Precast Concrete Products

Introduction

The Vanstone Three Piece Manhole is a kit-form light duty precast concrete inspection / service chamber suitable for underground telecoms services.

The kit consists of a base or floor, a wall section and a lid section including a cast iron cover and frame. The walls are usually supplied with knock-out holes to the customers' requirement. Up to 22 of such holes of 110mm diameter have been supplied in the past.

Dimensions:

• Inside: 600 x 450 x 500mm deep
• External: 680 x 530 x 650mm height
• Wall thickness: 40mm
• Weight (total): 290kg

Service entry holes:

Any configuration. Rather specify more holes than less. Typical:

• Long sides: 7 x of 110mm diameter
• Short sides: 4 x of 110mm diameter
• Base: 1 x 40mm diameter drainage hole.

Click here for detail of holes

Installation

The total external height of the manhole is 650mm. It is often preferred that the rim of the manhole project above the ground or paving by at least 75mm. This determines the depth of excavation. Excavate for the manhole and over-excavate for the sides sufficiently to allow for compaction equipment. Where sufficient accuracy of excavation can be achieved, only slight over excavation is required, which may be backfilled with a cement stabilized gravel or mass concrete if preferred.

Backfilling should always be at least as strong and serve the same purpose as the surrounding soil. To aid the drainage of occasional rain water, a subsoil drain may be installed under the manhole. This can be in the form of a small sump under the centre hole that can hold extra water or a system that drains water away from the manhole. Simply over-excavate to the size required and fill with any constant size crushed stone.

In the bottom of the excavation, prepare a true and level 50mm thick bed of riversand, crusher sand, fine clean gravel (particle size < 6mm) or cement stabilized topping material. Place the manhole base or floor carefully on the bed ensuring proper and even seating. Place the wall section on the base, ensuring that it is the right way up when looking at the service holes. Use a thin layer of cement mortar between the walls and the base if seating is not snug. Place the lid section on top of the walls and make sure that the walls penetrate into the recess at the bottom of the lid and is not half-in, half-out. The manhole can now be used to install sleeves, cables and other services. Simply knock out the required holes with a hammer (no more than 4lbs). Full water tightness is not achievable.