(Image: Protective strip of at least 2 ft (60 cm) in width at the side of the trench)

The insertion method depends on the selected trench shoring system. Is is mandatory to follow the manufacturer‘s installation specifications in this respect.

It has to be ensured that the installation of the trench shoring proceeds in line with the excavation process, so that the trench walls never stand unsupported beyond the allowable angle.

For the safety of the …

(Image: Formation of a gap during the insertion: The lack of an uninterrupted force-locked connection during the installation process results in the risk of settlings of the lateral soil and damages to the completed surface)

To prevent debris from falling into the trench, the shoring has to be at least 2 in (0.05 m) higher than the ground level. For depths of more than 7 ft (2 m), the trench lining has to be at least 4 in (0.1 m) higher than the ground …

Headwalls of shored trenches, in firm cohesive types of soil, are allowed to be unsupported up to a depth of 6 ft (1.75 m) and a width of 4 ft (1.25 m).

When exceeding these values, trench headwalls are to be shored in the same way as side walls [DIN4124:2002].

(Image: Entry of soil caused by water due to a leaking headwall shoring) (Image: Securing the headwall of the shored trench by means of a steel plate (end plate)) (Image: Securing the headwall …

The minimum length of shoring is to be implemented particularly in short-term construction sites (i.e. sectional installation of pipe). In the case of sectional pipe installation, the length of a trench section to be secured with trench shoring system shall be such that the subsequent work can be carried out in the unsecured area at a depth of no more than 1.25 m (4.1 ft). In this case, the face of the trench shall be secured by shoring (e.g. by …

(Image: Example for non-compliance to the minimum required distance) (Image: Example for non-compliance to the minimum required distance)

It has to be ensured that road vehicles and, in particular, construction equipment, are kept at a sufficient distance from the trench in order to prevent overloading the trench shoring.

The following minimum distances are to be kept for horizontally and vertically lined trenches:

• Generally allowed road vehicles and …

(Table: Minimum required distances for vehicles and construction equipment in accordance with DIN 4124a)

The installation methods of trench lining elements are basically classified into the insertion method and the cut and lower method.

The insertion method involves first excavating the trench, and then inserting the shoring elements into the temporarily stable trench. Worker access to the trench is only permissible upon the successful installation of the shoring.

In the cut and lower method the soil is excavated in stages between the panels, which are alternatingly forced into the soil one side at a time.

In the cut and lower method the soil is excavated section-wise in-between the panels, while the lining elements are forced into the in situ soil simultaneously on both sides.

Insertion of linear shoring support elements with roller frame in practice: The uninterrupted force-locked connection between the trench shoring and the subsoil is guaranteed.

For the installation of pipelines and sewers in areas with groundwater, the trench has to be kept free of water. There are three water retention methods available for that purpose:

• Open dewatering

• Groundwater lowering using shallow tube wells (well-points)

• Groundwater cut-off (cement grouting, freezing process, chemical process, …)

Subsequently, the first two options will be considered in detail.

(Image: Groundwater lowering using wells – Detail: …

Open dewatering involves simultaneously collecting accruing groundwater water during the excavation process. This process is performed at about 20 in to 40 in (50 cm to 100 cm) ahead of the excavation, and requires stable types of soil (such as rock), coarse gravel or cohesive types of soil and generally low permeable soils to be effective. The groundwater can be directly pumped or allowed to seep to sumps at the boundaries of the trench, where it …

(Image: Groundwater lowering using wells)

In the groundwater lowering method, vertical wells as well as required piping and pumps are installed around the planned trench or construction pit (in the case of large construction pits also within the pit) prior to the excavation process.

Compared to the open water retention method, groundwater lowering by means of wells allows for significantly deeper lowerings. The design type and dimensioning of the well …

(Image: Installation of wellpoints for groundwater lowering using gravity drainage) (Image: Groundwater lowering using gravity drainage- mode of operation) (Image: Installation of wellpoints for groundwater lowering using gravity drainage)

Basically, we distinguish between gravity drainage and vacuum drainage systems.

In the case of gravity drainage, the lowest groundwater level can be found in the well pipe. Consequently, due to gravity, the water …

Instead of vertical wells, horizontally arranged filters or drainage pipes can also be installed next to the excavation (or even below larger excavations).

The so-called horizontal water collection significantly reduces the water quantity to be pumped. However, the additional costs for the installation of this system are only economical for long-term construction measures.

The construction of sewers is still often carried out in the form of open cut construction. Depending on the design, this results in different pipe-soil systems with different external loads on the sewer.

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

• rules and regulations;
• requirements for planning, tendering and construction of the pipeline zone, the shoring and the components and building materials;
• procedures for dewatering and
• process sequences of the open construction method.