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Steel Screw Pile Foundation

Jim Houlette — Thu, 19 Jan 2012 21:00:31 +0000

A deep foundation system that is gaining popularity in areas with difficult soil, contaminated soil and due to its speed of construction is steel screw piles.

At first glance screw piles look like the typical helical pier. However, there are significant differences that make a dramatic change in capacity. First, the screw piles are installed as a single continuous piece in lieu of sections bolted together. Second, the machinery used to install screw piles is larger and capable of producing a higher torque.

The components of a screw pile are simple; a steel shaft, steel helix at bottom of shaft, and a connection plate at the top of the shaft. Screw piles can vary in size to accommodate different design loads. The steel shaft size is a function of axial load, torsion during installation and thickness due to corrosion. The helix is a plate that is shaped just like the threads of a wood screw and engages the soil to distribute the axial load and it locks into place to provide tensile loads as well.

One of the first questions people have is, “How long will it last until failure from corrosion?” There are several factors that go into corrosion of steel; oxygen, moisture, dissolved salts and other corrosive chemicals. Since there is very little oxygen in the soil, corrosion is limited and can be controlled by using thicker material to allow for expected corrosion. The life of steel screw piles can be 50 years to an indefinite period depending on the type of structure and life span needed.

I designed foundations in Stapleton where the site was located over the old terminal and contaminated soil was discovered. If typical straight shaft drilled piers were used the spoils from drilling the hole would have had to been bagged and disposed of properly. To avoid bringing contaminated soil up to the surface steel screw piles were used.

I list a lot of PROS below and for good reason. I have been very impressed with screw piles and the wide range of uses of them. EVstudio was recently visited by Alpine Site Services for a lunch and learn. Mike Oliveira discussed how screw piles are installed and the many advantages to their system over other typical foundation types. What really impressed me was the speed of placement of screw piles. Alpine can place 30 to 50 screw piles in one day!

Another great advantage to screw piles is that they can be placed at an angle to provide bracing and tension resistance that is aligned with the force of the tension. An example is a typical counterfort that braces a foundation wall. You can see the angled screw pile above.

PROS
Fast Installation
Can be Proof Tested
Negligible Uplift Pressure from Swelling Soil
High Capacity up to 500kips
High Tensile Resistance
Made from a reusable material (LEED point)

CONS
Specialized System
Large Equipment
Concerns with Corrosion

Learn more about different foundation types.

Originally posted 2009-10-10 00:21:43.

Q&A

evstudio — Thu, 19 Jan 2012 21:00:14 +0000

One of our primary goals in writing the EVstudio blog is to answer your questions about EVstudio and your larger questions about architecture, planning, development, construction, new urbanism, real estate, Denver issues, Colorado issues, AIA issues etc. Please let us know any questions or issues that you'd like to see addressed on this website and we'll turn around answers ASAP.

Looking forward to your input. Thanks

Originally posted 2008-06-01 21:41:36.

New Website Coming

Links from EVstudio.info to Your Website

Sean O'Hara — Thu, 19 Jan 2012 21:00:04 +0000

With the increasing number of link requests that we get from Consultants, Clients, Engineers, Contractors and Builders, I thought it would be useful to explain how to get EVstudio.info to link to your website.

First, an important distinction, generally speaking our evstudio.us domain does not provide links unless we have an interest in the company. Most of our linking comes through evstudio.info which actually has higher page rank anyway.

What we have devised as the most fair way to distribute links is that we provide links within posts where describe projects. That way if we're only working on one project with a certain company we are providing less links that if we are working on five projects with another company. Just let us know that you'd like to be mentioned in conjunction with projects and we'll make sure that we do. The blog currently has a page rank of 5, so we can really help out.

The other way is we provide links to organizations and blogs that our readers may find interesting, just email me and I'll look over your site.

We always appreciate any reciprocal links as it helps more people find us and the information that we have generated to let them know more about architecture and the architectural process.

Originally posted 2009-04-16 00:46:42.

Straight Shaft Drilled Concrete Pier Foundation

Jim Houlette — Thu, 19 Jan 2012 20:59:49 +0000

When the soil is unstable and does not allow for a typical spread footing foundation a deep foundation that bears on stable soil below is needed. A deep foundation supports the structure by bearing on stable soil below the unstable soil. It may be helpful to think of a house above water supported by columns. The water represents the unstable soil and the columns bypass the water and bear on the stable soil below the water. Some of the earliest deep foundations were built the same way. The Aztecs built walkways over water by hammering logs into the bottom of the lake bed. This is a typical driven pile foundation, but the same principal applies.

