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The steel support for timber wood retaining wall on a forest slope in Westmount, London, Ontario, 2022

Timber wood retaining wall supported by sophisticated steel structure in environmentally sensitive area. JW Portable Welding & Repairs, Westmount area in London, 2022

The steel support for the timber wood retaining wall built on a slope of Westmount in London, Ontario was, without any doubt, the most sophisticated project of 2022 for JW Portable Welding & Repairs. Many crucial aspects have affected the sophistication of this project. Among them were: environmental impact along with difficult access, and technological impact along with complicated joints with large gaps and large welds, extremely precise manual cuts on large structural steel and variety of size restrictions that were difficult to predict in advance. I realize that many construction professionals looking at this timber wood retaining wall on a slope will accuse me of exaggeration. They will simply not see these challenges. However, please restrain your judgement until the end of this article.

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Impact of environment when building wood retaining wall on a slope

When we talk about environmental impact on a wood retaining wall we should consider weather (rain), slope and access to the slope, soil type and the depth of “untouched soil”, and presence of trees and tree species type. These factors will impact not only the technology used but also technical construction aspects as well as a project’s budget.

Weather impact on building a retaining wall

The slope always complicates building any retaining wall, but timber retaining wall provides an attractive easy to built and relatively inexpensive solution. We use these these type of retaining walls to cover long distances and they provide excellent carrying load at relatively low cost. They not only stabilize the soil movement on slopes protecting the structures above the wall but also can be constructed in difficult slope conditions.

In our Canadian climate the construction should start in early summer. When is already relatively dry and fairly warm is the best time to begin construction. In this way we avoid slippery conditions on the slope that will affect not only workers but also equipment used. Certainly, digging holes for the soldiers, the steel columns, visible on images below won’t be easy on high slopes during rainy day.

Rain is probably the most detrimental factor from all weather components since it can cause havoc during construction, and increases the risk of land slide on the slope. Also, rain contributes to specific hazards in welding processes such as potential electrocution and porosity of welds.

Slope affects construction of retaining wall

The slope affects not only material used, but also how the construction of the retaining wall will progress. And it affects the equipment used. In my opinion, the slope affects also the most important factor which is the load carrying capability of retaining wall. Moreover, the location of slope in comparison to the retaining wall location is paramount.

In many instances, the location of retaining wall is beyond our control. Therefore the slope affects the retaining wall in front of the wall as well as behind the wall. The slope in front of the wall will dictate the load carrying capability since it will directly affect the mass of soil that retaining wall will have to support. And the slope behind the wall will dictate how we will build the wall, material used and equipment used during construction. The slope behind the wall also affects the access of equipment to the construction site if the access from the road above is not available.

As much as timber wood retaining wall provides rather relatively inexpensive solution to the land sliding problem, the steel soldiers are rather necessary at higher slopes even if they increase the project’s cost. The steel soldiers not only increase carrying load of a retaining wall but more importantly provide options to increase the carrying load even more by attaching steel structural support to the steel soldiers. Therefore, using steel soldiers in timber wood retaining wall that is going to be built on the slope reduces significantly the risk of retaining wall collapse and failure. If you suspect that your timber wood retaining wall is leaning call us.

Water retention causes failure of retaining wall on a slope

Many homeowners and property managers wander why their retaining wall cracks and then fails. The answer is relatively simple. Their retaining wall has failed since the mass of soil have exceeded the retaining wall’s carrying load. These type of damages usually appear in spring and after very long rains. The soils that retain water very well suddenly increase their mass and then the particles of soil looses friction and slides pushing on the retaining wall. Because the soil is usually not the same in front of the wall that is why parts of the wall that face soil that retain water more are at higher risk of failure.

It is very difficult to precisely establish what kind of soil is in front of the retaining wall. Patches of different soil laying at different depths, could have different water retention and they will impact the retaining wall differently. Therefore monitoring of retaining wall on a slope is very important.

Degree of slope

The degree of slope affects also the equipment used during construction of the retaining wall and consequently impacts certain technical parameters and construction tasks. If you consider that all heavy equipment that provides relatively precise drilling of large diameter holes in soil does not operate well on high slopes then the window of options will narrow to a light drilling equipment. Unfortunately, the light drilling equipment drills holes in soil less precisely on slopes even if operated by very skillful operators. Also, the light drilling equipment has difficulties reaching required depths or sometimes drilling bigger diameter holes. These weaknesses of small drilling equipment will affect the straightness of the retaining wall and will complicate the installation of additional steel support.

Depth of holes

Many professional engineers used term “undisturbed” soil and many require independent inspection confirming reaching the undisturbed soil level. However, anybody who ever dealt with physical attributes of soil knows that undisturbed soil level is difficult to confirm by drilling the hole for the soldier. The old fashion way was to dig the large hole by hand or by equipment and then physically checking the properties of soil in different levels including colour, participation of rocks and their sizes / composites, participation of organic elements, soil level hardness’s. Now we very rarely use this method.

