Backfill Layer Research Articles

CBR Mapping Prediction from 2D Resistivity Imaging Using Regression Following Archie’s Formula

Indirect geophysical methods are increasingly associated with direct underground methods in investigating the subsurface to address environmental and geotechnical problems and reduce the cost of underground studies. These methods make it possible to explore large areas with acceptable precision, time, and cost. The present study combines the electrical resistivity method with the California Bearing Ratio for exploring an area located west of the Nouakchott port in Mauritania. The study aims firstly to verify that the thickness of the backfill layer must be less than 2 m throughout the entire study area and secondly to map areas with low California Bearing Ratio values (<80%) indicating substandard backfill compaction using 2D Electrical Resistivity Tomography imaging survey and regression. The measured Electrical Resistivity values exhibit a good nonlinear regression with California Bearing Ratio, following Archie's equation. A map of California Bearing Ratio variation was derived from the Electrical Resistivity values, indicating the distribution and variation of soil strength in the study area. The results revealed that the backfill layer did not meet the standards, with approximately 35% of the total area having a California Bearing Ratio value below 80%. The areas with poor compaction requiring treatment were primarily located in the southern sector, followed by the middle and eastern sectors.

An experimental and numerical study of the strength development of layered cemented tailings backfill

The behaviour of a stratified backfilled stope in terms of strength development and stress distribution has not been well established in the field of rock engineering. Yet, the mining industries with massive ore bodies are looking into high production with a high standard of safety which is mainly governed by large excavation with backfill as a support system. It is difficult to fill these large excavations at one time. Therefore, a subsequent backfilling of the stope layer by layering is adopted, which results in a layered backfill structure. The purpose of this study was to explore the strength development, stress distribution and deformation across the stope supported by both layered and non-layered backfill. It has been observed that the backfill support system gain its strength with time, however, the layered backfill support system loses its strength when more layers are introduced, this is due to the shearing effect around the interfaces of the backfill layers. The impact of layering was validated by 3D numerical simulation. It is therefore concluded that non layered backfill support system are more suitable for stoping mining methods rather than layered support system.

Impacts of Tidal Oscillations on Coastal Groundwater System in Reclaimed Land

The impact of tidal oscillations on groundwater in coastal reclamation land demonstrates the complex hydrodynamic interaction between seawater and coastal hydrological aquifer systems. The tidal action not only affects the temporal variability of groundwater levels but also exerts a significant influence on the groundwater gradients of salinity within the subsurface aquifers. This study takes the Songmu Area as an example to investigate this ocean–groundwater interaction. Songmu Area is located on a peninsula with coastal land reclamation in Dalian, China. Field campaigns were conducted in this area to measure the tidal action and groundwater parameters in a coastal reclaimed area at artificial backfill layers with pressure and salinity sensors, where the tidal signal can influence groundwater levels and salinity up to a one-kilometer range of inland. Tidal changes in the surface of the sea can be broken down into a number of simple, regular harmonic vibrations, each of which is called a tidal split. The tide and groundwater data were extracted using an enhanced harmonic analysis method. The fluctuations of groundwater levels and salinity were decomposed in response to the periodic tidal oscillation. Various constituents of tide attenuation in the coastal groundwater system were investigated. Our research shows that there is an exponential reduction in the fluctuating amplitude of groundwater levels and the groundwater salinity as distance further inland from the coast. The constituents of tide M2 (the period is 12.42 h of semi-diurnal tides, S2 (the period is 12.00 h of semi-diurnal tides), K1 (the period is 23.93 h of full-diurnal tides), and O1 (the period is 25.82 h of full-diurnal tides) behave differently for the tidal wave propagation and salinity variability in the coastal aquifer of reclaimed land. Among those constituents, M2 and S2 exhibit a higher degree of attenuation compared with K1 and O1. Understanding the relationship between groundwater levels and tidal fluctuations in coastal backfill areas is crucial for effective groundwater management strategies and mitigating the adverse impacts of seawater intrusion. This study can serve as a good understanding for assessing the impacts of various mitigation strategies.