There are many different types of deep foundations. In this post I will focus on Straight Shaft Drilled Concrete Piers. But other deep foundation systems include, wood or steel piles, helical piers, caissons and screw piles.

Straight Shaft Drilled Concrete Piers are constructed by drilling a hole into the ground and filling it with concrete and reinforcing. The diameter of the pier varies depending on the load the pier must support. A 10” to 12” diameter is typical for light loads in residential. Typically, a pump truck with a long tube is used to place the concrete directly at the bottom of the hole to displace any water.

The reinforcing is needed to provide a tensile strength for the pier to resist uplift and moment forces. For small residential piers three to four vertical bars are placed the entire length of the pier. As the loads become larger, a cage of steel may be needed in addition to the full length vertical bars.

Drilled concrete piers must be designed to support the applied loads from the structure and the forces from the unstable soil. First, the applied load from the structure is transferred into the pier and the load is distributed into the bearing soil through skin friction and end bearing. With unstable swelling soil an uplift force may be applied to the pier as the soil swells pushing in on the pier. I like to describe this action similar to the water snake or water tube toys. When you squeeze the toy it slips out of your hand. Obviously, concrete doesn’t behave like water, but when the soil pushes in on the concrete pier the soil pushes to concrete pier up and out of the ground. So the pier must extend deep enough into stable soil to resist this force, therefore, creating a tensile force between the stable and unstable soil layers.

The design of deep foundations can get very complex and the design allows for very little forgiveness if done incorrectly. Unfortunately, this has caused many geotechnical and structural engineers to over-engineer drilled piers.

PROS
Minimal labor
Bypasses unstable soil

CONS
Expensive
Subject to failure if incorrectly designed
Does not address basement floor, so an elevated structural floor is typically needed

Learn more about different types of foundations

Originally posted 2009-10-03 00:01:44.

Quickly Construct Concrete Pad Footings with FASTBAG

Adam Denton — Thu, 19 Jan 2012 20:59:39 +0000

At a recent seminar I attended I was introduced to the Fab-Form product called FASTBAG. This product is brilliantly simple….a textile bag you can fill with concrete and reinforcing bars to take the place of the wood formwork traditionally utilized to construct pad footings.

FASTBAG in the field.

The bags come in multiple sizes designed to replace standard pad footing sizes. While the shape of the filled bag does not look like the traditional footing the contact patch and load path are designed to be identical to a square footing as illustrated below.

I admit I have not seen these bags used in practice and unless I come across a project that requires the use of multiple pad footings I am not certain they would pay off over traditional wood forms for new construction. However, I do a lot of retrofit structural design for residential repairs and remodels and I see that the FASTBAG would have a wonderful application in this arena. I have had many projects that require new concrete pad footings to be constructed in very close quarters such as crawlspaces. I can see this product being a considerable help to a contractor who needs to construct a footing deep inside a crawlspace with only 20” of clear space to maneuver in. Stay tuned to this blog for a follow up report on the real world application of this product.

Originally posted 2011-03-31 00:21:24.

Spread Footing Foundation

Jim Houlette — Mon, 12 Dec 2011 23:46:24 +0000

This has to be the most typical foundation type with basement or crawlspace construction. The spread footing design is simple; provide sufficient footing area to distribute the weight of the structure onto the soil. Typically, a 16” wide x 8” concrete footing is used.

The width of the footing distributes the dead and live load of the structure on the soil allowing a typical 8” wide concrete wall to be placed on the footing in lieu of a wide 12” to 16” concrete wall. In addition, the poured footing helps to provide a level surface for the concrete foundation walls. The thickness of the footing will vary due to unlevel soil conditions. The designer should also keep in mind that even if a 12” wide footing satisfies soil bearing, the foundation crew may need at least 16” to allow enough area to set the wall forms on the footings and allow for dimension errors to be adjusted.

A typical spread footing foundation is also referred to as a ‘T wall’.

PROS
Cost effective
Common Construction
Low Tech

CONS
Fails with Swelling Soil

Learn more about different types of foundations

Originally posted 2009-09-13 02:09:33.

Building Season in Colorado, What About Winter?

