what kind of conduit for underground electric?

There are several types of conduit that can be used for underground electric installations, including:

PVC Conduit: This is a common type of conduit used for residential and commercial electrical installations. It is affordable, lightweight, and easy to install. PVC conduit is available in a range of sizes and can be used for both direct burial and concrete-encased installations.
HDPE Conduit: High-density polyethylene (HDPE) conduit is a flexible, durable, and long-lasting option for underground electrical installations. It is resistant to corrosion, abrasion, and impact damage, making it ideal for harsh environments.
Rigid Metal Conduit: Rigid metal conduit (RMC) is a heavy-duty conduit made of galvanized steel or aluminum. It is strong and durable, making it ideal for industrial applications where high levels of protection are required.
Intermediate Metal Conduit: Intermediate metal conduit (IMC) is a lighter-weight version of RMC. It is also made of galvanized steel or aluminum and provides a higher level of protection than PVC conduit.
Electrical Metallic Tubing: Electrical metallic tubing (EMT) is a thin-walled conduit made of steel. It is lightweight, easy to install, and offers a high level of protection against physical damage.

The choice of conduit will depend on the specific requirements of the installation, such as the environment, the amount of protection needed, and the type of cables being used.