is presently divided by a chainlink fence. To the south the site has a recent covering of hardcore which is expected to be for a contractors compound.

Ground conditions:

Groundwater level is very shallow and tidal.

surface layer of compacted hardcore (crushed concrete and brick at one location, dolomite at the other)

0.5 to 1.0m -----------------------------------------
loose hydraulically-placed sand
between 2.0 and 3.0m ---------------------------------
organic black silt (alluvium)
between 4.2 amd 5.2m ---------------------------------
Alluvial sands
between 11.3 and 14.5m ------------------------------
Glacial Till, mostly stiff clays,
but with layers of dense sands and
gravels with cobbles
about 28.5 m ---------------------------------------------
Mudstone bedrock

The site is located not more than 2km away from the sea...the site is located between a main road and the edge of the north sea

 

[VAD]

Thanks for info. Based on what I see, I am not sure about the settlement concern. Is additional fill to be placed on site. Piles with toe in Glacial Till would seem appropriate. How deep are your vibro columns expected to go?.

I would go for driven H piles. Pipe piles may reach the till layer but embedment into the till may not be large. Drilled shaft would require to be cased as hole is advanced which increases cost of pile but one can achieve deeper depths such as toe in bedrock.

Thats all for now

 

[BigH]

How loose are the alluvial sands? What is between the alluvial sands and the glacial till? Or, are these the thicknesses of each layer rather than depth. If sands are compact, why not just remove the upper 4m and replace with sand fill (assuming that 4m would get you down to the alluvial sands). The final analysis would be to determine if the cost of removal (and I understand that the water level is "high&quot is more than the piles and associated pile caps.

If you go piles into the till, my preference would be closed end steel tube piles - say 250mm to 300mm diameter (that is what I've normally used into till) rather than H-piles. Sometimes H-piles have a tendency to go rather much deeper on redriving.

 

[Focht3]

I, too, would go for closed end pipe piles. You can inspect them (from the inside) after they have been driven, and they can be filled with concrete if there is a concern over integrity or compressibility after driving.

If you want to get to the bedrock, you will have to use drilled piers, not driven piles. The glacial till could cause real problems trying to drive piles all the way through - not a good risk for a high value facility that is sensitive to movement.

Yet a shallow foundation system - or combination of shallow foundations and "deep" piles/piers - could be made to work quite well. The real problem with remove and replace isn't technical - it's the size of the property. If the whole site is only 70m by 90m, you don't have room for this approach. I hope those dimensions are simply the building's footprint -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[spc268]

Basically we have made ground over the alluvial sands and clay beneath the alluvial sands. Our main concern is the high water table which may cause a serious problem....if we would go for steel or concrete piles wouldn't the high water table be an issue? At the moment we are considering vibro stone column and vibro compaction on the saturated soil but we are not sure about the cost of these methods, do you guys know anything about it? Do you guys think this approach would work?

By the way, I apologize about the previous figure..the size for the site is approximately 160m by 160m. I'll fill you all in on further SI info once I check with the geotechnical team.

Thanks for the advices guys!

 

[BigH]

I don't see a problem with closed end piles in high water table subject to trafficking of the pile driving equipment. I've done it adjacent to Lake Michigan in northern Michigan.

 

[Robert168]

I have a particular interest in the sand layer of 4.2 to 5.2 meters in (thickness?), especially its density.

If it is of high density, I would use it as the bearing layer for short piles, specially when the site is not in the area with high earthquake tensity and the superstructure not a monster(no liquefaction probblem and no excessive settlement).

However, if it is a loose sand, I will be happy to follow the suggestions provided by the epxerts, having piles seated on either the glacial till or the bedrock depending on the bearing capacity and settlement limit required of the piles.

 

[VAD]

Robert 168 has brought up a good point re liquefaction of the deposit. I get the feeling that this may be why the vibro stone column treatment is being addressed. This type of foundation has the ability to dissipate pore water pressures quickly in liquefaction situations. Perhaps there is more than just choosing a pile to carry a certain vertical load.

I would be interested to see some geotechnical information on the various soil layers. Normally, SPT blow are provided but you may have CPT test data. One thing that I have observed is that in alluvial sandy deposits it is quite easy to get a pile through as the increased pore water pressure during driving allows this to happen. After the soil ad freezes on the pile it becomes very difficult to move the pile if you have a problem such as a breakdown. Static Cone testing results versus SPT may be of more value for design in such deposits. The SPT may give low values but this mimic's the situation re driving in the deposit.

In the end the choice of foundation type apart from cost and liquefaction concerns is based on the loads that you need to accommodate. If you wish to use a driven pile I would have at least two testpiles driven at the site using an H and pipe pile. In my experience if the till is cobbly and deep penetration is required then the Hpile is the answer. However, I like closed end pipe piles as well but the choice depends on where you require the pile toe to be founded.

Let us see the soil characteristics and tell us wheteher liquefaction is a concern or not so that some better information if any can flow.