Finite element analysis of compaction load to investigate the stress-deformation behavior of soil geosynthetic composite mass: A case study

When building Soil Geosynthetic Composite (SGC) walls, fill compaction is normally carried out by operating a compactor in a general direction parallel to the wall face. In other words, a moving point or area load is often used to apply a compaction load on a newly installed soil lift. Pham (2009) and Wu and Pham (2010) demonstrated that the compaction-induced stress (CIS) caused by multiple passes of a compactor moving toward or away from a section can be calculated by taking into account the compaction load applied directly above the section under consideration using a simplified stress path proposed by Duncan and Seed (1986). Additionally, by simulating the compaction, the CIS due to fill compaction may be correctly assessed. The CIS resulting from fill compaction can also be accurately assessed by simulating the compaction load, such as by applying a distribution load on top of each backfill layer or a distribution load at the top and bottom of each soil layer, or by applying various widths of strip load to the top of each backfill layer. The objective of this study was to validate the numerical simulation of the compaction load to stress deformation behavior of SGC mass under operating stress conditions. In order to conduct the numerical analysis, data from both a full-scale instrumented SGC mass based on large-scale soil geosynthetic composite (SGC) experiments and a 6 m-high SGC (Pham, 2009) were employed. This study will examine a few SGC behavior parameters, including reinforcement strains, lateral displacements, and reinforcement strains. The objective of the FE modeling is to demonstrate the effect, emphasize the significance of the compaction conditions to the stress-deformation behavior of SGC mass, and validate the findings from the field-scale experiments and proposed model by Pham (2009) and Wu and Pham (2010).

Investigation on the Stress and Deformation Evolution Laws of Shield Tunnelling through a Mining Tunnel Structure

In the construction of a shield crossing an existing mined tunnel without load, it is imperative to develop corresponding design standards that reflect actual engineering force characteristics to ensure the successful completion of the tunnel construction. This study uses the MIDAS-GTS NX 2022 finite element software to facilitate the creation of a numerical model of a shield structure for an air-push-over mine tunnel project in Changsha, China while investigating the stress field’s evolution during shield construction and calculating the maximum positive and negative bending moments and maximum axial forces for different structures and other force states under various construction conditions. This study’s findings informed the design and construction optimisation of a shield tunnelling empty-push method. The outcomes of this numerical simulation led to several key findings: (1) The soil density exerted a significantly greater impact on the internal forces of the initial support structure than both the tunnel depth and soil Poisson’s ratio. Additionally, a sudden shift in internal forces occurred within the 300–350 mm range when the lining thickness was altered. (2) Factors such as the tunnel depth, soil density, soil Poisson’s ratio μ, and lining thickness similarly influenced the internal forces of the segment and the initial support. Notably, the backfill layer thickness significantly affected the segment’s maximum axial force, causing an abrupt change of approximately 300 mm. (3) It is essential to control the guide rail’s thickness under the shield machine equipment’s weight constraint to prevent it from becoming overly large.

Experimental Research on Diseases of Emulsified Asphalt Mortar Board for Ballastless Tracks

The dynamic performance of high-speed railway systems’ stability, comfort, and safety is an essential topic worldwide. The multiorder elastic modes of components are the key factors. It is the core technology to ensure the quality of the backfill layer of flexible cement-emulsified asphalt mortar (CA mortar) in reducing the elastic vibration structure of the car body. This research results from the manufacturability verification of the Beijing–Shanghai high-speed railway. Four theoretical model methods are used in the research: experimental observation data analysis, simplified orthogonal test, phase contrast and computational analysis, and grey relational analysis to improve the performance indicators of CA mortar. The research conclusion confirms that the best mix ratio, high gas content, and poor fluidity are the core factors affecting the technical indicators of mortar and the focus on quality control. Through this research work, a wealth of theoretical methods and practical experience data to ensure the quality and qualified indicators of mortar have been summarized, and the prevention of acute diseases (bubble and through-holes) has played a guiding role. The research result ensured the optimal quality characteristics and indexes of viscoelastic materials, and the operation of high-speed railways was safe.

The deformation evolution law and stability evaluation of the high-filled slope in the cutting hills to backfill ditches project

