Joint Method For Concrete Substructures

Peter Rusche

SUMMARY:

The chosen design project was the creation of a new joint method for connecting various underground pipes to concrete substructures (or catchbasins). The current method used by contractors is a mortar mix. A mortar mix (concrete) is used to fill all the gaps between the pipe and the substructure hole. However, this method yields some restrictions. The main problem with this method is the time and labor it requires for completion. Secondly, since a concrete joint is formed, post-installation flexibility is minimal. Since mortar mix has a settling time, the joint is not fully complete until the mortar has cured (dried); this takes around a day's time. Once the mortar has cured, the joint allows for zero flexibility or movement of the pipe/joint. If the pipe or substructure was to settle over time, there would be no room for the pipe to move in any direction. Needless to say, once the concrete has cured, the pipe is irremovable.

 

Besides a mortar joint, there is also a rubber joint which can be cast inside the concrete catchbasin (during its production). However, this joint method is extremely expensive.

 

Ideally, a new design can possess the same positive attributes of a mortar joint, yet make improvements on the shortcomings of this method. The goal is to create a water/soil resistant method for joining/connecting various piping to concrete substructures without extensive time and labor, yet allowing for post-installation flexibility

 

This new method must create a water/soil resistant seal (or joint) between the pipe and the catchbasin. Installation of the joint method should be easy and simple. The design must allow for various entry angles (of the pipe), and axial pipe movement. The joint method should have a small completion time, allowing for immediate backfill to be placed upon the pipe. Due to the joint's underground application, it must be durable to surrounding conditions. Since there are a large range of pipe diameters, it is important that the design can be easily produced in various size increments. Since the design is striving to avoid the need of extensive time and labor, it is important that the cost saved by this is not offset by a large sales price (of the joint). Thus, it is important that the joint is relatively inexpensive.

 

With information gathered on what is already available, the generation of conceptual designs can now begin. One concept considered a joint that utilized an air tube. This air tube would create a seal between the substructure and the pipe. Another concept was a joint comprised of a gasket that would screw into the side of the catchbasin. Also considered was a joint created by an expanding foam material similar to that used for insulation. One concept featured a flexible rubber cushion used to create a seal. This would be the main element behind the final design chosen for the project.

 

This final design chosen utilizes a rubber loop, shaped like the letter ‘D'. Due to its shape, the cushion provides constant pressure against the pipe. This constant pressure creates and retains a water/soil proof seal. The joint uses a rubber collar, which fits flush against the outside of the catchbasin, to create a seal between the joint and the concrete substructure. Metal hose clamps will fasten the rubber cushion and collar to the joint. Since the joint will be inserted from outside of the catchbasin, the rubber collar will prevent the joint from being inserted too far into the hole. To keep the joint from sliding out of catchbasin, corner iron is installed on the joint (from inside the catchbasin).

 

After creating a prototype of this design, it is apparent that the D-shaped cushion works well. It allows for axial pipe movement, while retaining constant pressure on the pipe. The constant pressure ensures the constant seal of the joint. The joint also allows for complete removal of the pipe at any time, and thus, axial pipe movement. The outer rubber collar fits nicely against the outside of the catchbasin, and appears to make a great seal against the substructure. The corner irons do a great job at keeping the joint in place, and are easily installed.

 

Problems with the prototype occurred with the approximation of the D-shaped cushion. The cushion (in the prototype) was created using several strips of rubber raped around the joint. However, the design calls for a solid piece of rubber (this would have been impossible to create with the tools available to us). Thus, a completely waterproof seal is not possible in the prototype.