Depending on the local code requirements and (or) clients' preferences, we install two types of manhole vault structures: block vault or precast vault.
The block vault is a solid, heavy-duty structure that measures 5 feet in external diameter and 4 feet in internal diameter. The upper portion tapers in as it reaches the top, so it can accommodate a suitably sized cover. It is constructed with tongue-and-groove cement blocks which interlock for strength and stability. These blocks are installed in mortared layers, and the individual blocks are also mortared. The entire structure is then brushed with concrete slurry to enhance both appearance and structural strength. In all of our years of service, we have never had to replace any of our block vaults for any reason.
The precast vault is normally installed only in villages where regulations require it. It has the same four foot internal diameter as a block vault, but the external walls are somewhat thinner than block vault. The precast vault consists of large, heavy cylindrical and conical cement layers, and its final overall appearance is similar to that of the block vault. Because these layers are very heavy they have to be lowered down into the excavation by means of a special truck (The Parks' Crane Truck) adapted for that purpose. These layers are similarly sealed with mortar.
For stability, both vaults have to be set on the original, undisturbed soil. This soil surface under the vault structure is leveled and smoothed with sand before the vault structure is installed. To facilitate access to the valves and the pump, cast iron steps are installed inside the block vault. The precast vault requires special plastic steps for the same purpose.
The cavity between the side of the vault and the original, undisturbed soil is also filled with sand to avoid having the ground sink around the vault. It costs Parks' Plumbing more to haul away dirt and bring in sand or gravel back-fill but the final product of a smooth lawn is well worth the extra time and money put into the job. Parks' is always concerned about the final product and we are always looking for ways to improve our systems.