The cutting hills to back ditches (CHBD) project has been widely implemented since urbanization in hilly areas is steadily rising. The stability of the high-filled slope and the problem of foundation settlement deformation has become one of the vital issues for safe construction. This paper focused on the deformation evolution law and stability assessment of the high-filled deposit slope composed of the soil-rock mixture (S-RM) in the CHBD project, in Shiyan City, Hubei Province as examples. First, large-scale direct shear tests of S-RM with different rock block proportions (RBPs) under different various normal stresses were carried out, and its mechanical properties were analyzed. Next, the finite element method was used to simulate the processes of the step-by-step filling, and the deformation evolution law was analyzed. Then, the limited equilibrium method (LEM) was used to obtain the potential sliding surfaces and the corresponding safety factors of the high-filled slope, and the safety of the construction was assessed. Finally, automated monitoring of the step-by-step settlement and deep soil deformation was computerized for the typical locations, and the long-term stability of the high-filled slope was studied. The results demonstrate that the first layer of backfill in the F area contains the largest incremental settlement displacement in the y-direction, whereas the value in the G area occurs at the site of the fill layer close to the slope surface at each filling timestep. The displacement response value steadily declines with the increasing filling depth and horizontal displacement, presenting a clear spatial influence range, with the site of maximum incremental displacement as the center. After filling, the safety factors of the potential sliding surface in the F and G areas are 2.531 and 1.118, respectively, and the slope is in a stable state. The monitoring data show that the deformation mostly takes place within 10 m of the surface. The study’s findings are thought to offer technical and practical knowledge for the slope risks.

Two-dimensional chlorinated vapour intrusion model involving advective transport of vapours with a highly permeable granular layer in the vadose zone serving as the preferential pathway

Vapour intrusion (VI) is the process through which volatile organic compounds migrate from the subsurface source to the soil predominantly by diffusion, entering the overlying buildings through joints, cracks or other openings. This activity poses potentially serious health hazards for the occupants. Because of these health risks, recommendations for site closure are often made by quantifying the VI risks using mathematical models known as ‘vapour intrusion models’ (VIM). Most of these VIMs seem to overlook the role of preferred pathways like utility lines, high conductivity zones of soil or rocks, etc., which act as the path of least resistance for vapour transport thereby increasing vapour intrusion risks. This study presents a two-dimensional (2-D) chlorinated vapour intrusion (CVI) model which seeks to estimate the source-to-indoor air concentration attenuation. It takes into account the effects of a highly permeable utility line embedment as a preferential pathway. The transport of 2-D soil gas is described using the finite difference method where advection serves as the dominant transport mechanism in the preferential pathway layer, while diffusion applies to the rest of the vadose zone. The model returned results comparable with other models for the same input parameters, and was found to closely replicate the results of 3-D models. The simulations indicate that the presence of highly permeable utility line embedment and backfill layers do trigger a higher indoor air concentration compared to a no preferential pathway scenario.

Combining geophysical prospection and core drilling: Reconstruction of a Late Bronze Age copper mine at Prigglitz-Gasteil in the Eastern Alps (Austria).

Prehistoric mines are often too large and too deep for conventional archaeological excavations. Non-destructive and minimally invasive methods of prospection can help to overcome these limits. Our case study of a Late Bronze Age opencast mine (ca. 1050 to 780 BC) shows the potential of geophysical prospection methods combined with core drillings. For the reconstruction of this mine, we combined electrical resistivity and induced polarization (IP) tomography, seismic refraction tomography (SRT) and ground penetrating radar (GPR). The geophysical data were collected based on an orthogonal grid of 10 longitudinal and transverse profiles, laid out over an area of ~330 × 300 m. The profiles allowed a three-dimensional interpolation of the geological units, the mining dumps, the mining areas and the residual mineralization. Additionally, two deep cores were drilled to ground-truth the geophysical prospection results. They provided information about the stratification at intersections of the measurement grid, and this proved crucial for validating the interpreted geophysical profiles. Each geophysical method applied provided different information for the reconstruction of the site: the electrical resistivity tomography offered the best clues as to the locations of the geological units and the dumps, the seismic refraction tomography visualized the transition between the dump or backfill layers and the underlying bedrock, and the IP measurements revealed residual mineralization. The georadar measurements, on the other hand, did not contribute to the interpretation owing to the limited depth of penetration. Based on the combination of borehole and geophysical data, it was possible to develop a hypothetical model of an open-pit mine for copper ore that developed in three phases (mines A-C) during the Late Bronze Age. Without the control provided by the core drillings, one of the mining areas (mine A) could not have been correctly identified in the geophysical prospections.

