Okay, let's break down the considerations for installing your PVC duct bank transitions to RGS elbows and conduits rising through a new slab on grade.

Why Sleeves Might Be Considered


Differential Movement/Settlement

The primary reason for using sleeves is to allow for differential movement between the conduits and the slab. Here's why this is important:

Soil Settlement

Even with well-compacted soil, some settling is inevitable. If the conduits are rigidly embedded in the concrete, the settling can put stress on the conduits, the RGS elbows, and the gear. This stress can lead to cracking, deformation, or even failure of the conduits or connections. A sleeve allows the conduit to move slightly independently of the slab.

Thermal Expansion/Contraction

PVC and RGS (steel) have different coefficients of thermal expansion. Temperature changes will cause them to expand and contract at different rates. If rigidly embedded in the concrete, this can cause stress and potential damage over time.

Vibration

Vibration from heavy equipment or other sources can be transmitted through the ground. Sleeves help to isolate the conduits from this vibration.2.

Future Modification/Replacement



Easier Replacement

If a conduit needs to be replaced in the future (damage, new technology, etc.), it's significantly easier to pull the old conduit out and install a new one through the sleeve than it is to break up concrete.

Future Expansion

Sleeves provide a degree of future flexibility. While you might not be planning it now, having the sleeves in place could make future conduit additions or re-routing easier.3.

Concrete Protection



Protect the PVC

The sleeve provides a physical barrier between the rough, abrasive concrete and the relatively softer PVC. This can help prevent damage to the PVC conduit during the pour.

Prevent Concrete from Entering the Conduit

Sleeves ensure the opening is kept clear.

Why You Might Not Need Sleeves (and Considerations)


Small Conduit Size and Minimal Movement

For very small conduits (perhaps 1" or less), and if the slab is lightly loaded and the potential for settlement is minimal, the need for sleeves may be less critical. However, 4" is a substantial size.2.

Proper Backfill and Compaction

If the backfill around the conduits is extremely well-compacted, and the soil is stable, the risk of significant settlement is reduced. However, "extremely well-compacted" is difficult to guarantee, and even slight settlement can cause problems.3.

Flexible Couplings

Some engineers will allow direct embedment of conduits if flexible couplings are used near the slab penetration. This allows some movement and expansion without stressing the conduit.4.

Cost

Sleeves do add to the material and labor cost of the installation.

Installation Procedure Without Sleeves (If Permitted - NOT RECOMMENDED WITHOUT APPROVAL)

If you were to pour the slab directly around the RGS elbows and conduits, here's how it would generally be done (again, proceed with caution and only with approval):1. Proper Support

Securely support the elbows and conduits before the pour to ensure they remain perfectly vertical and in the correct location. Use bracing and supports that will not move during the pour.2.

Accurate Placement

Precisely position the elbows and conduits at the correct height relative to the finished floor.3.

Thorough Concrete Consolidation

Vibrate the concrete thoroughly around the conduits to eliminate air pockets and ensure a good bond.4.

Surface Finishing

Carefully finish the concrete around the conduits to create a smooth, level surface.5.

Protection During Curing

Protect the exposed RGS elbows and conduit threads during the concrete curing process.6.

Bonding

Bond the RGS conduit as required by code

Recommended Practice: Use Sleeves

In your situation (4" PVC to RGS elbows), I strongly recommend using sleeves. The benefits of mitigating differential movement and allowing for future modifications outweigh the additional cost in most cases. It's the more professional and robust approach.

Here's how I'd approach it


Sleeve Material

Use a suitable material for the sleeves. PVC pipe, steel pipe, or even cardboard forming tubes designed for concrete work can be used. Choose a size that provides adequate clearance around the 4" conduit (e.g., 6" or 8" sleeve).2.

Sleeve Length

The sleeve should extend a few inches below the bottom of the slab to allow for backfilling and soil movement, and a few inches above the finished floor.3.

Secure the Sleeves

Securely anchor the sleeves in place before the pour. Use stakes, bracing, or formwork to prevent them from shifting or floating during the concrete pour.4.

Fill the Annular Space (Considerations)

After the concrete has cured and the conduit is installed, the annular space (the space between the conduit and the sleeve) should be addressed.

Sealing

Many prefer to seal the top of the annular space with a flexible sealant to prevent water, dirt, and debris from entering. This sealant should be flexible enough to accommodate some movement.

Foam Backer Rod

Insert a foam backer rod into the annular space to control the depth of the sealant.

Important Considerations



Local Codes and Regulations

Always consult local building codes and regulations. They may have specific requirements regarding sleeves for conduit penetrations. Some jurisdictions require sleeves.

Engineering Specifications

If the project has an engineer, follow their specifications. They may have specific requirements based on the soil conditions, building load, and other factors.

Electrical Inspector

Discuss your plans with the electrical inspector before starting the work. They can provide valuable guidance and ensure that the installation meets their requirements.

RGS to PVC Transitions

Use listed and approved fittings for transitioning from RGS to PVC. These fittings are designed to provide a secure and watertight connection.

In summary, while it might* be possible to pour the slab directly around the conduits, the risk of problems in the future is significantly higher. Using sleeves is the best practice for ensuring a reliable and long-lasting installation. Always prioritize safety and compliance with applicable codes and regulations. Flag for review