Geophysical surveys in engineering surveys on the highway “Duplicate of the Dzhubga-Sochi Highway”

In December 2008, a team of specialists from Moscow State University Geophysics in the amount of two people and two specialists from Sochitranstonnonproekt TO-44 LLC carried out works under the agreement “Construction of the central highway of Sochi“ The backbone of Kurortny Avenue ”from km 172 of the federal highway M-27 Dzhubga-Sochi (r. Psakhe) before the start of the bypass of the city of Sochi PK0 (r. Agura) with the reconstruction of the road section from the street. Strawberry to Kurortny Avenue, Krasnodar Territory, (Phase II, Zemlyanichnaya Street to the River Sochi). ”

The main task of engineering and geophysical surveys was to study the geological structure of the upper part of the section along the axis of the designed structure (tunnel) to a depth of 10 to 60 meters, including:

• determining the depth and configuration of the bedrock boundary under the overlying sediments;
• study and assessment of the power and configuration of the zone of weathering eluvium);
• groundwater level determination (GWL);
• mapping of watering zones in the areas of distribution of water of a vein-fracture type with a forecast of likely areas of unloading to the level of the designed tunnel;
• mapping of the zones of spreading of weak and disturbed soils, corresponding to the zones of crushing and increased fracturing.

To solve the above problems, two methods were used: frequency sounding for detailing the upper part of the section to a depth of 0–30 meters and TSB (method of establishing a field in the near zone) for detailing the section to a depth of 10–80 meters.

Method of work

PR method

When performing works using the ChZ method, innovative equipment “HF-EM” was used (OOO MSU-Geofizika, Moscow). The equipment is intended for geophysical work using high-frequency electrical prospecting methods (shallow depth fault, DEMP). The equipment set consists of a portable high-frequency square-wave generator (up to 1 A) and a meter synchronized with it.

When using the equipment of frequency electromagnetic sounding, the field is excited and measured with the help of antennas (multi-turn frames) located horizontally or vertically up to 100 meters from each other at frequencies from 512 to 4 kHz. The maximum depth of research does not exceed the distance from the source to the receiver. The change in the electrical properties of rocks with depth can be traced by changing the frequency. Frequencies switch automatically, the registration time at each point is a few seconds. The received data is copied to the computer for interpretation.

On the Central profile, as well as on the transverse profiles, measurements were made of the vertical and radial field components using the ChZ method with a step of 10 meters and a spacing of 40 meters.

According to the results of soundings, 1D mathematical modeling was performed using the EM-1D program (Pushkarev P.Yu.).

ZSB method

For operation using the TSB method (probing the formation of the field), the serial equipment Cycle-7 was used. An equipment set consists of a generator of bipolar, rectangular current pulses (up to 20 A) and a meter synchronized with it, a notebook computer such as a notebook and a power supply battery.

The TSS technology also does not require galvanic contact of antennas with the surface. A generator antenna (square from 25x25m wire) and receiving antenna (square from 20x20m wire) were deployed at the sensing point.

Using the PROBA-WIN software, the curves obtained during measurements were reviewed and edited to further process and interpret the data.

According to the results of soundings, mathematical modeling was performed using the EM-1D program (Pushkarev P.Yu.).

Results of work

According to the results of the work, 7 geoelectrical sections were built, the first - the central one - passing over the designed tunnels and 6 into the cross of the lying profiles

The results show that rock resistances vary in the range: from 1–2 Ohm • m to 200 Ohm • m.

In general, a three-layer structure is characteristic of all cuts. The first layer has a resistance of 120-125 Ohm • m and a power from 0 to 7 meters, which is characterized by low-resistance anomalies with a capacity of up to 2 meters. In the second layer, with a resistance of 12-14 Ohm • m, with a capacity of from 0 to 25 meters, local anomalies of relatively high resistance (30 and 20 Ohm • m, respectively at pickets 29 and 43) and low-resistance (3 Ohm • m at pickets with 16th to 21st) facilities. The third layer with a resistance of 6–9 Ohm • m appears under the southern portal and in the central part of the profile. The resistance of 200 Ohm • m is characteristic for the northern part of the portal, and also in the southern part of the portal from the picket from the 12th to the 22nd.

On the background of a three-layer geoelectric section, several local anomalies can be identified. The first anomaly is from the 10th to the 14th picket, the second from the 46th to the 49th picket of the central profile and the third on the transverse profile 3 - within the 7th picket.

According to the results of the office processing of field data, the depth of geophysical surveys was approximately 30–40 m according to the CZ method, and 75–80 meters according to the CPS method. three anomalous zones not characteristic of this type of section were also identified.

The lack of geological data makes it difficult to interpret the results of mathematical modeling, perhaps local and vertical electrical conductivity anomalies are associated with tectonic disturbances and landslide processes. During construction, these places should be given special attention, since they represent a danger to further exploitation and need more detailed study.

Conclusion

1. As a result of the field work carried out by the ChZ, KSB method and mathematical modeling, geoelectrical sections were made along the Central and Section Profiles 1 - 6.
2. The work area is characterized by the presence of three geoelectric layers, on the one hand, and vertical conductive zones, on the other hand.
3. The nature of the vertical conductive zones is possibly related to the zones of tectonic disturbances and, as a result, their watering.
4. For geological interpretation of the anomalies obtained, it is necessary to attract the results of drilling.

The authors of the report express their deep gratitude to the team of Sochitranstonstonelproject TO-44 LLC for assistance in carrying out the field work and discussion in preparing the report, which, undoubtedly, only improved the present work.

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