Sean O'Hara — Mon, 12 Dec 2011 23:46:23 +0000

We frequently have projects and clients who are concerned with the idea of building during a Colorado winter. Snow, ice, cold temperatures and frozen ground can all make building more difficult. With that being said, in the Front Range cities, like the Denver metro, we can generally build year round without many weather delays. As you get into the mountains the delays become more frequent and if you have the luxury of picking your time for building it certainly makes sense to work around the winter.

There are techniques for doing work with frozen ground and cold temperatures, you can tent, you can change your concrete mixtures, you can use blankets to thaw frozen ground, but they do have cost premiums. At the same time, the price of waiting for the spring can also add cost to a project.

Of course the other thing that we all know about the weather in Colorado is that its always changing and hard to predict. You can have a December where the snow doesn't melt, or a March with no snow or a May where it rains almost every day. In any schedule you should plan for weather delays but you shouldn't let the winter be the deciding factor in when you build in Colorado.

Originally posted 2011-05-29 00:27:29.

Separation of Top of Foundation Wall and Adjacent Exterior Grade

Adam Denton — Fri, 09 Dec 2011 23:50:08 +0000

One of the most commonly asked questions to the structural department involved the required distance between the top of a foundation wall and the adjacent exterior grade. The 2009 International Residential Code requires a minimum of 6 inches of separation where brick veneer is not present. The idea here is to provide a buffer zone to help prevent moisture wicking into the timber framing typically framed above residential foundations. Where brick veneer is present this requirement drops down to 4 inches.

The code text reads:

R404.1.6 Height above finished grade. Concrete and masonry foundation walls shall extend above the finished grade adjacent to the foundation at all points a minimum of 4 inches (102 mm) where masonry veneer is used and a minimum of 6 inches (152 mm) elsewhere.

An example of where minimum separation is close, but not met.

Originally posted 2011-04-03 00:01:32.

Landscape Architecture available from EVstudio in Colorado

evstudio — Fri, 09 Dec 2011 23:50:05 +0000

Landscape Architecture is a necessary component for land development plan approval and building permit approval for many jurisdictions. EV Studio provides landscape architecture along with all other related disciplines to assure quality control for your project.

We work with a broad range of private and public clients on project types including detached and attached single family housing, multi-family housing, schools, offices, medical, and retail spaces. Our services include streetscapes, parks and recreation, land entitlements, design guidelines and even HOA retrofits. We practice sustainability with all of our landscapes selecting appropriate plant material for the context and working closely with our civil engineers to manage and utilize storm water effectively. We offer full service landscape architecture including necessary construction documentation and specifications.

Our Director of Landscape Architecture is John Olson, RLA, LEED-AP, CNU-A. John has over eight years of landscape architecture experience and has worked on projects in a variety of climates across the country. John will be your landscape architecture point person on your project. Some of his recent work includes landscape architecture improvements at Medinah Country Club (home of the 2012 Ryder Cup), the Pueblo Justice Center in downtown Pueblo and planning and entitlements work for The Mountain Preserve, a luxurious sustainable development south of the Broadmoor Hotel of Colorado Springs, owned by famous folk singer Pat Boone.

Originally posted 2010-05-07 00:01:22.

Foundation Settlement: The Push Pier Alternative

Adam Denton — Mon, 21 Nov 2011 08:02:26 +0000

EVstudio is asked quite frequently to perform structural evaluations of cracked foundation walls. These cracks are often due to settlement. Modern design philosophy (and most geotechnical reports) calls for the original structural engineer to design foundation walls to clear span ten to fifteen feet to account for soft patches of bearing soil or soils that may be become saturated and hydro-consolidate (shrink in volume when wet). Older homes are more susceptible to damage because they were typically not designed with this in mind. This is not to say they were designed poorly, there were just different design philosophies and industry standards at the time they were constructed.

There are many different ways to approach the problem of foundation settlement. One way is the foundation push pier.

Steel push pier with hydraulic ram installed.

How a push pier works is quite simple. First, a steel bracket is fastened to your foundation, typically at the footing. Then a hydraulic ram is installed on the bracket which pushes a steel pier into the ground. Using the hydraulic forces in combination with the weight of the structure above, the steel pier is driven down through the softer soils (which are causing the settlement problem) until bedrock or suitably firm soils are reached. Once the pier reaches competent bearing, the foundation is stabilized and in some instances can even be raised back into a level position.

EVstudio works closely with foundation repair contractors such as Pinnacle Structural Services in the evaluation of foundation repairs utilizing the push piers as one of many considered solutions.

Originally posted 2010-06-26 00:01:29.