Novel soil-pegged geogrid (PG) interactions in pull-out loading conditions

In current study, large-scale pull-out tests were conducted to examine the behavior of a novel reinforcement system named “Pegged Geogrid” (PG) under pull-out loading condition. Metal pegs were combined with geogrid to enhance resistance to pull-out. Incorporating pegs with geogrids alleviates bolting, welding, clamping, increasing geogrid length or making alterations to the geogrid as recommended by previous researchers. Peg roots are simply inserted/driven through apertures into the soil, nailing the geogrid to the lower and subsequently the upper backfill layers. Effects of soil particle size, normal pressure, peg length, width, and numbers has been evaluated using two sandy and a gravely soil. Results show that inclusion of pegs significantly enhances soil passive resistance contribution to pull-out. Increasing the width and number of pegs, resulted in enhancing passive soil resistance activation in front of the bearing surfaces and thus greater pull-out resistance augmented by soil particle size and normal pressure. Displacements corresponding to maximum pull-out forces gradually improved by peg width and strain distribution along geogrid in the PG system progressively became linear in contrast to the non-linear distribution in the conventional soil-geogrid (NG) system. Normal pressure was more influential on enhancing pull-out resistance in coarser soil.

Evaluation on the full-scale testbed performance of lightweight foamed soil using railroad loading system

The accumulated critical settlement usually occurs at the railway bridge approach zone due to the sudden variation in track stiffness and the difference in foundation property. This problem leads to the fast degradation of the whole track structure. Therefore, this research aims to develop a novel backfill material that helps improve the displacement resistance of the track’s supporting layer. The new flowable fill material is designed to gain the advantage of self-leveling, lightweight, and strong stress-bearing capacity through utilizing of local excavated soil, cement, and preformed foam. To cope with this objective, three full-scale testbed sections were constructed including a controlled section (conventional cement treated base), lightweight clay soil section (CL), and lightweight silty soil section (SM). Using the railroad loading system (RSL) to replicate actual trainload behaviour, a static wheel load (0-120kN) and dynamic wheel load (600,000 cyclic sinusoidal loads, 5 Hz) are applied on the surface to record the internal roadbed pressure, elastic, and plastic displacement of the backfill layer. Test results indicate significant improvement of both novel backfill materials compared to conventional cement treated base. With an average reduction for roadbed pressure and displacement of >35% on static loading, and >30% on dynamic loads. Track stiffness was also improved by up to 40% after 300,000 cyclic loads. Overall, all three sections meet the Korea roadbed design standards having a plastic settlement < 3 mm after 1 million dynamic trainloads. This promising solution can be applied in multiple regions to promote the development of sustainable railway backfill at bridge transition.

Full scale tests of various buried flexible structures under failure load

The aim of the tests described in the paper was conducting a displacement and stress analysis of four buried flexible structures made in different technologies under failure load. Generally, the laboratory tests carried out on in full scale confirms that all four culvert models of the work safely despite the reduction of the backfill layer over the structures to 0.3 m (less than according to standard recommendations) and increasing the load to 1960 -2000 kN (almost 4 times more than according to standards and recommendations). In the case of a PE plastic pipe, the main measured parameter was displacement and for other steel research models it was the stress. The obtained maximum values of these parameters were compared with the permissible standard values. Maximum displacement values were recorded in the crowns of the structures up to 12.57 mm for PE plastic pipe model. The maximum stresses for steel structures were 85.28 MPa (for corrugated steel pipe), 111.5 MPa (Box Culvert) and 447.9 MPa (Multi Plate non-circular structure). Despite the exceed stress in the case of Multi Plate structure, the steel structure did not lose its stability. The analyses carried out were aimed at determining database, which in its assumption, allows the verification of calculations performed by a numerical method such as FEM.

RESEARCH INTO DYNAMICS OF ADSORPTION OF HEAVY METALS ON ACID-ACTIVATED BENTONITE

Acid activation of bentonite clay is a common way to obtain porous adsorbents of organic and inorganic substances. Acid activation with preservation of the layered structure is the initial stage of chemical modification. Acid treatment of natural aluminosilicates is aimed at increasing their adsorption capacity and specific surface area. In industrial practice, water treatment of heavy metals is in most cases carried out bypassing the liquid through a fixed layer of backfill. Therefore, in this study, we studied the dynamics of adsorption with the definition of the main characteristics of the process: the speed of the working zone, the coefficient of protective action, the length of the working layer, the loss of protective action time, the duration of the sorption column before leakage. In addition, the establishment of the basic laws of this process can be used to determine the optimal parameters of the sorption material at a given initial characteristic — the length of the layer of the sorption column, the filtration rate.&#x0D; We have studied the possibilities of chemical modification of granular bentonite during acid-salt treatment. Through sorption columns with a height of 0.1; 0.2 and 0.3 m, filled with samples of modified bentonite, were passed model solutions of salts Fe2+, Mn2+, Cu2+ and Cd2+ with a concentration of cations of 0.01 g/dm3. The flow rate of the solution was 0.5; 1.0 and 1.5 m/h.&#x0D; Experimental data show that the optimal sorption values ​​are obtained for samples of modified bentonite: at the same height of the sorbent layer and flow rate, the duration of the layer before skipping in modified samples is 1.25—1.52 times higher than in unmodified ones. It is established that the sorption time before skipping mainly depends on the flow rate and the height of the sorbent layer. Thus, at a layer height of 0.3 m and the same rate of transmission of the solution, the sorption time is up to 3.5 times greater than at a layer height of 0.1 m for all investigated cations.

