Subgrade Strengthening Research Articles

Structural forming of soil composites using as a pavement subgrade strengthening

The article substantiates the possibility of obtaining composite materials with improved functional properties to strengthen the subgrade, containing technogenic soil stabilized by an additive based on a gelling polymer. The introduction of technogenic soils into composites will not only reduce the consumption of expensive materials, but also solve a complex of acute environmental problems. Composite materials can be used in the construction of structural layers of road pavements, foundations of buildings and structures, sites for various purposes, for the prevention and elimination of defects in the foundations of engineering structures during their construction, reconstruction and repair, including in permafrost areas. Stabilized technogenic soils are more durable, frost-resistant and waterproof, which makes them applicable for creating impervious curtains in hydraulic structures and sealing storage facilities for hazardous substances. The cryogenic effect on a composite material allows one to vary its properties within a wide range and modify its macroporous structure. Studying the process of structure formation of the resulting organic-inorganic materials, consisting of macromolecules of high-molecular substances and inorganic inclusions that have undergone cryogenic treatment, will make it possible to specifically regulate their performance characteristics. The best values of strength characteristics were obtained for samples with a stabilizing additive concentration of 100 g/l. The resulting composite materials are hydrophobic, frost-resistant, characterized by a compressive strength of 2.3–6.5 MPa and a thermal conductivity of 0.19–0.20 W/(m·K). Data from differential scanning calorimetry and thermogravimetry and IR spectroscopy revealed that the binding of mineral particles by a stabilizing additive occurs due to the formation of organomineral complexes with the participation of clay minerals and the restructuring of hydration shells. SEM data indicate that crystallinity zones formed due to hydrogen bonds of hydroxyl groups of neighboring polymer chains can participate in the formation of the composite structure. An increase in the number of cryogenic treatment cycles promotes additional structuring and strengthening of the polymer phase due to the formation of additional nodes of the supramolecular network, ordering of crystallinity zones and the appearance of compacted areas in the structure. Computed X-ray tomography revealed an increase in the density of the composite upon drying, which helps to increase its strength characteristics. The structure of the sample is characterized by heterogeneity of the pore space, which is characterized by the presence of both fine-porous and large-porous regions, which determines its thermophysical properties.

РАСЧЕТНЫЙ АНАЛИЗ ПОВЕДЕНИЯ ПОДШПАЛЬНОГО ОСНОВАНИЯ ПРИ ЕГО СТАБИЛИЗАЦИИ ГЕОСИНТЕТИЧЕСКИМИ МАТЕРИАЛАМИ

Common feature of reconstruction and construction of new railways is in the need to have a high-quality track subgrade. Meanwhile, geosynthetic materials play an important role, for example, for improving bearing strength of the subgrade and for the increase of service life of track structure in whole. Hardness of the «subgrade - geogrid» composite system and the change of the stress-strain condition of unstabilized sleeper bearing in the comparison with the stabilized one are estimated with the use of the finite element modeling. According to results of culvert tests the paper presents comparison of plate settlement on the subgrade stabilized by the geogrid and unstabilized road-metal subgrade. Moreover, the authors assess the efficiency of subgrade strengthening by the geogrid with the use of numerical modeling.

A Critical Review of Subgrade Soil Reinforced with Geo-synthetics

Recently, the application of geosynthetics in the reinforcement of weak subgrade is expanded dramatically. However, selection of the geo-material that fits site conditions and soil type is crucial to achieving the success of the overall performance of such improvement. Also, the road life and cost construction are significant keys for evaluating this type of ground treatment. This paper presents an overview of the subgrade strengthening with geosynthetics to acquire a better understanding of the technique and to provide a clear guide for transportation and geotechnical engineers. The rutting failure along with its main causes are highlighted briefly. The types of geosynthetics, their applications and functions are also listed. Besides, the effect of soil type and properties on the efficiency of geofabrics-subgrade reinforcement are presented. Moreover, the effectiveness of geosynthetics on the road’s life and construction costs are discussed. Findings of the reviewed studies referred to the contributions of the technique in strengthening the soft subgrade, extending the service road life, reducing the construction cost and reducing the associated rutting deformation. Most studies presented in this paper have proven the efficiency of utilizing geosynthetics in the pavements to minimize the vertical stress in the subgrade under the wheel path. However, the influence was related to the geo-material type and site-specific conditions.

