TECHNOLOGIES FOR INCREASING SUBGRADE STABILITY OF LOW-HEAD HYDRAULIC STRUCTURES

УДК 626/627:624.138

Abstract

This article examines the critical issues of soil stabilization and various technological methods utilized to improve soil mechanical characteristics in the subgrades of low-head hydraulic structures. Due to the intensifying climate change impacts and escalating water scarcity across the Central Asian region, the sustainable management and safety of existing water infrastructure have become matters of paramount socio-economic importance. This study specifically focuses on the complex engineering and geological conditions prevalent in the Amudarya river delta, which is characterized by highly deformable, water-saturated, and compressible soil layers. Underestimating these geotechnical properties often leads to a significant loss of structural strength and stability, triggering catastrophic failures. The paper evaluates the efficiency, advantages, and limitations of modern stabilization techniques, including deep pile foundations, sheet piling, and chemical grouting methods. While classical approaches ensure structural reliability, their high implementation costs restrict widespread application. The findings emphasize that incorporating local construction materials into these engineering workflows presents a viable, cost-effective pathway to drastically reduce project budgets without compromising structural integrity. Continuous regional research and historical precedent analysis are proposed as vital tools for optimizing future hydraulic designs.

Аннотация

В данной статье рассматриваются актуальные вопросы стабилизации грунтов и различные технологические методы, применяемые для улучшения механических характеристик грунтов в основаниях низконапорных гидротехнических сооружений. В связи с усилением последствий изменения климата и растущим дефицитом водных ресурсов в Центральноазиатском регионе, обеспечение безопасности и устойчивого управления существующей водной инфраструктурой приобрело первостепенное социально-экономическое значение. Особое внимание в исследовании уделено сложным инженерно-геологическим условиям дельты реки Амударьи, для которой характерны сильнодеформируемые, водонасыщенные и высокосжимаемые слои грунта. Недооценка этих геотехнических свойств часто приводит к существенной потере прочности и устойчивости оснований, вызывая катастрофические разрушения сооружений. В работе оцениваются эффективность, преимущества и ограничения современных методов стабилизации, включая устройство глубоких свайных фундаментов, шпунтовых ограждений и методы химической инъекции (цементации). Хотя классические конструктивные подходы обеспечивают высокую структурную надежность, их значительная стоимость ограничивает повсеместное применение. Результаты исследования подчеркивают, что использование местных строительных материалов в этих инженерных процессах представляет собой экономически эффективный способ радикального снижения бюджета проектов без ущерба для надежности конструкций. В качестве важнейших инструментов для оптимизации будущих гидротехнических проектов предлагается проведение непрерывных региональных исследований и анализ исторического опыта.

Keywords: low-head hydraulic structures, measure, technology, subgrade, stabilization, soil improvement, safety.

Ключевые слова: низконапорные гидротехнические сооружения, мероприятие, технология, основание, укрепление, улучшение свойств, безопасность.

Introduction

Water resources are continuously depleting in the Central Asian nations, progressively exacerbating the region's economic challenges. Climate change is giving rise to anomalous weather patterns, and these complexities are highly likely to persist in the future. Over the next decade, climate change coupled with increasing water consumption in neighboring countries is projected to reduce Uzbekistan's water intake from the Amudarya and Syrdarya rivers. Consequently, the processes of drought and desertification could intensify further, posing a severe threat to the population's standard of living. As this declining trend in water resources persists, the widespread implementation of water-, energy-, and resource-saving technologies has become a matter of paramount importance to offset water losses and mitigate shortages.

In recent years, due to water scarcity, significant attention has been directed toward the design, construction, and sustainable operation of low-head hydraulic structures. In Uzbekistan, low-head hydraulic structures vastly outnumber large-scale ones. Considerable research and practical development have been carried out by leading scientists and specialists in the field of designing and constructing these low-head hydraulic structures.

Research Objectives

The primary objective of this study is to analyze and evaluate efficient, cost-effective technological methods for improving subgrade stability under the challenging engineering-geological conditions of the Amudarya delta. To achieve this, the study targets the characterization of regional deformable soils, assessment of modern structural reinforcement techniques, and exploration of pathways to minimize construction costs using local materials.

Materials and Methods

The Law "On the Safety of Hydraulic Structures," enacted in its new edition in 2023, was developed with the aim of maintaining the country's existing water management facilities in a technically sound condition, ensuring their safety, and achieving reliable operation. A significant portion of these water management facilities has been in operation for more than 40 years. This necessitates timely repair, rehabilitation, and reconstruction, alongside equipping them with modern apparatus and instrumentation to ensure their safe and dependable functioning [1-3].

In the Amudarya delta, deformable soils—which are highly susceptible to deformation and rapidly lose their structural properties under the influence of external factors—are widespread. In modern technical literature, the concept of "deformable soils" refers to soils characterized by full water saturation, excessively high moisture content, high porosity, and extreme compressibility, which are sensitive to dynamic loads. Geotechnical field investigations in the delta region indicate that these weak soil layers are predominantly characterized by an unstable void ratio (e = 0.85 - 1.05), a critically low modulus of deformation (E = 5 - 8 MPa), and a high coefficient of permeability (k = 1 - 3 m/day) within the seepage zones.

