Apartment Building With Very Large "Seperation" Crack 4

[YuleMsee]

Did a recon visit to a building I've been asked to give an opinion on for the cause of cracking and recommend remedial measures.
Photos and a preliminary structural layout are attached. The building has ground + 3 suspended levels then a pitched roof, gravity load path is through load bearing natural stone masonry walls with some 250x250mm columns as shown. Foundations for the walls are strip foundations. Slabs are 150mm thick with 450x200mm beams.
Along gridline C there is a level change on the floor slab as indicated on the layout with a staircase and on the photos you can see different floor slab beam levels.
The crack also runs along this gridline, its visible on the exterior and interior wall surfaces, runs also on the floor slabs.
An attached sketch also shows how the land around this building is like, there is a slope on two sides of the property captured with the orange pen. one photo captures the slope as well.

I intend to bring on board a geo-tech engineer as I think the slope and the less than one year old neighboring building may have an effect. I also intend to do some reinforcement scans on the floor and beams at the crack location just to see how the step was implemented. Finally open an area to look at the size strip footings.

In your enlightened opinion, what else should I investigate

Though I have to admit the nature of the crack is giving me pause, wondering whether I'd like to be involved in this!

 

[SlideRuleEra]

I intend to bring on board a geo-tech engineer as I think the slope and the less than one year old neighboring building may have an effect.
...what else should I investigate?

IMHO, the problem is more likely to be geotechnical than structural.

1) I believe you are right, if the new 12-story build is on footings (not piling) and is relatively close (like your sketch), the new building could have effects on the problem building's foundation.

Other potential issues:

2) Seismic activity.

3) Change in ground water elevation. Change is important, not necessarily depth to groundwater. This could be from, heavy rains, drought, temporary dewatering for construction of the 12-story building, or tree roots.

4) Excessive vibration from heavy equipment during construction of the 12-story building, especially if the 12-story building is on driven piling.

 

[YuleMsee]

@SlideRuleEra

On seismic, we are in a low risk seismic region

Ground water could indeed be an issue,
The property sits at the brow of a slight hill, two sides as indicated fall about 30m in height in a steep slope 1:2.5 and the bottom is a seasonal stream
I noted the neighbour on the north end has very funny rain water drainage, puts half his water in a soak pit and the other half drained via surface runoff, couldn't access the new development to see how they handle drainage
Our region has been going thru a prolonged drought, two years of depressed rainfall

The foundations of the new development are definitely not piles, either isolated footing or a raft

The soil is non expansive clay, with a safe bearing capacity of about 100KN/m²

 

[JoshPlumSE]

One thing I don't think you mentioned is the age of construction of this building. Has it been there for 5 years, 10 years, 20 years? Also, when was this cracking first noticed?

Right now it looks like the cracking is confined to drywall. Is that correct? Does this go all the way up the building for all floors? Has any damage been noticed in the structural elements? It would be especially noticeable in concrete or masonry.

You might have to knock out some drywall to see if the structural walls aren't not visible from crawl spaces or from the outside.

 

[JoshPlumSE]

Let's say we determine it's some minor settlement from the adjacent construction or the increased soil load from that building. The question then becomes if we can expect the settlement to continue getting worse.

If we don't think it's going to get much worse, then the best bet may be assess and wait. Drywall is relatively cheap / easy to repair. Wait another couple of years to make sure all settlement is done. Make sure there isn't true structural damage, then go ahead and repair the drywall.

If the damage is in structural walls, then we might want to mitigate it somehow. Not my area of expertise, but there are methods to "jack" up building differentially at locations of excessive settlement. I don't know if this would involve injecting expansive grout, using helical piles or what.

 

[YuleMsee]

@JoshPlimSE

There is no dry wall, the wall os plastered and painted on the interior and key finish for masonry mortar joints on the exterior.
Yes, the cracks go thru beams and floor slab as seen on the third photo, the exterior wall photo

Building is 14 years old, cracking has occured within the last one year.