Characteristic Features of Hybrid Bridge Structure Models

This work discusses the classification of bridge structures and their models. Examples of hybrid models are also indicated in the case of homogeneous and mixed structures. Where hybrid design and model cases are presented, an algorithm for the analysis of contact interactions between subsystems is provided. The soil and shell structure is adopted as an example of analyses, where in its characteristic feature, differentiating it from classic bridges, is the large influence of both the soil backfill and the road surface as load-bearing elements of the structure. There are two structural subsystems present in the model of the soil-shell structure: a corrugated sheet coating and a soil backfill with a surface. The interaction between them is modeled as a contact interaction, i.e. forces with a direction normal and tangent to the line of the circumferential band of the shell. The paper presents an algorithm of their analysis, resulting from the outcomes of tests with the use of strain gauges, with the load being a vehicle changing its position. The advantage of the algorithm is that it takes into account the actual physical properties of the soil in the backfill layers and the contact layer of the coating with the soil. Direct contact force measurements along the entire length of the circumferential strip are very difficult. In practice, pressure gauges are used to determine normal interactions.

Construction of elastic viscoplastic constitutive model and settlement control of over-consolidated soil using finite element software ABAQUS

To study the settlement process of high-filled embankment before and after construction, an elastic viscoplastic constitutive model of over-consolidated soil is designed based on finite element analysis. The model is used to predict the settlement of subgrade before and after construction. First, the lower load surface is used as the reference yield surface of strain rate. Based on the principle of relative over stress, two rate sensitive parameters are established through the measurement of triaxial compression test with different strain rates. Second, the relative over stress function, stress function, and dynamic yield criterion function are established. Finally, two kinds of over-consolidated soils with over-consolidation ratios of 16 and 8 are tested for triaxial shear creep, and the finite element software is used for simulation analysis. The results show that the ultimate axial strain decreases with the decrease of deviatoric stress. When the creep time exceeds 3000min, the model has good prediction effect. The finite element calculation results of different backfill layers in inversion parameters show that the maximum settlement layer of high-filled embankment may not occur at the top or bottom, so attention should be paid in the construction process of high-filled embankment. This exploration provides a reference for the study of long-term deformation and strength of high-filled embankment.

Treatments to improve the aeolian sand foundation in solar park construction

The aeolian sand in the Mohammad bin Rashid Al Maktoum (MBR) Solar Park Phase IV Project site in Dubai, United Arab Emirates, is cohesionless, uniformly graded, non-plastic fine sand, with high permeability, low shear strength and low bearing capacity, which are properties that cause many geotechnical and structural challenges. With aeolian sand used as backfill soil, sandstone and sabkha (gatch, gypsum) excavated during field levelling were used as sand fixation material to improve the aeolian sand foundation. In a field compaction test, the compaction method, moisture content, paving thickness, number of rolling passes, backfill layer deformation, compaction coefficient and California bearing ratio were analysed to summarise the technological aspects of the compaction process. Rolling greatly improved the aeolian sand foundation, achieving the required capacity for various projects. The surface layer was stabilised by sandstone–gatch, which had the strongest resistance to wind erosion. By contrast, the resistance of the sandstone–gypsum layer to wind erosion was moderate, and that of the sandstone layer was weak. The experiments used to improve the aeolian foundation in this study can be applied to similar desert areas on the Arabian Peninsula and in North Africa.

