The present invention relates to construction, particularly, to geotechnical and soil investigations, and can be used for field tests by statically loading soils using in situ piles, which are, for instance, load-bearing structural elements of retaining walls, excavation support, embankment support and others, which carry mainly horizontal and moment loads.

In this industry, the standard and most commonly used test method is testing soils by static horizontal loading using a pile [1], where the load is applied to the pile head by using standard hydraulic equipment. While testing soils using a pile, the stress-strain state of the pile - soil base system is being investigated using both conventional deflectometers and state-of-the-art transducers and equipment, whereby the load-bearing capacity of a pile for horizontal loading [2] and/or the factor of proportionality (stiffness factor) of the soil base [3] are determined according to various methods.

Field methods of testing soils using piles for moment loading are totally missing from the regulatory documents. However, there are reliable theoretical methods in regulatory and reference sources [3-7], which were proposed and tested in the Soviet Union and continue to be improved today by modern scientists [8-11], by means of which the stress-strain state of the pile - soil base system is determined when the pile is also subjected to moment loading.

As of today, regulatory documents of various countries and Ukraine [6] allow using numerous methods of calculation for structures and facilities in their interaction with the soil base using powerful design software packages. However, the regulations show that to determine their stress-strain state it is required to use adequate models of the soil base, the parameters of which are still to be identified on the basis of laboratory or field test methods to ensure the reliability of calculations [12].

The method that is closest to the proposed method by indirect characteristics is the method of static load testing of piles in subsidence soils [13], which involves the absence of contact (interaction) between the upper part of the piles and the soil base.

The task at hand is to determine the stress-strain state of the pile - soil base system below the bottom elevation of the excavation pit when the pile carry the horizontal load Ho and the moment load Mo at the bottom elevation of the excavation pit. The task at hand is solved by first excavating the soil around the pile from the surface elevation to the bottom elevation of the excavation pit, and the soil is tested using the pile from the surface elevation by applying to the pile head the horizontal load H in the direction of the load Ho and the moment load M in the opposite direction of the load Mo, which are equal to

H =H ₀ -

M -M ₀ -H ₀ ·/ø , where Ho is the design horizontal load on the pile at the bottom elevation of the excavation pit, kN;

Mo is the design moment load on the pile at the bottom elevation of the excavation pit, kN-m; lo is the upper part of the total length / of the pile from the surface elevation to the bottom elevation of the excavation pit, along which there is no contact with the soil base, m.

Fig. 1 shows a schematic diagram of the method of testing soils from the surface elevation 1 by the experimental horizontal load H and moment load M, using the pile 2, around which before testing the soil 3 was excavated from the surface elevation 1 to the bottom elevation of the excavation pit 4 to determine the stress-strain state of the pile - soil base system below the bottom of the excavation pit under the action on the pile 2 of the design horizontal load H and moment load Mo acting in the directions 5 and 6 respectively at the bottom elevation of the excavation pit 4.

The essence of the test method is that by testing soils using a pile from the surface elevation by the experimental horizontal load H and moment load M the real interaction (test) is simulated of the pile-soil base system below the bottom of the excavation under the action on the pile of the design horizontal load Ho and the design moment load Mo acting at the bottom elevation of the excavation pit.

The use of the method of testing soils from the surface elevation using a pile which transmits to the soil base the design horizontal and moment loads at the bottom elevation of the excavation pit, allows evaluating the stress-strain state of the pile-soil base system to justify and adjust the design of retaining walls before arranging an excavation pit. REFERENCES

1. DSTU B V.2.1-1-95. Soils. Field Test Methods by Piles. Kyiv: Ukrarkhbudinform, 1997, 58 p. (in Ukrainian).

2. DSTU B V.2.1-27:2010. Piles. Determination of bearing capacity on the results of field tests. Kyiv: Ministry for Regional Development and Construction of Ukraine, 2011, 11 p. (in Ukrainian).

3. Guidelines for the design of retaining structures from bored piles. Kyiv: NIISK, 1985, 36 p. (in Russian). . Guidelines for the design of pile foundations. NIIOSP named after N. M. Gersevanov, Gosstroy of the USSR. Moscow: Stroyizdat, 1980, 151 p. (in Russian).

5. Bases, foundations and underground structures: Reference book of the designer. Gorbunov-Posadov M.I., Ilyichev VA, Krutov V.I. [et al.]; under the general editorship of Sorochan E.A. and Trofimenkov Y.G. Moscow: Stroyizdat, 1985, 480 p. (in Russian). . DBN V.2.1-10-2009 Revision 1. Bases and foundations of buildings. Main design provisions. Kyiv: Ministry of Regional Development and Construction of Ukraine, 2011, 55 p. (in Ukrainian). . DSTU-N B V.2.1-31 :2014 Guidelines for the design of retaining walls. Kyiv: Ministry of Regional Development of Ukraine, 2015, 86 p. (in Ukrainian). . Luchkovsky I.Ya. On the bearing capacity of flexible retaining walls. I.Ya. Luchko vsky, A.V. Samorodov, S.V. Yesakova. Komunalne hospodarstvo mist. Kharkiv: O.M. Beketov National University of Urban Economy, 2012. Issue 105, pp. 62-68 (in Russian) . Luchkovsky I.Ya., Yesakova S.V. The deformation method of designing foundations. Kharkiv: Kollegium, 2016. 196 p. (in Russian)

10. Polyankin A.G. Research into the behavior of piles for horizontal and moment loads and improvement of the methods for designing the bases of pile foundations: Abstract of dissertation for the degree of Cand. of Tech. Sciences. A.G. Polyankin, Tyumen, 2014, 20 p. (in Russian) 1. Gotman A.L. Research into the behavior of large-scale bored piles for the horizontal load and their design. A.L. Gotman, A.Z. Gaysin. Bulletin of Perm National Research Polytechnic University. Construction and Architecture. Perm: Perm National Research Polytechnic University. Issue 9, No. 3, 2018, pp.14-27 (in Russian) Skochko L.O. Interaction between the multilevel retaining structures and the soil mass: Abstract of dissertation for the degree of Cand. of Tech. Sciences. L.O. Skochko. Kyiv, 2018, 24 p. (in Ukrainian) Inventor's certificate SU 401409730, E 02 D 33/00. Method of static tests of piles in subsidence soils. Design Bureau for reinforced concrete named after A. A. Yakushev and the State Institute of Urban Design (I.G. Ladyzhensky, V.S. Saburov). Publ. July 15, 988, Bull. No.26.