Investigation is the first of the four fundamental activities included in integral sewer management (chapter 1). To a reasonable extent, it is to cover all performance aspects of the drain and sewer system in order to create the basis for the next step (the evaluation of the capacity of the drain and sewer system). The obtained results serve to show compliance to due diligence, and also as the basis for the determination of all activities to be carried …

Apart from damage that has an impact on the structural condition of the system, the age and position of the existing infrastructure, the geotechnical data of the bedding zone and the surrounding subsoil, as well as the potential of damage that could put existing buildings and other supply and drainage facilities at risk should also be included in the considerations for all structural investigations [ [EN752:2008]].

The structural investigations can …

External inspection comprises all measures that are carried out either from the ground surface or specifically prepared explorations. They serve to identify the bedding conditions of the existing sewer or structure, i.e., especially bedding defects and cavities in the pipe run. These have an influence on the reliability, capacity and durability of the soil/pipe system. In many cases, they account for damage of the sewer and also surface settlement …

For a first estimation of the feasibility and to determine a succeeding direct inspection program, the above-ground walkover inspection of the pipe run inclusive of a visual inspection of the street- or ground surface of the respective section of sewer in the catchment area is obligatory.

In the process, possible effects of damage in sewer systems or drain systems (e.g. in the area of the manholes, inspection chambers, catch basins and street surface) …

With regard to structural engineering, geotechnical investigations are understood to include all analyses required from the fields of (engineering) geology, hydrogeology, geophysics, soil mechanics, rock mechanics, environmental engineering and chemistry to describe and assess both soil and rock. The analyses involve bench tests as well as field tests [ [DIN4020:2010]].

In the case at hand, it is the target of a geotechnical exploration, which is …

As a result of the walk-over inspection ( (Walk-over inspection of the pipe run in-situ)) or internal inspection ( (Visual inspection from inside - Qualitative condition acquisition)), a direct external inspection of the embedment and/or sewers and structures might become necessary. In the process, either subsoil explorations are carried out or the respective sewer sections or structures are laid open in order to inspect their outer walls and embedment …

Direct explorations are natural or artificial explorations that provide for an inspection of the soil or rock and its sampling.

The direct exploration methods allow for the determination of layers borders, types of soil and rock and rock- or soil-mechanical parameters. Samples can be taken to be classified later on in terms of their appearance and to be analysed from a geological point of view.

EN ISO 22475-1 [ [DINENISO22475-1:2007]] sets “the technical …

Indirect explorations are explorations that allow for conclusions about the subsoil by a given correlation between physical indicators and soil- or rock-mechanical parameters.

Indirect explorations include:

• Sounding (dynamic probing and pressure probing)
• Geophysical methods of measurement ( (Geophysical subsoil exploration))

The results of measurement gained from this exploration method cannot be attributed directly to the subsoil parameters, but …

For reasons of economic efficiency, the composition and the characteristics of the subsoil and the groundwater conditions can only be tested at a number of selected locations, particularly in the case of linear structures (such as supply and drainage pipes).

The scope of an engineering geological analysis must always be in reasonable proportion to the measure that is to be implemented. As an example, the geotechnical inspections can be omitted in …

During damage assessment, but also in the decision for a suitable rehabilitation method, sound knowledge of the bedding conditions of the existing sewer is very important, because, in many cases, these conditions represent the causes of damage. Large-scale insights on the condition and load bearing capacity of the bedding and information on local inhomogeneities (such as bedding defects, cavities, concrete casings) can be gained by means of geophysical …

Seismic technology is by far the most important and prevailing method of exploratory geophysics used to explore deposits such as oil, gas and coal). From an (environmental) engineering point of view, it also provides essential structural information.

The seismic methods make use of elastic wave and wave field transmission in the subsurface to gain direct insights into its complex structure.

The underground has an impact on the propagation of seismic (…

Magnetism

(Image: Physical measurement principle of magnetism [Lenz97])

At ground surface level, the topmost layers of the underground have a strong impact on the Earth’s magnetic field. In applied geophysics, not the layers themselves are considered, but rather the structures contained in them, such as iron substances, bunkers, tanks, beams, pipelines, scrap, containers and reinforced concrete foundations. Often, these iron substances are not the …

Gelo-electrics

(Image: Carrying out a geo-electrical measurement [FI-DMT98])

Geo-electrics are used to locate objects and structures that have a different electrical resistance than their environment. A distinction can be made between galvanic and capacitive geo-electrics. In the first case, the electrodes and measuring probes are put into the ground in the form of metal stakes and thus, galvanically coupled. In the case of the capacitive coupled geo-…

Selection and evaluation of geophysical methods

The above-mentioned geophysical methods allow for a non-destructive detection and assessment of the invisible areas outside the sewer wall and below the road surface in the in situ subsoil and the backfill of the line trench.

The advantage of geophysical methods of measurement is the access to a useable statement involving relatively low expenses, the possibility to interpret single point information …

The standard method in a planned inspection in the context of self-monitoring and operational inspections of a drain and sewer system is the visual inspection from inside for a qualitative acquisition of the structural condition ([ [EN13508-2:2011]]) as well as the operational condition.

The systems that are applied for the inspections have to be adequate to entirely and explicitly capture all visible damages and conditions in drains and sewers, manholes, …

Man-accessible drains and sewers can be visually inspected by accessing them on foot or with sewer TV equipment.

This method of inspection requires specific preparatory measures and the work has to be done under consideration of occupational health and safety standards (chapter 8 - in progress).

A direct inspection by walking through the drain and sewer system on foot is recommended to be carried out in nominal sizes not smaller than DN 1,200. Amongst …

Generally, the indirect visual inspection is carried out in non-accessible drains and sewers with clear heights between 100 mm and 1,200 mm. Given special limiting conditions, smaller or larger cross sections can also be inspected using this method.

The indirect visual inspection is done using:

• Sewer mirroring
• Sewer TV inspection

Sewer mirroring

The oldest and simplest way to gain insight on the interior condition of straight-alignment, non-accessible …

Inspection systems based on video camera technology are characterised by an individual control of image recording and a simultaneous description of the actual condition. For that reason, they are also called inspection systems with direct image control and –evaluation. There exist different camera types with analogue and/or digital signal output. They are distinguished into axial view cameras and pan and tilt cameras.

Axial view cameras have only …

In recent years, inspection systems entered the market which, in contrast to the analogue video camera technology used in the conventional sewer TV inspection, are based on digital photo technology with a pre-set control of the image recording and a subsequent description of condition [ [Stein05]] [ [Hunger2002]].

This method uses high-definition fully spherically, hemispherically or cylindrically recording wide angle cameras with fisheye objective …

The hybrid camera technology combines the video camera technology and the digital photo technology in one system. An example for this functional principle can be found in the inspection system “RPP^®DuoVision Hybrid Camera” of the company RICO.

RPP^® DuoVision Hybrid Camera

The hybrid camera, also called “Tilt-Rotor-camera probe SR 100 Zoom/RPP” [ [FI-RICO]], is equipped with a pan and tilt mechanism and two camera modules that face each other and have …