Application Research of New Cementitious Composite Materials in Saline Soil Subgrade Aseismic Strengthening

Saline soil affected by earthquakes and groundwater can lead to subgrade subsidence and collapse in highway construction. Consequently, considering the potential activity of the waste slag and magnesia, new cementitious composite materials used in solid saline soil were developed in our study. The unconfined compressive strengths of the saline soil solidified by the new cementitious composite materials with a combination of magnesium oxide, calcium oxide, gypsum, and mineral powder and cement were investigated, and the optimum dosage proportion of the new cementitious composite material for solidifying saline soil was determined; then the SEM, EDS, and XRD of the saline soil solidified by the new cementitious composite materials and cement were analysed. The research result showed that the saline soil solidified by our newly developed cementitious composite material showed compact internal structure and uniformly distributed soil particles; moreover, the new cementitious composite material exhibited a favourable solidifying effect on harmful ions in saline soil, and the Cl− trapping capacity of the new cementitious composite materials was stronger than that of cement. Finally, our developed cementitious composite material was applied to saline soil subgrade strengthening, and the displacement, acceleration, excess pore water pressure, and damage degree of the subgrade strengthening by our newly developed cementitious composite materials decreased remarkably; therefore, our newly developed cementitious composite material can improve the seismic behaviour of the saline soil subgrade and show potential future engineering application value.

Effect of Freezing‐Thawing Cycle on the Mechanical Properties and Micromechanism of Red Mud‐Calcium‐Based Composite Cemented Soil

The environmental issues caused by solid waste have become increasingly serious. Adding additive is considered as an effective measure to improve the performance of the cemented soil. Therefore, the feasibility study of solid waste such as red mud and desulfurization gypsum used in composite cemented soil is in urgent demand. In this study, the mechanical properties and durability to freezing‐thawing cycle of red mud‐calcium‐based composite cemented soil (RMCC) were analyzed through compressive strength test, resistivity test, and freezing‐thawing cycle test. The action mechanism of RMCC was revealed through a series of X‐ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) test. The results show that the optimal red mud content in RMCC is 12%. As the freezing‐thawing cycle progresses, the difference in resistivity and pressure sensitivity of RMCC gradually weakens. When the freezing‐thawing cycle reaches 7, the pressure sensitivity characteristic of RMCC is lost. The change in resistivity and pressure sensitivity can be used to characterize the damage caused by the freezing‐thawing cycle. Combined with XRD and SEM analysis, the presence of minerals such as K2Ca5(SO4)6·H2O and (Ca, Na)2(Si, Al)5O10·3H2O play a key role in fixation of alkali metal elements, and the coordination of CSH gel cementation effect and AFt filling effect has a significant impact on mechanical properties. The study provides an effective way to the utilization of red mud and desulfurization gypsum in subgrade strengthening.

Conceptual Review of Subgrade Strengthening for Low Bearing Capacity Soil and U-Shaped Subgrade Panel

Conceptual Review of Subgrade Strengthening for Low Bearing Capacity Soil and U-Shaped Subgrade Panel

Renewable Energy By-products (REB) Adaptation Successes in Environmental Geotechnics: A Review

The place occupied by Geotechnics and Geo-environmental Engineering in the 21st century renewable energy cycle has been reviewed and results have shown that for a complete, closed and perfect renewable energy process, the geotechnical engineering processes of soil stabilization, soil improvement and subgrade strengthening and the civil engineering procedures of concrete production should be credited and recognized. Biomass and the by-products of the renewable energy conversion process; fly ash, granulated slag, charcoal and ash have been in use in the stabilization operation without well positioned and full realization that these complete the cycle by kicking back the by-products which should have been disposed as solid waste thereby creating a loop, back into the renewable energy cycle. This is to justify that Geotechnical Engineering and its allied areas maintain a very important place in the renewable energy cycle by closing the loop that should been created should the by-products of renewable energy be disposed as solid waste.

Subgrade Strengthening on the Sections for Cars Interchanging with Axle Load of 25 T and More

The article deals with the problem of strengthening of the subgrade located on the sections that have the interchange of cars with the axle load of 25 tons and more.The issues of the subgrade behaviour were studied on the example of the Eastern test site with regard to geotechnical and permafrost conditions for the construction and maintenance of subgrade.The main directions to the subgrade strengthening are referred to the following:1)Strengthening of the top of subgrade;2)Providing the stability of the sloping parts of subgrade;3)Providing the carrying capacity of the weak, including thawing, roadbeds.

Subgrade strengthening of roads and railroads as planar geotextile reinforcement

The proper quality of construction of roads and railroads can be achieved by strengthening the of the foundation bed. Measurements and tests the number and order of the layers of geotextile layer of ground indicate the effectiveness of technical solutions involving the reinforcement laid horizontally. The offer technical use of the geotextile reinforcement in the ground layer substrates of roads indicates the possible effectiveness of the strengthening of the subsoil of roads and is also included in this article.