From other side, the modern method involves taking samples from certain depths in the ground, but is expensive and difficult to do on the slopes. Taking sample process would have to involve participation of heavy equipment that has difficulties moving on slopes. Consequently, the participation of heavy equipment will increase the cost of the project and in majority of the retaining walls built on a slopes is not practical.

Enginneer describes the depth of holes as reaching undisturbed soil and expectations to reach bedrock are rather slim the presence of steel soldiers is paramount and additional structural support using heavy steel elements provides a solution to retaining walls under the risk of failure.

Presence of trees impacts the soil and construction of retaining wall

Presence of trees impacts the construction of the retaining wall very significantly. From the construction of timber wood retaining wall point of view that is built on a slope, trees play positive and negative roles. Obviously, trees play a positive role in stabilizing the soil in front of the retaining wall. In this aspect, however, we have to differentiate between species developing more spread and wide root systems from species developing more vertical root system. From the point of soil stabilization the species that develop more spread root system are more beneficial although their benefits depend on the type of soil too.

The approval to remove trees for the purpose of building a retaining wall could become a time and costly task. And the whole process depends on municipality. Therefore we should construct the retaining wall in such a way that will avoid trees in its path.

However, the roots of these trees also play a negative role in construction of timber retaining wall. The presence of large roots on the surface makes movement of light drilling equipment difficult. The presence of large roots in space where we are going to drill holes makes the location of holes less precise. Moreover, large roots combined with heavy rocks can damage the drilling components of light equipment.

Technological challenges erecting supporting structure from steel for timber retaining wall

Once the timber wood retaining wall is finished it is a very good idea to monitor the behavior of steel soldiers for leaning out of vertical position. Such dislocation of steel soldiers will signalize that the retaining wall needs a supportive system made from heavy structural steel to increase the carrying load capacity.

In fact, this is the moment when JW Portable Welding & Repairs was contacted to erect the supporting structure for timber wood retaining wall on slopes in Westmount in London, Ontario.

The steel structure erected from HSS that will support steel soldiers within the timber retaining wall will have to accommodate the huge  tree stomp close to the wall.
Our steel support will be attached to steel soldiers / columns marked 9, 10, 11, 12 and it will have to accommodate this huge stomp left after cutting the large tree. The terrain is similar to forest ground on the slope and movement of light drilling equipment will face challenges. JW Portable Welding, London, Ontario, 2022

Realizing that November is not the best month to gear up for such sophisticated project, we have decided to postpone the project to the spring of 2022. However, we have taken reading of soldier’s positions in reference to other soldiers in November of 2021. In the attempt estimate the movement of the soldiers, we have taken the same reading in late March of 2022 and then compare them both. In conclusion we have discovered that soldiers have moved in some areas of the retaining wall as much as 1″- 3/4 as measured at the top of the soldier. We have not expected this reading.

First step – welding horizontally positioned HSS’s to join soldiers together

As a matter of fact, welding of horizontally positioned HSS, 6″ x 6″ x 3/8, shouldn’t be a problem but the joints between HSS’s and soldiers have developed gaps due to movement of soldiers, and unprecise soldier locations. Definitely the environmental factors such as weather, slope, and presence of trees have played the role here. These gaps have ranged from 3/16 to even 3/4 of an inch. Considering the required size of weld of 5/16 of an inch and the gaps ranging from 3/16 to 3/4, the final weld size should range from 1/2 of an inch to even 1″-1/16. At this moment we have realized that we have a serious welding project in our hands.

Making large welds in flat position does not provide any challenge to experienced welder, but making large overhead welds of the size between 15/16 and 1″ -16 could be challenging especially if we wanted to increase the size of each weld by 1/16 in order to avoid any mistakes. Additionally, we had to generate thes large welds between two HSS’s on the same soldier. Therefore, we had to establish the minimal distance between HSS’s on the same soldier in order to make enough space for welder’s hands and enough space for our tooling. We have established the minimum distance between horizontal elements on one soldier at 8″.

The minimum distance between horizontal elements was established at 8" due to   necessary access for welder to generate  large overhead weld and access for our tools. The distance is marked with blue arrow. JW Portable Welding, London, Ontario, 2022
Minimum distance between horizontal elements marked with blue arrow. JW Portable Welding, London, Ontario, 2022

First challenges

As simple as it sounds, the planning to position the HSS’s horizontally while maintaining the minimum distances between HSS’s on the same soldier and placement of HSS at designated height wasn’t easy. The slope degree was interfering with either the HSS designated height or maintaining the minimal distance between HSS on the same soldier. I remember frustration building up, but finally at third approach we knew how to position these HSS elements.