 

[HTURKAK]

The second picture of the first post ...My gut feeling is , the spreading and creep of the foundation soil at slope side..

My suggestion would be , lifting the settled ftgs to original level , underpinning of the foundation , improving the surface drainage conditions .. But work with an experienced GEOTECH group..









Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[gte447f]

Since the crack(s) have apparently occurred along a line where there is a sort of discontinuity in the structure (i.e., a vertical step in the elevation of the foundation and each floor slab/frame), my gut instinct would be that the cracking might likely be the result of something inherent to the original structural design or construction, because stress concentrations or risers are naturally likely to occur at such discontinuities. It could also be related to foundation settlement of course. Construction of the newer adjacent building could also have an influence, but my initial opinion would be that that would not be the most likely scenario. It sounds like you may have some money/fee to put toward this investigation. If so, and I thought settlement might be an issue, I think I would start by recommending some sort of elevation survey/mapping of each floor of the building to try to identify whether and how much movement might have occurred, and if there is a discernable pattern to any such movement.

 

[dhengr]

YuleMsee:
I would check with a GeoTech guy about the prospect of slope stability and if the sum (weight) of the two bldgs. brought this on. That is a pretty steep slope and it is very close to the bldgs. However, the vert. cracks which can be seen in your photos do not really show much relative vert. movement btwn. the two sides of the cracks; nor do they seem to show much width variation from top to bottom. I would want to monitor these cracks over time. Put some marks or gages on the cracks to monitor their movement. It also appears that there is an intended elev. change in the floor framing system at grid C. This can be seen in the ext. conc. beam elevs. on the ext. photo, your third photo, looking up the ext. wall, btwn. the two large balconies. What do the structural framing details look like in this area, on this grid line, and how could they be influencing the cracking? Is there paint or dust and crud in the cracks which would indicate that they have been there for a long time? Do similar cracks show up all along grid C? Really study these cracks for variations and changes at various details and locations and take many more photos, identified by floor and location and detail and shown on you plan, to start to hone in on any similarities and differences and what might be causing the problem.

 

[YuleMsee]

@HTURKAK

"My suggestion would be , lifting the settled ftgs to original level , underpinning of the foundation."

How do you achieve this for a strip footing?

 

[YuleMsee]

@gte447f

my gut instinct would be that the cracking might likely be the result of something inherent to the original structural design or construction, because stress concentrations or risers are naturally likely to occur at such discontinuities.
I think I would start by recommending some sort of elevation survey/mapping of each floor of the building to try to identify whether and how much movement might have occurred, and if there is a discernable pattern to any such movement.

I agree, we will propose reinforcement scans to see how construction was implemented at that point.
A movement survey would greatly help, thanks for pointing that out

 

[YuleMsee]

@dhengr


What do the structural framing details look like in this area, on this grid line, and how could they be influencing the cracking? Is there paint or dust and crud in the cracks which would indicate that they have been there for a long time? Do similar cracks show up all along grid C? Really study these cracks for variations and changes at various details and locations and take many more photos, identified by floor and location and detail and shown on you plan, to start to hone in on any similarities and differences and what might be causing the problem.

I have to investigate how the framing was done, will use reinforcement scanner.
Yes, the crack shows on the walls on gridline 1, goes thru the slab as shown on the layout and then appears again on the walls of gridline 3, its as if its forcing a movement joint on gridline C
I will have to study the cracks more keenly when and if the real work starts

 

[HTURKAK]

My initial respond would be underpinning with helical piles, micro piles or jet grouting acc. to local available technics and equipment access.

Pls look to the following doc. to get an idea .


I would like to remind you , provide more details to get better answers..










Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[YuleMsee]

@HTURKAK

I would like to remind you , provide more details to get better answers..

I just did a recon visit, so I don't have all details, if my quote is agreeable to the developer I'll have more information