The essential differences of the optimised installation method in comparison to the traditional way of sewer installation by use of the open trench are:

• The use of special optimised concrete pipes

• No necessary working space at the sides of the pipe

• The use of a special linear type of lining

• The installation and connection of the pipes by means of a special installation system

• The backfilling of the embedment areas between the pipe and the in …

Criteria to be taken into account with regard to pipe design:

• Prevention of installation-related damages

• Simplified requirements for the installation of piping

• Suitability for automated installation

• Optimisation of the structural characteristics

• Beneficial interrelation between pipe weight and load bearing capacity

The result of the research and development efforts is the optimised pipe cross section for the nominal size range DN 20 in (500 mm) to DN 48 in (1200 mm), with a special reverse sealing collar.

(Table: Structural optimisation – Comparison to the integrated base pipe)

Reduction of the excavated quantity of soil

As the working space is no longer required, the trench width can be significantly reduced.

Compared to the “traditional” open cut method of construction, a considerably smaller quantity of soil has to be excavated (for DN 28 in (700 mm) about 25%), …

The following table shows that the cost for the pipe is only a small portion of the total cost of the open trench method. Therefore, it is recommended to evaluate the amount of savings due to reduced excavation in comparison to a higher pipe cost.

(Table: Relative construction costs for the conventional installation method)

(Image: Construction site equipment in case of the “optimised method of installation”)

The equipment required at the construction site is not entirely different compared to that of a "traditional" open cut method of construction.

Special characteristics are the modified linear shoring, the special installation system and the technology used for both the production of the flowable fill and (where required) treatment of the excavated soil.

The protection of the utility trench is done by means of linear shoring, which is specially designed to match the method of installation.

(Image: Initial excavation for the optimised method of installation) (Image: Insertion of the outer panels for the optimised method of installation) (Image: Insertion of the panel soldiers and outer panels for the optimised method of installation) (Image: Re-positioning of the panel soldiers (U-boogie car) for the …

Provided that the excavated soil is not suitable for a direct reuse, it is treated by means of the Kronenberger^® method:

The required mixed binder is evenly spread onto the soil mass to be treated (“covering” by means of a BigBag) and roughly mixed with the help of an excavator mounted mixing unit and/or …

Firstly, the granular pipe cover is placed onto the encased pipe and compacted.

Afterwards, the treated soil is placed into the trench in compacted layers. In the continuous removal process of the shoring elements it has to be ensured that the backfilled soil is always compacted against the native soil.

The top layer is then placed in accordance to the individual requirements based on the end use of the surface.

• Avoidance of the typical installation errors through the optimisation of the pipe shape, as well as the implementation of a partly automated installation method.

• Lower quantity of excavated soil as a result of a smaller trench width

• Lower volume of waste material to be dumped on landfill sites as the excavated material is reused

Conclusion: The optimised method of installation represents a more efficient, more environmentally sound, and less damage-…

Furthermore, …

This ensures that subsequent settlings or subsidence can be minimised or even prevented.

In order to prevent gross defects or deficiencies in the construction work and contractual debates on the evaluation of results obtained by means of different test methods and testing devices, it should be proceeded as follows (provided that nothing else is specified in the contract):

• Prior to the start of the compaction works, it should be stipulated that the same testing device is to be used for self-monitoring- and check tests.

• Provided that …

• If an agreement on the check test results cannot be achieved, direct test methods should be used for the compaction test.

• If, due to the characteristics of the different types of soil, the test methodology of direct methods is either too difficult or too time-consuming, or if direct test methods cannot be carried to the required extent due to the progress of the construction work, indirect test methods based on either verifiable rules of thumb …

The photos below summarise the currently available compaction test methods. In the following, their fields of application will be illustrated.

(Image: Core Cutter Method) (Image: Replacement Test) (Image: Dynamic Plate Load Test) (Image: Dynamic Probing)