Effects of Freezing-Thawing Cycle of Compressibility of Cement Soil

Based on the safety and durability in the cement soil engineering about the pits anti-seepage, embankment impermeable walls and subgrade strengthening in the frozen regions and the retaining walls in foundation pits, the experiments on the compressibility about the cement soil under freezing-thawing cycle, infiltrated and other environmental-action conditions have been carried out and the influential laws of environmental actions on the compression parameter of cement soil have been obtained. The results show that the various environmental actions may have influences on compressibility of cement soil at different levels, and the environmental effects on the compressibility of cement soil in the engineering applications and designs, such as impermeable walls or in the frozen regions, should be taken into account, and the void ratio and the coefficient of compressibility will increase with the increase of freezing-thawing cycle times and infiltration time but the compression modulus will decrease with the increase of freezing-thawing cycle times and infiltration time so that the curve regression equation about the void ratio, the coefficient of compressibility and compression modulus varying with the freezing-thawing cycle times and the infiltration time has been established. The results are significant and valuable to the safety and the durability of cement soil engineering.

Infiltration Time Effects of Compressibility of Cement Soil

Based on the safety and durability in the cement soil engineering about the pits anti-seepage, embankment impermeable walls and subgrade strengthening in the frozen regions and the retaining walls in foundation pits, the experiments on the compressibility about the cement soil under freezing-thawing cycle, infiltrated and other environmental-action conditions have been carried out and the influential laws of environmental actions on the compression parameter of cement soil have been obtained. The results show that the various environmental actions may have influences on compressibility of cement soil at different levels, and the environmental effects on the compressibility of cement soil in the engineering applications and designs, such as impermeable walls or in the frozen regions, should be taken into account; and the void ratio and the compression parameter will increase with the increase of freezing-thawing cycle times and infiltration time but the compression modulus will decrease with the increase of freezing-thawing cycle times and infiltration time so that the curve regression equation about the void ratio, the compression parameter and compression modulus varying with the freezing-thawing cycle times and the infiltration time has been established. The results are significant and valuable to the safety and the durability of cement soil engineering.

Application of Dynamic Drainage Consolidation Method in Subgrade Strengthening

This paper introduces the application of dynamic drainage consolidation method in subgrade strengthening. Treatment result shows that the standard values of foundation bearing capacity are totally more than 120kPa，settlement of post –construction is less than 150 mm and differential settlement is less than 100mm，and the reinforced Depth of subgrade is about 9 m.

Comparative analysis of the experimantal research results of the subgrade strengthening by small-deformable layer

In the article the results of comparative analysis of variants of strengthening the ground bed by the smalldeformable layer are presented.

Investigations on soft clay subgrade strengthening using geocells

In the last two decades geotextiles are being increasingly used as tensioned/tensile members. When used for reinforcement functions, a geotextile has to yield high resistance at low strains, especially for structures where allowable rut depths are low and the life span of the structure is long. This necessitates the use of high modulus geotextiles with adequate roughness. The present study aims at investigating the efficacy of the geocell alternative and the effect of the cell geometry and relative density of the backfill. Experimental and finite element procedures have been adopted to study the above parameters. Soft saturated marine clay was used as subgrade while sand was used as backfill material. Monotonic loading was applied in plate load tests. The experimental results were simulated in a three-dimensional finite element ( fe) procedure using ANSYS, a general purpose package. Considerable improvement in the load and reduction of settlement was observed from the experimental results. The results of the fe analysis were used to study the improvement in stiffness and stress distribution.

Erratum for “Subgrade Strengthening of Existing Airfield Runways”

Erratum for “Subgrade Strengthening of Existing Airfield Runways”

Subgrade Strengthening of Existing Airfield Runways

A number of subsurface treatment techniques are found to have definite potential for strengthening existing airfield pavements. Basic requirements for subgrade treatment beneath existing airfield pavements are examined. Changes in pavement structural behavior caused by subgrade strengthening are theoretically analyzed. It is shown that subgrade strengthening beneficially affects airfield pavement structural response. Techniques for treatment of the subgrade beneath existing pavements are reviewed. These techniques are evaluated relative to their potential for subgrade strengthening below existing airfield pavements. It is concluded that: (1) drilled-hole and pressure injection lime; (2) mixed-in-place pile; and (3) post hole pile procedures have definite potential for strengthening subgrades beneath existing airfield pavement systems.