Multiobjective optimization of underground power cable systems

This paper presents a modified Jaya algorithm (MJaya) for optimizing the material costs and electric-thermal performance of an Underground Power Cable System (UPCS). Three power cables arranged in flat formation are considered. Three XLPE high voltage cables are situated in the thermal backfill layer for ensuring the optimal thermal performance of the cable system. The cable backfill dimensions, cable backfill material, and cable conductor area are selected as design variables in the optimization problem. In the study, the Finite Element Method model is validated experimentally.The Particle Swarm Optimization (PSO), Jaya, and MJaya algorithms are used for multiobjective optimization in order to design a cable system in such a way to minimize the cable backfill costs and maximize the allowable electric current flowing through the cables. For the case study, calculations performed using the Jaya algorithm indicated 1.7 mln Euro cable system costs while cable ampacity is equal to I = 1460 A. The calculations are performed for the objective function values equal to w1 = 0.5 and w2 = 0.5. Such an optimization parameters set allow obtaining low costs of UPCS alongside with reasonable cable line ampacity.What is more, the results of the optimization obtained by Jaya, MJaya, and PSO algorithms are compared. Therefore, Coverage and Hypervolume metrics are incorporated. It is concluded that both the Jaya and MJaya algorithms performed better when compared to the PSO algorithm.

Assessment of Pohang Earthquake-Induced Liquefaction at Youngil-Man Port Using the UBCSAND2 Model

The practical constitutive model UBCSAND2, which combines two-mobilized planes—a maximum shear stress plane and a horizontal plane within a framework of classical plasticity approach—is used to incorporate shear-induced effects in both loading and unloading as well as principal stress rotation effects. UBCSAND2 was calibrated by capturing cyclic direct simple shear (CDSS) test results of Pohang sand, which was collected from liquefied paddy fields due to the 2017 Pohang earthquake (Mw = 5.4) in South Korea. The model procedure focuses on simple shear condition because it best simulates field conditions under earthquake loading. The calibrated UBCSAND2 model is then used to assess the liquefaction-induced damages that occurred at the quay wall and backfill layer in Youngil-man port near the epicenter of the Pohang earthquake. The numerical results show that liquefaction mostly occurred in silty sand layers, in which the excess pore pressure ratio reached almost one. The estimated displacements of the quay wall and the predicted settlement of reclaimed area obtained from the analysis were in good agreement with those obtained from field measurements.

Interference of torsion waves in the underground pipeline caused by the movement of the damaged foundation

In this article, we study the strength of underground pipelines, which are operated in difficult mining and geological conditions in area full of tectonic faults. In such seismically active areas, in addition to the pressure load of the transportedproduct, the pipe is subjected to additional effects from the movements of the damaged foundation. When the movements are transient,a dynamic analysis of the behavior of structures must be carried out. The aim of the study is to develop a model to describe the non-stationary process of deformation of the pipeline on the damaged foundation, caused by the sudden mutual reversal of several fragments of the base around the axis of the pipe. The dynamics of the pipeline was investigated in a linear setting, modeling it with an infinite tubular rod. We consider blocks of a basis to be absolutely rigid; the behavior of a thin layer of soil backfill is described with the help of Winkler's hypothesis. The kinematics of mutual rotations of the base fragments is given by discontinuous functions from the axial coordinate. The strength of the pipeline is assessed by summing the standard and non-standard stresses, while the pipe is considered a torque-free shell. This approach makes it possible to assess the strength of the underground pipeline not by the external load from the soil, which is usually unknown, but by the kinematic parameters of the movements of the fault banks. An initial-boundary value problem for the differential equation of torsion with a discontinuous right-hand side has been formulated. Based on the analytical solution of the problem, the influence of the interference of torsion waves excited by sudden reversals of the foundation fragments around the axis of the pipe on the stress state of the pipeline under pressure has been studied. It has been established that the dynamic effects significantly depend on the structure of the breaking movements of the foundation and on the distance between the faults.

Coupled TDA–Geocell Stress-Bridging System for Buried Corrugated Metal Pipes

The interaction between surface structures and buried pipes is unavoidable. For instance, placing the pipe at a shallow depth, near to the surface, attracts substantial additional earth pressures due to the external surface loading, causing overstressing or unacceptable deformations of the buried pipe. Several alternatives may be used to mitigate this situation, including using induced trench construction, using lightweight fill material to reduce imposed loads, and finally relocation of the pipe, which is the most expensive and least desirable alternative. The characteristics of the used backfill material control the pipe–soil interaction mechanism and thus the amount of exerted pressures. Using lightweight compressible materials, such as tire-derived aggregates (TDA), above buried pipes has long been investigated to reduce pipe stress. However, such materials may result in undesirable surface settlement that may compromise the pipe performance. In this paper, a coupled TDA–geocell stress-bridging system was developed utilizing six full-scale tests and a comprehensive three-dimensional (3D) finite-element modeling component. The developed system uses a geocell-reinforced top granular backfill layer over the TDA layer to induce a stress-arching mechanism capable of reducing the imposed stresses on the pipe below and control the surface settlement.