Preloading Near Existing Building
Preloading Near Existing Building
(OP)
I am designing a single family house which requires preloading. The ground is 6m peat folowed by 10m very soft silty clayey deposits. The property line is 1.5m from an existing new building founded on timber piles. Embankment fill toe starts from the property line. How can one calculate the maximum fill thickness in the first stage to avoid damage to the neighbouring building.





RE: Preloading Near Existing Building
Aside from that, I cannot see how preloading would negatively affect the adjacent structure, since it is on piling, unless there is an existing retaining wall involved.
Mike McCann
MMC Engineering
RE: Preloading Near Existing Building
Preloading takes a long time, and I have never known it to be used for a house. It is not a good site, and probably deserves piles.
RE: Preloading Near Existing Building
(Just to differ somewhat from MSquared48 and fellow Hokie.)
f-d
¡papá gordo ain't no madre flaca!
RE: Preloading Near Existing Building
The existing building is only 1.75 m from the toe of the proposed embankment. Total fill+preload thickness would be about 2.5m.
RE: Preloading Near Existing Building
In addition, the downdrag of the piles due to the settlement will be an issue, and probably not one that you can estimate/evaluate without knowing all the details of the piles and adjacent soil profile.
All in all, I don't think preloading is a viable option. I think you need to look at piles.
RE: Preloading Near Existing Building
"The house will be founded on timber piles. But the site need to be filled about 1.5m (+settlement) for other reasons. I presume I can call it preloading for engineering assessment of the nearby building. After reaching the design grade, only the areas on the driveways will be preloaded to about 0.7m loose materials.
The existing building is only 1.75 m from the toe of the proposed embankment. Total fill+preload thickness would be about 2.5m".
RE: Preloading Near Existing Building
f-d
¡papá gordo ain't no madre flaca!
RE: Preloading Near Existing Building
RE: Preloading Near Existing Building
RE: Preloading Near Existing Building
In other areas the filling result may be cause for a law suit.
And yes, for the idea of preluding a site for a house, I've done it numerous times with success.
RE: Preloading Near Existing Building
Settlement of adjacent property. Likely at the edges - and neighbour's land could settle a bit. (noted already)
Secondary consolidation of peat is important to consider as well as the soft clay. (noted earlier)
Lateral effect of fill on neighbour's house piling. possibility that hasn't yet been mentioned. There is a paper out there I remember seeing a while back that discusses embankment fill adjacent to a pile and its lateral effects.
Oldestguy makes a good point on the legal ramifications. The neighbours property, given the geology, might already have a few problems that have developed. You surely want to know what the base-line condition is and be able to monitor the during preloading condition.
You might consider using wick drains and perhaps get by with a smaller preload thickness for the same amount of loading time to produce the same expected consolidation settlement.
Preloading the Richmond and Burnaby Peat areas are normal practice from my recollection - likely many not even "engineered".
If I can, a case history I am aware of - Burnaby Lake Peat. 25 ft (8 m)of peat over 25 ft (8 m) soft clay then compact sand. Structure put on piles with tips driven into the sand - floor level about 2 m above ground surface. Filled up to reach the floor level (so trucks could drive into the maintenance garage)- would tend to dismiss that the site had been preloaded to any extent. Out the back, piles had been installed for later extension. Over the years, they had to cut off the tops of the "future addition" piles as the groud was settling and hampering the mainteance bay's exit. We investigated and found that they had "topped up" the entrance ramp some 4 or 5 times over the years. We decided to cut out the access ramp (sand and gravel at roughly 130 pcf) and replace it with Elastizell (at 30 pcf unit weight). The earlier gravel ramps basically preloaded the site as the net reduction of pressure was large. Went back 2 years later - no additional movement. I have a copy in storage of the old 1960s report by Fenco to the City of Burnaby on building on the lake peat.
RE: Preloading Near Existing Building
The porepressure vs clay strength should be cheked and the effect of the reduced effective stress in the peat should be checked.
RE: Preloading Near Existing Building
RE: Preloading Near Existing Building
possibly with inclinometers or pressuremeters at the property line. Lateral concerns me a bit.
RE: Preloading Near Existing Building
I have also a quastion that why the pwp increases. The water level is almose at ground level and the top 6m of ground is peat. I guess the k of peat should be high enough to prevent any pore water pressure buildup. Please advise.
RE: Preloading Near Existing Building
RE: Preloading Near Existing Building
As for drag down force, it is typically due to skin friction in the upperportion of the pile. For the peats and soft organics, I would not expect these to be large numbers. Down drag is more of a structural issue than a settelment issue.
Lateral capacity can be checked assuming at least a pinned end and sufficent lateral resitance of the pile cap.