Injection fixing of the less-like soil of Mongolia

02027


INTRODUCTION
Injection chemical fixation of soils is an artificial, purposeful transformation of the building properties of soils by treating them in their natural occurrence with various chemical and cement mortars with appropriate various additives [1;2;3].Injection fixing is used for soils with water permeability, including subsiding loess, loess-like sandy loam and loam [4;5;6].With injection fixing, the natural structures and composition of soils are not disturbed.As a result of silicification and cementation by injection, in almost all cases, the irreversibility and durability of the physical and mechanical properties acquired by soils are ensured [7;8;9].

METHODS AND MATERIALS
Laboratory and field studies to determine the parameters of deformation and strength of the fixed soil were carried out according to the standard methodology.In the test of injection fixation of subsiding soils, 20%, 30% and 40% solutions of liquid glass with a density of 1.19 g/cm3 were used, as well as a cement mortar prepared at a ratio of 1:20, 1:30 and 1:40 from Portland cement grade 450.The basic technological scheme of injection experiments is shown in Figure 1.

Laboratory tests.
Figure 1 shows the S=f(P) curve obtained by determining the settlement corresponding to a stepped load up to 1600 kPa using an odometer to determine the modulus of deformation of the fixed soil.The value of the K chem coefficient is determined by the ratio (1) depending on the type of mortar used, for example: according to the results of our tests, in the case of fixing with 40% liquid glass, K l.glass = 1.394, and when fixing 1:40 with cement mortar, K cem = 2.480.When substituting the deformation modulus coefficient into the formula, the formula for determining the deformation modulus of chemically fixed soil takes the form: When loading soil samples with a pressure of 12.5 ... 1600 kPa on an odometric device, the settlement is 1.3 mm in soil reinforced with a 40% liquid glass solution, and 1.18 mm in soil reinforced with a 1:40 cement solution.The test results show that the precipitation of reinforced soils by the chemical method is reduced by 1.5 ... 2.5 times, depending on .The results of testing the soil, reinforced with a solution of liquid glass, to determine the compressive strength =f(t) is shown in Figure 3. σ The results of soil tests, the curves of dependence of cement fixed with mortar on compression σ=f(t) are shown in Figure 4.As can be seen from the above parameters, after 28 days, the average compressive strength of soil reinforced with a 40% liquid glass solution is 39.0 kPa, and the average compressive strength of soil reinforced with a 1:40 cement solution is 137.0 kPa , which is 3.3 times higher than that of solution-strengthened liquid glass.The filtration capacity was determined on the KF-00 device, the values of the filtration coefficient are given in Table 2.The design parameters of the strength of the reinforced soil were determined using a dynamic protative automatic density meter, including the frontal resistance of the dynamic probe q s , the adhesion force c, the angle of internal friction φ, the density ρ, the humidity W and the degree of humidity S r , which are compared in the diagrams and presented in the figures 6...11.According to the results of a comparative analysis of the above X-ray images, it was found that the sandy loamy soil contains mainly quartz, albite, stilbite-Ca, kaolinite and anorthite, with albite making up 46-61% and quartz 31-48%, and the total amount is 92-96%.

The results of fixing the under-compacted soil of the backfill of the foundation and floor.
Production complex according to class II liability classification with modern automatic technological equipment and machines.4-5 years after commissioning, under-compacted soils for backfilling the equipment foundation with depths of 7.0; 4.0; 2.75 and 2.0 m, as well as bulk soils, led to the fact that the underground floors of the workshops sank by 30 ... 50 cm due to vibration from the operation of equipment and moisture.In connection with the possibility of further subsidence of the soil, we developed a design solution for cementing backfill soils.To fulfill the requirements for backfilling and soil dumping, it is necessary to have a deformation modulus E ≥ 10.0 MPa. and the results are shown in Table 3.

CONCLUSIONS
The sediment of the soil fixed with a solution of liquid glass, corresponding to a pressure of 100 kPa, is 1.76 times less, the sediment of the soil fixed with a solution of cement is 2.0 times less.The sediment of the soil fixed with a solution of liquid glass, corresponding to a pressure of 500 kPa, is 2.15 times less, the sediment of the soil fixed with a solution of cement is 2.45 times less.The sediment, corresponding to a pressure of 1600 kPa, in soil fixed with a solution of liquid glass is 2.5 times lower, and fixed with a cement solution, 2.75 times lower.As a result of fixing with silicate and cement mortar, the filtration capacity of the soil decreases by 17...28%, and it can be seen that the injected solutions filled the pores between the solid particles of the loess-like soil.
According to the results of the repair work on grouting the backfill of the foundations of buildings and equipment, the value of the porosity coefficient decreased by 15%, and the deformation modulus increased by 3.34 times, demonstrating the high efficiency of the grouting method.
Based on the results of experimental and theoretical studies, an effective method for fixing subsiding soil, taking into account the regional characteristics of Mongolia, is cementation using a cement slurry prepared with a composition of 1:40 and grade 450.

Fig. 2 .
Fig.2.Dependence curves S=f(P) of soil fixed by chemical methodsThe results determined by the average modulus of deformation of the reinforced soil by the chemical method are shown in Table1.

Fig. 3 .
Fig. 3. Dependence curves of compressive strength on the number of days of exposure of samples σ=f(t) of soil fixed with liquid glass

Fig. 4 .
Fig. 4. Dependence curves of compressive strength on the number of days of exposure of soil samples σ=f(t) fixed with cement mortar Soil typeFiltration coefficient, m/day Soil with a natural structure 0,60 Soil fixed with liquid glass 0,43 Soil fixed with cement mortar 1:40 0,32Field natural tests.The design scheme of the test and the location of sampling points for determining the mechanical parameters of the reinforced soil are shown in Figure5.

Fig. 5 .
Fig. 5. Calculation scheme and points for the selection of reinforced soils

Fig. 12 .
Fig. 12. Dependence curve S=f(P) according to the results of tests of fixed subsidence soilThe analysis of the S=f(P) dependence graph, carried out on the basis of the results of odometric tests of unreinforced and chemically reinforced sandy loamy soil, revealed the following dependencies: In the compression test of reinforced soil with a solution of liquid glass, the values of settlement corresponding to a pressure of 50 kPa were determined by 1.8 times, and the magnitude of the settlement corresponding to the same pressure of the settlement of the soil, reinforced with a solution of cement, is 2.1 times less.Deformation modulus of fixed soil.After 28 days for the reinforced soil in the field, digging with measurements at a depth of 1.25 m, with a diameter of 0.95 m, and at a depth of 1.75 m with a diameter of 1.20 m, enlarged soil monoliths were obtained with a length (height ) 1.1-1.2m (Figure13).

Fig. 13 . 7 E3S
Fig. 13.Photo of measuring the geometric dimensions of the fortified subsidence soil.When comparing the results of field and laboratory tests and analytical calculations, it was found that the average modulus of deformation of soil reinforced with a solution of liquid glass

Fig. 14 .
Fig. 14.The result of X-ray dipractographic tests of natural soil

Fig. 17 .Table 3 .
Fig.17.Photo of the process of carrying out work on cementing the soil backfilling the foundation of an industrial buildingTable 3. Comparison of backfill soil performance before and after grouting № Indicators Indicators of soil before grouting

.
Deformation modulus for calculating enlarged and loose subsidence soils

Table 2 .
Comparison of average values of filtration coefficients of fixed soils