Engineering and geological surveys for construction

Recommendation points

• Who conducts engineering and geological research
• What are the objectives of the survey
• The order of work
• Receiving special data
• Applying report results

When developing building land, the study of hydrogeological conditions is one of the first stages. Who is doing this research, what should be included in the report, and where will the data be used? We tried to shed light on common questions about studying the structure of the soil under the future house..

Who conducts engineering and geological research

An organization providing expert assessment of geological conditions must meet two requirements. The first is the admission of SROs in engineering surveys for conducting this kind of research, the second is the corresponding technical and intellectual base. And if everything is relatively clear with the licensing of activities, then the contractor’s possession of special equipment, equipment and personnel of special qualifications is difficult to establish “by eye” before the contract is concluded. Mandatory required:

1. Means of mechanization for well drilling and sampling.
2. Equipment for transportation and storage of samples.
3. Research laboratory with certified equipment and accredited personnel.

Omitting one of these points can greatly distort the results of the examination or make them completely irrelevant. The surest way to identify a truly bona fide geotechnical survey contractor is to rely on the experience of previous developers who have made favorable technical decisions based on available geomorphology reports..

In the matter of choosing a contractor, it is very important that the latter conduct an open and transparent activity, and each stage of interaction with the customer takes place on the basis of a clear technical task and is stipulated in the contractual documentation.

What are the objectives of the survey

The main task of geotechnical research is to collect data on the composition and structure of the soil at the construction site, as well as on the basic principles of the interaction of this soil with engineering and construction structures..

Construction geology includes three components: the study of soil on the ground, geodynamics in interaction with engineering objects and regional statistics. The latter helps to get a comprehensive idea of ​​the geological phenomena in the selected area, predicting the development of the situation and the influence on it of the processes occurring in adjacent territories.

In purely practical terms, geological exploration is needed for three main reasons. The most common is the need to calculate the structure and type of foundation for further drawing up a construction project. Basically, it all comes down to determining the suitability of a building site, calculating the supporting capacity of the soil and the characteristics of its behavior in different weather periods.

The second goal of the survey is to determine the possibility of high-quality planning and terracing of areas with complex relief. Moreover, the report contains the results of not only geomorphological studies, but also geodetic ones. Finally, the third and most trivial goal is to discover already existing engineering communications and structures, to find a way to build without critical impact on them, including in the future for the next decades..

The order of work

The contractor’s actions are easy to control. Since the study of soil samples takes most of the time, wells are drilled first on the site. Depending on the number of storeys and the mass of the building, the depth of the fence can be from 5 to 15 meters. Previously, the contractor must obtain an opinion on the composition of sedimentary rocks in the study area and make a decision: at what depth does the direct impact from engineering structures cease to determine the thickness of the studied section.

At a minimum, four wells are drilled at the extreme points of the site with a step-by-step control of the outgoing core and taking samples at set depths. Almost immediately, a picture of the geomorphology of the site opens: at what depth are layers of different types, what is their slope, thickness, are there water-bearing horizons in the cut, what is their thickness and water behavior.

In addition, wells can be drilled on the red lines of the future building. The properties of the obtained samples clearly indicate the bearing capacity of the soil, its plasticity and saturation with water. Thus, data on general geomorphology helps to organize site planning and drainage of the area adjacent to the building, and local samples help to accurately calculate the type, configuration and structural strength of the foundation. This helps to avoid wasting material in excess of the necessary measure and ultimately lightens the construction budget..

In parallel with taking soil samples, another group of specialists collects and summarizes archived data on studies already carried out in neighboring or close territories. The information obtained is analyzed until the completion of the collection and study of samples in the laboratory (7-10 days), then the project manager prepares (5-7 working days) an expert report with a forecast of the development of the geological situation for the life of the building. The received data is transmitted to the person or organization that draws up the construction project.

Receiving special data

For complex construction projects, especially if they are located within urban areas, a number of additional surveys may be required. The most common jobs include the marking of underground utility lines, the location of municipal engineering systems and, sometimes, hydrogeological exploration to find a suitable water source..

Survey methods remain the same: taking soil samples and working with the city’s architectural department to obtain information about the location of objects hidden under the ground. If it is necessary to assess what the mutual influence of the new structure with neighboring structures may be, it is possible to build a computer model. Data analysis usually includes a forecast for the next 50 or 70 years, which requires meticulous calculations and outstanding professionalism. In such cases, it is recommended that you personally communicate with the person in charge of the project..

Sometimes a radical change in weather conditions during the year requires field work in several stages, in some cases with the drilling of new wells. The change of groundwater level, the movement of layers is studied, the dynamics of frost heaving is visually estimated and the actual depth of freezing is established. The chemical composition of soil and water samples determines the potential degree of corrosive effects on building structures..

Applying report results

The finished report on engineering and geological surveys includes several sections. The first is the terms of reference and input data – information obtained from geological maps, reports on surveys in neighboring territories, data on the density of development and the proximity of special objects (overpasses, high-rise buildings, underground tanks and others like them).

The second and third sections describe the geological and hydrogeological conditions of the object, respectively. Data for them is provided by keeping a log of the withdrawal of samples during drilling of wells, the number and placement of which in the report must be indicated. In fact, these two sections are nothing more than basic data on the geomorphological section. It is the basis for foundation design, site soil planning and slope leveling..

The fourth section contains the physical properties of soils: density, porosity, moisture saturation, plasticity, composition – only about two dozen indicators, including the results of frost tests. These data are used as secondary when choosing waterproofing and thermal protection of foundations, choosing a protective layer of concrete and its grade for water permeability..

The final part of the report contains explanatory and recommendatory notes, as well as all the necessary illustrations: diagrams of changes in soil parameters in the annual cycle, plans, section drawings. So that the report data can be accepted by a third-party organization for the development of a construction project, copies of the SRO certification and the contractor’s contacts are attached to the survey results for further interaction with him without the participation of the customer.