Placement of wedges to cover the gaps

In order to cover these large gaps and still provide a good quality weld, we had to install/weld in wedges. Since the soldier’s flange was 5″ wide and HSS was 6″ x 6″ these wedges were made in 5″ x 6″ with thickness of the wedge depending of the gap between the soldier and the HSS. Additionally, we have installed heat shields to preheat the wedges in initial welding. Not to mention, that we had to install heat shields during the welding process on each soldier.

Horizontal elements are finished

It took as a few days to weld the horizontal elements to the soldiers. Obviously, according to our policy, we have sent pictures of all generated welds to the engineering firm Roar Engineering in Mississauga and to our general contractor PuroClean. I would like to use this occasion to express my gratitude to Roar Engineering for its support resolving issues without delays and to PuroClean for being patient and understanding.

All horizontal structural elements are welded to steel soldiers. In this way all soldiers are joined together. Getting the layout right was a difficult task. JW Portable Welding, London, Ontario, 2022
All horizontal structural elements are welded to steel soldiers. In this way all soldiers are joined together. Getting the layout right was a difficult task. JW Portable Welding, London, Ontario, 2022

Step 2. Drilling the holes, concrete pouring, and installation of base plates

The location of base plates in reference to the soldiers was crucial to increase the diagonal support for the soldiers therefore they had to be placed perpendicular to the flange of the soldier. Moreover, the distance of the base plate from the soldier should’ve been equal to the height of designated horizontal HSS. In this way, the supporting diagonal element will be placed at 45 degrees to the soldier. And such position would have been optimal for maximum load support

Obviously, we had precisely established drilling points but understandably we knew that such precise position of base plates would simply be impossible due to very difficult environmental factors. Additionally, during the planning stage, it has become obvious that we will not be able to drill holes exactly at the planned distance due to variety of obstacles. These obstacles included close proximity of large root systems or very steep slope. Especially, very steep slope was making positioning of light drilling equipment simply impossible.

We knew mistakes going to happen due to tough forest terrain

Therefore we knew back then that we can do the best we can but we will not be able to achieve the ideal placement parameters for out base plates. I would like to also mention that all our base plates were placed horizontally with high degree of precision. The plate sizes were 8″x 8″ and they were embedded in concrete by using 12″ long, 7/8 galvanized foundation lag bolts. Considering best trade practices, there wasn’t much space to weld our 4″x 4″ diagonal HSS elements. Looking back, we should have made 10″ x 10″ base plates that would provide more placement flexibility.

Step 3. diagonal elements

As per engineered drawing we should’ve use HSS 4″ x 4″ x 3/8 for diagonal elements. And we wanted to make sure that there won’t be any gaps between the cut diagonal HSS and horizontally placed HSS or horizontally placed plate. We knew that placement of wedges is not an option due to placement difficulties and due to best practice recommendation for welding wedges.

Additionally, we had found that all our angles vary from 45 degrees on both ends of the diagonal element and both ends should contain composite angles due to unprecise placement of base plates. Our base plates when placed in the concrete of the center of the sono tube formed angles ranging from 78 degrees to 87 degrees to the soldier’s flange causing the necessity of cutting composite angles.

Moreover, we were planning to put the bottom wall of the diagonal element slightly above the bottom wall of the horizontal element. Such position is the most comfortable for the welder to make large overhead welds since no root pass is necessary. However such placement would require extremally precise cuts to the length of the element and to the composite angles on both sides of the element. Certainly, such cuts are possible on laser cutting equipment but such task requires precise CAD/CAM drawings of each element and then each end of the element would have to be separately programmed. We knew we had to do it by hand but how?

Making wooden templates

We have decided to create wooden template for each diagonal element. Following our plan we have spent a couple of days on site building the templates. First, we have marked each location and then we have used a miter saw to create very precise wooden templates. The process not only involved the composite angles on both sides which is relatively easy using a miter saw, but also each template had a proper length.

Therefore through multiple tryouts we finally got our diagonal elements made from wood that fit properly without the gaps and most importantly these wooden elements were at proper lengths. The length of the diagonal element was probably the most difficult to achieve, but it was crucial to place the diagonal element properly on the horizontal HSS in right place and also place it on base plate in such a way that it will be relatively easy to weld.

Cutting diagonal elements based on wooden templates and welding them in place

The wooden templates have saved the day. This was the best decision we have made in this project. Based of each wooden template, we have hand cut its copy from the HSS using a plasma cutter. Placing and then welding up the steel diagonals was relatively an easy task since they have fitted perfectly. The biggest gap was about 1/8 in one element and another element came out 1/4″ short. At the end I highly recommend using templates for similar tasks

The top view of the timber wood retaining wall on a slope in forest  environment, London, Ontario, 2022
The top view of the timber wood retaining wall on a slope in forest environment, London, Ontario, 2022