The depth of these complex soil layers varies from a few centimeters to tens of meters or even more. In such contexts, underestimating these structural mechanics and characteristics leads to an immediate loss of strength and stability in the subgrades of low-head hydraulic structures, potentially triggering catastrophic failures in the future. Such occurrences have frequently been recorded in the practice of hydraulic engineering, causing substantial socio-economic damage [4,5].

The reliability of subgrades for low-head hydraulic structures and the cost reduction of their construction works largely depend on the accurate assessment of soil properties in the foundation, the efficiency of the selected technological methods and dimensions, and the quality of execution of these works [6,7].

Taking into account the geological complexity of the construction site, when deformable soils are present in the foundations, the core requirements of regulatory documents mandate special measures. These include the excavation and removal or replacement of deformable soils, their compaction or stabilization, and the utilization of sheet piles or pile foundations (Figure 1).

Figure 1. Technology for subgrade stabilization using various types of piles

Note on Figure 1: Figure 1 presents a generalized technological sequence for pile deployment, serving as a structural baseline for comparing classical deep foundation workflows with alternative chemical soil-modification interventions.

Results and Discussion

At present, despite being complex and expensive, these methods of subgrade stabilization are recognized in construction practice as the most safe, reliable, and effective. Due to the high cost of the aforementioned technological methods, alternative special measures have been proposed by means of improving the properties of the foundation soils [8].

For concrete low-head hydraulic structures built on complex, multi-layered, deformable subgrades, it is critical to ensure their stability and mitigate seepage and deformation risks [9]. Technical literature and research reports highlight effective and cost-efficient technologies that can be successfully applied under such conditions:

Structure siting – this involves selecting a potential construction site with a homogeneous and incompressible subgrade for the design and construction of the structure;

Extending the seepage path;

Maintaining a low ratio of height to dam length;

Installation of vertical and horizontal drainage systems;

Grouting for subgrade stabilization (cementation, bituminization);

Application of geotextiles (geogrids for uniform load distribution, reinforcement, and stabilization of weak soils);

Utilization of anti-seepage devices;

Utilization of pile foundations and sheet piles;

Utilization of local construction materials [10].

To specify the composition of local construction materials proposed for geotechnical workflows in the Amudarya delta, research shows that utilizing local fine dune (barkhan) sands, high-plasticity local clays, and industrial by-products such as fly ash and slag from regional thermal power plants can act as highly effective mineral additives or soil replacement components. When mixed correctly, these local materials form a stable matrix that significantly improves soil density.

Currently, the subgrade grouting method is widely utilized in hydraulic engineering practices across our republic. Its primary advantage lies in its low labor intensity. Reinforcing the foundations of structures undergoing emergency repairs or reconstruction using any method other than grouting requires executing large volumes of manual earthwork and concrete work under highly constrained and cramped conditions. Grouting methods successfully eliminate these complications.

However, the main drawback of this method is the difficulty in ensuring the homogeneity of the stabilized mass and monitoring the quality of reinforcement. The stabilization process is invariably non-uniform: strength varies across different zones, and certain minor sections may remain untreated. Since the volume of stabilized zones is typically measured in tens or hundreds of cubic meters, monitoring every single cubic meter (and especially every cubic decimeter) through drilling or sounding is exceptionally difficult. For these reasons, soil chemical stabilization remains relatively less common.

Based on the options outlined above, it can be concluded that the technologies applied to reinforce subgrades and ensure the stability of hydraulic structures are both complex and expensive. However, utilizing local construction materials provides a viable pathway to reduce these costs. Therefore, studying historical precedents and conducting specialized scientific research remain critical instruments for development.

Conclusion

The worsening water scarcity and changing climate dynamics in Central Asia underscore the critical need for the safe, reliable, and sustainable operation of water management infrastructure. In Uzbekistan, where low-head hydraulic structures comprise a substantial portion of the water distribution system, addressing subgrade stability under complex engineering and geological conditions—particularly within the deformable and moisture-saturated soils of the Amudarya delta—is paramount to preventing catastrophic structural failures and minimizing socio-economic losses.

This study analyzed various engineering interventions aimed at reinforcing foundations and mitigating risks associated with seepage and soil deformation. While classical structural methods, such as sheet piling and deep pile foundations, offer maximum reliability, their financial and technical demands often limit broad implementation. Similarly, chemical grouting techniques, despite minimizing intensive labor in cramped operational zones, present significant quality-control and homogeneity challenges across large subgrade masses.

To reconcile the trade-off between technical reliability and economic constraints, the integration of water-, energy-, and resource-saving technologies combined with the utilization of local construction materials emerges as a highly viable alternative to substantially reduce overall project costs. Consequently, continuous assessment of soil mechanics, thorough evaluation of historical engineering precedents, and focused scientific research remain crucial tools for developing optimized, cost-efficient, and structurally sound stabilization technologies tailored to the region's specific geological challenges.

References:

1. Law of the Republic of Uzbekistan "On the Safety of Hydraulic Structures," No. LRU-865, August 20, 2023. Tashkent, 2023 (In Uzbek).
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