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# Questions tagged [foundations]

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### Mat Footing (Bending Moment Issue of the Short Strip)

Hi I'm a civil engineering student, I wanted to ask for help and clarification for the design of mat footing. I used the Rigid method and based my design on the ACI 336_2R and Foundation Engineering ...
0 votes
0 answers
19 views

### Mass Brick Settling Causing Excess Load On Center Beam

I live in a 115+ YO building and recently had my kitchen remodelled. During this the subfloor was replaced (old 1x6s in bad shape). I noticed a significant bow in the joists with the central steel ...
0 votes
1 answer
41 views

### Shoring beams properly installed?

Question about a home my wife and are looking at purchasing. The garage had an office/apartment on the second floor, and the seller disclosed that the floor had sagged and been fixed with shoring ...
0 votes
1 answer
79 views

### Wood vs steel supports for small bridge

I'm interested in building a small access bridge across a creek on my farm. This bridge will be approximately 5m long and 3m wide and my tractor is about 4000 pounds. I read somewhere a long time ...
1 vote
3 answers
215 views

### Grade Beam vs Wooden Pile Foundation

We are in the design phase of a home at the New Jersey seashore. We are having a hard time deciding between a grade beam over pile foundation or having the home built on a regular pile foundation. The ...
1 vote
0 answers
21 views

### Do we allow mass and moment of the footing itself, when calculating ground support and eccentricity of a footing?

Suppose we are designing a footing for the wall of a building. There are two checks that are crucial. Ground support: suppose the ground is assessed as being suitable to load up to 80 kN/m2. Then a ...
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0 votes
1 answer
2k views

### Relation of shear strength to bearing strength of soil by formula

From formulas: Shear Strength: $τ = c+ σ'\cdot sin\phi$ Bearing strength such as: $1.3 cN_c+ qN_q + 0.4B_γN_γ$ Now I know that bearing capacity decreases as the shear strength of soil decreases. ...
• 462
1 vote
2 answers
53 views

### Pouring large circular footing in segments

Lets say we have a very large and deep circular footing for a tall tower such as an industrial chimney or a wind turbine, and for convenience we want to pour it not at once but in sections. Can this ...
• 462
0 votes
3 answers
147 views

### How to make top of rebar cage of CIP pile exposed

A long time ago I saw that when cast in place piles were poured, the rebar cage was lowered all the way to the hole and the concrete was cast. After the concrete hardened, the soil around the top of ...
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1 vote
1 answer
211 views

### PE exam: situations in which two question choices are close to my final answer: how to pick one?

Consider this question: I solve this eventual question and my answer is 7.29667: Among the question choices are 7 x 7 ft and <...
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2 votes
2 answers
38 views

### Small building basement foundation moisture: permeable vs impermeable

I understand that moisture is the enemy of interiors. I know that the standard basement foundation for a house-sized building uses moisture barriers on the outside of concrete retaining walls to ...
4 votes
2 answers
9k views

### What does "crs" mean in structural engineering / construction?

In the realm of structural engineering, construction, foundation design, what is "crs" when talking about piles/posts? Is it an abbreviation? Does it refer to some sort of size? Some ...
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0 votes
1 answer
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### How do extra building levels affect the foundation design apart for the extra load?

I have been talking to some structural engineers trying to find one to design foundations for my contemplated bespoke building based on hi-cube 40-ft shipping containers. The initial concept is just ...
• 211
0 votes
1 answer
146 views

### Distance of raft foundation outwards

Can you tell me (for USA) which code (or standard or guide) and in it where exactly I can see the distance required for the raft foundation, as far as how much it should extend horizontally beyond the ...
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3 votes
3 answers
93 views

### Low pile capacity during pile driving

When driving piles, the resistance from the soil is constantly measured. What happens when the expected resistance values from the soil are not obtained? For a single pile or for multiple piles? What ...
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1 vote
1 answer
344 views

### Effect of overburden pressure on the skin friction pile capacity

In a given soil, the lateral effect of overburden pressure is constant with depth, as in $p=qk$, where: $p$: lateral pressure effect, $q$: overburden pressure $k$: soil lateral pressure coefficient. ...
• 462
2 votes
2 answers
1k views

### Why is the wet/dry boundary of ground not dangerous for foundations?

A building, such as a house, rests on a foundation. Beneath it is natural earth. When it rains, the ground around the foundation becomes wet. But the ground underneath the foundation does not. There ...
• 507
3 votes
2 answers
452 views

### Concept design for an extension to a blanket raft slab

A blanket raft is a type of solid slab raft consisting of deeper ‘toe’ sections running around the edge of the foundation as well as a central deeper ‘beam-like’ section which offer rigidity to the ...
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0 votes
1 answer
33 views

### 18' header beam installation for single story room addition

Im expanding my 28' wide single story composite shingle home. I want to come out perpendicular off 1 plane of the roof to expand master bedroom, and then remove the wall. The foundation is crawl ...
0 votes
1 answer
68 views

### Capacity of plain concrete foundation on grade [Civil UK]

A client has asked whether a container can be placed on an existing unreinforced concrete foundation of depth 100 mm. The grade of the concrete is unknown. How can the capacity (in kPa) of this plane ...
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1 vote
1 answer
8k views

