(Image: Effects of uneven longitudinal load distribution)

What kind of impact have highly compacted bedding areas?

Highly compacted areas within the bedding layer lead to the formation of point loads (shown dotted thickly here) resulting in the cracking of the pipe.

The embedment consists of bedding, side filling and initial and main cover. The quality of the embedment is significantly influenced by the installation conditions of the pipes. Other topics of this module include flowable fill for trench backfill, optimized installation methods and compaction tests.

After completing this module, you will have a sound knowledge of:

• rules and regulations;
• requirements for the embedment zone and compaction of the trench backfill;
• process sequences of the open cut method;
• influencing factors to ensure high execution quality on the construction site;
• recognizing and assessing errors in construction.

(Table: Concrete Pipe Installation Considerations)

(Table: HDPE Pipe Installation)

(Table: PVC Pipe Installation Considerations)

A correct and proper installation will add to the useful life of ductile iron pipe. The [[DIPRA Installation Guide]] provides information about installation procedures, maintenance, and reccomended safety precautions. However, appropriate standards and specifications must be used according to project requirements.

The following table present major installation considerations of ductile iron pipe.

(Table: Ductile Iron Pipe Installation Considerations)

[[DIPRA Installation Guide]] specifies that "the trench laying condition with respect to the trench bottom is usually specified by the engineer or utility". There are five standard laying conditions described in [[ANSI/AWWA C150/A21.50]].

(Table: Standard laying conditions for Ductile Iron Pipe)

Below is a step-by-step overview of ductile iron pipe installation by the modified method A, as per [[ANSI/AWWA C150/A21.50]], according to [[DIPRA Installation Guide]].

(Table: Vitrified Clay Pipe Installation Considerations)

Connection of the individual pipe segments must be performed according to the manufacturer's specifications. In addition:

• When joining the pipes, suitable devices are to be used.

• The pipe section being installed is to be suspended freely during the joint connection, pushing or sliding the pipe on the prepared bedding is to be especially avoided with heavy pipes.

• If the pipes are not connected manually, only devices which allow for a controlled …

The connections of pipes to manholes and structures must be articulated. A concrete seat may also be installed under the connection to provide added support. The same applies if settlement is expected.

In addition, when connecting lateral sewer pipes to manholes, flexible watertight connectors should be used, unless otherwise specified in the owner's specifications.

After establishing the pipe connections, the bedding around the joint area must be carefully compacted. General recommendations and restrictions are given in table 2 in [[ASTM D2321–05]] for the foundation, bedding, initial backfill, embedment and final backfill.

(Table: General recommendations for installation and use of soils and aggregates as per [ASTM D 2321-05])

Which requirements of statics must be strictly observed?

The decisive factors are:

• Soil type

• Degree of compaction

• "Interface" for shoring (embedding condition B1-B4 as per [ATVA127])

• Layered placement and compaction (both sides evenly)

• Compaction of the side fill does not replace the haunch compaction.

• If necessary, ensure that the filtering capability towards the bedding layer beneath is always sufficiently stable.

The following table presents recommendations for installation and use of soils and aggregates for bedding and haunching in accordance with [[ASTM D2321–05]].

(Table: Recommendations for installation and use of soils and aggregates for haunching [ASTM D 2321-05])

(Image: Hand tamper)

What is meant by initial backfill?

Initial backfill (or cover fill) describes the area immediately above the pipe.

The thickness of the initial backfill in the compacted state is usually 12-in (30 cm). [[ASTM D2321–05]] recommends that the minimum initial backfill above the pipe crown should be 6-in (15 cm). The minimum initial backfill above the pipe connection should be at least 4-in (10 cm).

Only hand tools should be used in the …

The following table presents the use of soil and aggregates for the initial backfill, as well as embedment compaction recommendations, as per [[ASTM D2321–05]].

(Table: Recommendations for installation and use of soils and aggregates for initial backfill [ASTM D 2321-05])

What are decisive factors, which need to be considered during installation of the final (or main) backfill?

The requirements of statics must be strictly observed. The decisive factors are:

• Soil type (not to be "better" than in situ soil)

• Degree of compaction

• "Interface" for shoring

• Layered placement and compaction

• No use of heavy compaction equipment up to 3 ft (1 m compacted thickness) above the pipe crown

• Vibration energy of the compaction …

The following table presents the use of soil and aggregates for the final backfill as per [[ASTM D2321–05]].

(Table: Recommendations for installation and use of soils and aggregates for final backfill [ASTM D 2321-05])

The backfill of the embedment differs between four conditions [ATVA127]:

(Table: Cover Filling Conditions A1-A4 as per ATV-DVWK-A 127)