HYDROGRAPHIC SURVEY

HYDROGRAPHIC SURVEY

26/05/2021

Hydrogeological survey to clarify distribution laws, physical properties and chemical composition, dynamics and dynamics of groundwater.

Hydrogeological surveying is the collection of information necessary to enable the design of groundwater lowering systems. Well done planning and carrying out the field surveys, along with the methods used for drilling, exploration, inspection... The next step is to analyze the data collected during the process. field survey.

The successful design of such projects relies heavily on realistic estimates of the permeability coefficients of the various soil and rock layers present below the construction site. The permeability test methods, their scope of application, and their relative values ​​and limits are complex.

1. Purpose of hydrogeological survey

A particular problem for designers of groundwater-lowering projects in many cases surveys are primarily designed to provide information for the design of permanent structures. Information required for the design of temporary structures (including lowering of the groundwater table) is often overlooked. This problem can arise when the survey protocol makers do not have the appropriate expertise or experience. In addition, the Investor's lack of information may lead to them not being informed of the need to lower groundwater for the project; therefore, they will not plan to collect relevant hydrological information.

2. Hydrogeological survey plan

All field investigations should be planned and designed so that they provide necessary information to designers and construction managers. There is no such thing as "standard" because standard geological conditions are absent, where two adjacent geological points can be completely different.

When planning a hydrogeological survey, we need to answer the following questions:

  • What do we know about the survey area?
  • What do we know about the survey area?
  • What do we need to know?

3. Hydrogeological survey steps

  • Collect relevant documents
  • Preliminary survey of the site
  • Perform experiments
  • Report

4. Geological parameter determination

Any survey should determine the nature, depth, extent and orientation of the floor below the site. Together, these parameters describe the "surface", often based on the results of test pits, boreholes, geophysics, etc. Determination of soil composition is an essential part of model selection. groundwater calculations required to enable the design of a groundwater lowering system.

5. Determination of groundwater characteristics

Ground water level

The most visible and common form of groundwater monitoring is the images obtained in dug pits and boreholes. Unfortunately, there are two important limitations to the accuracy of the figures obtained in this way:

  1. The water level may not be correct due to rain or water being added to the excavated hole, or the borehole wall is blocked to prevent normal water infiltration.
  2. In soils with poor permeability, it takes a long time for the water level to flow into the borehole to equalize with the actual conditions.

Monitoring groundwater level changes over time

Sampling and testing the chemical composition of water

6. Determination of permeability

Permeability (also known as conductivity) is an essential parameter determined for the design of groundwater lowering systems. There are many methods of determining permeability, some of which have been in use since the nineteenth century. Existing methods can be classified into four main categories:

1. Laboratory test (including particle size analysis and permeability test)

2. On-site experiments (small scale) (including drilling holes, piezometer and special experiments such as pouring water, scooping water...)

3. Large-scale on-site testing (including pumping and groundwater control tests)

4. Other methods (including geophysics, visual assessment, and inversion from numerical models)

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