### At what level is the Grade Beam most effective at pile cap level or at Slab-on-grade level?

The primary two functions of a Grade/Tie Beam in spread footing and/or pile caps foundation system is to support the Slab-On-Grade (S.O.G) and/or to take the moment from eccentric footing (or moment ...
• 503
0 votes
2 answers
2k views

### Difference between Allowable Bearing capacity Service and Ultimate?

When we calculate the dimension of a foundation we always use the allowable SERVICE bearing capacity (lets call it qs) and all the necessary checks are based on this value qs. My question is why does ...
• 503
0 votes
1 answer
320 views

### 3 x 1 stone under footing and sump crock

I am having a house built and the builder found organic soils during the excavation. They removed the soils and then filled the cavity with 1x3 stone (see picture). This is the corner where the sump ...
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19 votes
3 answers
4k views

### What is the purpose of building foundations?

According to many sources, one of the purposes of building's foundations is "To distribute the weight of the structure over large area so as to avoid over-loading of the soil beneath." (Wikipedia) On ...
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-1 votes
1 answer
48 views

### International Building Code vs Industry Standards

Which is more reliable. For example, in setting steel posts in the ground, the pole should go under ground 1/3 of its height from the surface up. In IBC, steel post depth is made rather on a storey ...
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0 votes
1 answer
706 views

### using air pressure as a liquid pump

I have a $100\ \text{psi}, 300\ \text{cfm}$ air compressor that we use for running power tools, I need a way to inject mortar deep into a small opening and was wondering if anyone had experience with ...
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8 votes
1 answer
836 views

### Why is this construction site pouring gravel over a wire mesh, and then covering it with dirt?

My office is afforded a prime view of a construction project where the workers are currently covering the leveled ground in a wire mesh, raking gravel across the entire mesh, and then covering that ...
• 187
1 vote
0 answers
851 views

### Shift Concrete Column by few inches

While building the foundation of a house, the concrete columns were built 15cm (6 inches) from the planned position, which is reducing the space for a door. The position that should have been there ...
• 111
2 votes
0 answers
55 views

### Affect of Cast in Pipes in a 1m thick Raft Slab on shear

I am designing a 1m thick raft slab and the drainage guys have thrown in 100mm diameter cast in pipes all over the raft. See Attached images 1 & 2. Wondering how this will affect the shear in the ...
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4 votes
2 answers
4k views

### Bored Pile construction Procedures When having Water in the ground

I know the normal process of how bored piles are normally constructed, but I need to know in case we have a water table at 1.5 m under the surface level and the pile must be at a depth of 25 m. How do ...
• 503
3 votes
3 answers
5k views

### Building Uplift due to water pressure

I have a building that is 7 story height (which 5 stories are basement floors which means they are underground) My water level is at 1.5 m from the surface. the stories have typical rectangular shape ...
• 503
6 votes
3 answers
2k views

### For train track, why does the ballast need "good drainage"?

Why does the ballast of train track need good drainage? I read something about preventing "fouling" of the ballast, but don't know what that means or why it would be structurally bad. Could ...
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3 votes
0 answers
154 views

### Can shear links be designed to hook between inner layers of top and bottom reinforcement?

I am tasked to design a bridge pile cap. Shear links are required. However due to heavy reinforcement used, contractor requested to hook the links between inner rebars to ease construction. Is this ...
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3 votes
1 answer
30k views

### why are foundations designed at SLS

Why do we design foundations at SLS and not ULS? If we use ULS wouldn't we be taking a higher factor of safety? SLS = Serviceability limit state. It considers how the structure is actually expected ...
• 180
4 votes
1 answer
673 views

### Foundation Excavation: How much larger than the RCC footing?

I am trying to estimate the volume of excavation needed for the foundations of a structure from the drawings provided. The drawings clearly give the dimensions of the RC / cement footing but I ...
• 422
6 votes
2 answers
7k views

### What is the down-stand beam called at an edge of a surface bed or raft foundation?

What is the down-stand beam called at an edge of a surface bed or raft foundation? It is not exactly a grade beam or stem wall. It is more like a toe.
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4 votes
2 answers
2k views

### How to model elastic support in FEM?

I need a 8 m x 4 m x 0.6 m RC plinth (mechanical requirement) which needs to be built onto loose gravel. Obviously I am going to over excavate, back fill with selected material and bed my plinth on ...
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2 votes
1 answer
723 views

### How is drilled shaft lateral resistance calculated using LPile?

The AASHTO LRFD Bridge Specification, Section 10.5.3.3 says "shaft lateral resistance" should be checked at the strength limit state (i.e. factored loads). How is shaft lateral resistance determined ...
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4 votes
1 answer
5k views

### Stress Bulbs for strip "continuous" footings [closed]

How can I plot such a graph with Excel or Matlab by a uniform load q, and how can I see where the stress becomes 0.1q? The loaded area and the equation is on the picture shown below, equation is ...
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31 votes
4 answers
11k views

### Why dig out and then fill in before building a large structure?

I work in the middle of London, in an area full of large office blocks. Across the road from my office they have started construction of a large building (10 stories plus). Over the last few weeks, ...
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