Clay Ground Research Articles

Thermo-hydro-mechanical behaviour of energy tunnel in unsaturated soils

Soils surrounding energy tunnels are often unsaturated, particularly in areas with a low water table. All studies of the mechanical behaviour of energy tunnels focused on saturated or dry soils. Through numerical simulations using a coupled thermo-hydro-mechanical model for unsaturated soils, this study aims to improve the understanding of the interactions between energy tunnels and unsaturated ground. The influences of water table position and soil type on the mechanical behaviour of energy tunnels were investigated. Results show that the thermally-induced lining convergence of energy tunnels does not change much with the water table position. Nevertheless, the other mechanical responses (e.g., settlements of ground and tunnel and lining stress changes) highly depend on the water table position. These mechanical responses are more significant when the water table is higher than the tunnel center, except for the larger settlements at a lower water table in clay. Furthermore, the above responses are underestimated if soils above the water table are assumed to be completely dry. The degree of underestimation is most significant for the clay, followed by silt and sand, e.g., a maximum of 54%, 23% and 10% in the change of circumferential stress, respectively. These results highlight that the unsaturated soil model should be used to evaluate the thermo-hydro-mechanical responses of energy tunnels in unsaturated soils, particularly for the clay ground.

Reinforcement of soft clay using industrial residue-based soil stabilizer and recycled fine aggregate: A comprehensive investigation

This study aims to assess the effectiveness of an industrial residue-based soil stabilizer (GDP) and recycled fine aggregate (RFA) in enhancing the properties of soft clay. The GDP is composed of ground granulated blast furnace slag (GGBS), desulfurized gypsum (DG), and Portland cement (PC). The optimal formula for GDP and the appropriate amount of RFA needed to reinforce the soft clay were determined through unconfined compressive strength (UCS) testing. The microscopic characteristics and reinforcement mechanism of the GDP-RFA-reinforced soft clay were then analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetry (TG), and scanning electron microscopy (SEM) techniques. The effectiveness of utilizing GDP and RFA as reinforcement additives in soft clay ground was also validated through field testing. The experiments showed that using GDP instead of cement significantly increased the strength of soft clay, with the optimal mass ratio of GGBS, DG, and PC in GDP being 6:1:3. The strength of the GDP-reinforced sample initially increased and then decreased as the RFA content increased, reaching its peak at a RFA content of 30 %. The formation of C-S-H and C-A-H gels, along with AFt crystals, in the GDP-RFA-reinforced sample greatly enhanced its mechanical properties. RFA helped to form more hydrated products and provide effective mechanical support, but excessive RFA could lead to large pores in the matrix. The use of GDP and RFA in reinforcing soft clay ground significantly improved its specific penetration resistance, bearing capacity, and compressive modulus. A significant linear correlation was found between the compressive modulus of reinforced clay and its specific penetration resistance or UCS. As a result, an empirical model has been developed to predict the compressive modulus of reinforced clay based on this correlation.

Soil conditioning of clay based on interface adhesion mechanism: Microscopic simulation and laboratory experiment

Clogging frequently occurs in the cutter head, excavation chamber or screw conveyor when an earth pressure balance (EPB) shield machine is tunneling in soft or silty clay ground with high clay mineral content. In this paper, montmorillonite, kaolinite, and illite were selected as research objects, and molecular dynamics simulation and laboratory experiment were adopted. At the microscopic scale, dynamic contact behavior and interfacial mechanical behavior of the interface between clay minerals and water/surfactant solution was simulated and the interfacial adhesion and conditioning mechanism between clay minerals and water/surfactant solution was revealed. Thus, sodium dodecyl benzene sulfonate surfactant was selected as the main composition of the soil conditioner. Then, the adhesion stress before and after soil conditioning and the contact angles between clay minerals and water/surfactant solution were tested and analyzed at the macroscopic scale. The result shows that the contact angle between droplet and clay mineral surface is an important parameter to characterize soil adhesion. The simulation rules of the microscopic contact angle are consistent with the experiment results. Furthermore, the adsorption energy between microscopic substances is dominated by electrostatic force, which can reflect the adhesion stress between macroscopic substances. Soil adhesion stress can be effectively decreased by adding the surfactant to the soil conditioner.

Degradation of straw-based wick drain and its effect on consolidation

The recycling of straw, a type of agricultural waste in a large volume, has considerable attention, and attempts have been made to fabricate straw-based wick drains in soft clay ground improvement. Although it has low carbon emissions and is environmentally friendly, the biodegradation process of wick drains and its effect on consolidation need to be further investigated. In this study, the biodegradation process was examined by subjecting straw and plastic wick drains to degradation tests in soils from the prototypical project for comparison. The results show that the degradation of straw wick drains exhibits a decrease in the discharge capacity and tensile strength, and the degradation percentage of both exceeds by 30% after 240 days, whereas the mass loss is only 10%. After degradation, the abundance of cellulose-degrading bacteria increases by 3–10%, respectively. The biodegradable behavior of straw wick drains is achieved by the rapid community succession of multiple degrading bacteria and the population growth of cellulose-degrading bacteria. Afterwards, the theoretical calculation model considering the drain degradation was performed to understand the consolidation procedure, suggesting the effective substitution of straw wick drains.

The Experimental Analysis Of The Effect Of Geotextile Reinforcement Of Cohesive Soil On The Settlement And Bearing Capacity

The properties of the soils in terms of engineering must be identified for the design of buildings and foundations to be constructed in areas where soft clay or loose sand ground conditions predominate. The engineering properties of different soils diversify in a broad range based on the sort of the ground in addition to the terrain conditions like the degree of compaction, water content, consolidation pressure, loading, and drainage conditions. Grounds may not perpetually hold the desired properties. Thanks to the structures to be built on the grounds, excessive settlements or collapses can happen because of inadequate ground bearing capacity. In order to reinforce the weaknesses of the soils, either the application of a deep foundation should be employed, or a proper improvement method should be applied to the foundation ground.In the study, the effect of the reinforcement of the geotextile, which has become widespread, on the clay ground was examined. Experiments have been conducted to identify the index properties, settlement, and sliding resistance parameters of soils on Süleyman Demirel University Soil Mechanics Laboratory on clay samples from the provinces of İzmir and İstanbul. Following the identification of the settlement and sliding values, the geotextile was added, and its effect on the settlement and bearing strength values was analyzed. Experiments were conducted by placing single-layered and double-layered geotextile in the samples with the values of optimum water content, the water content 10% more than the optimum value, and the water content 10% less than the optimum value.The results achieved after laboratory experiments are displayed with graphics and compared with each other.

Rheological consolidation analysis of saturated clay ground under cyclic loading based on the fractional order Kelvin model

AbstractBased on Biot porous medium theory, considering the coupled reaction of soil skeleton rheology and pore pressure dissipation, the present work investigates the dynamic consolidation characteristics of saturated clay ground under cyclic loading. First, the rheological behavior of the soil skeleton was described by the fractional order Kelvin model. The dynamic consolidation governing equations for the saturated clay were established theoretically in a three‐dimensional axisymmetric coordinate system. Second, the transform domain analytical solution of the dynamic consolidation of saturated clay was obtained using the Hankel–Laplace coupled transform method, and the solution in the time–space domain was further obtained through numerical inversion. Finally, the rheological consolidation behavior of saturated clay under cyclic loading and the influences of parameters were analyzed. The results show that the rheology of the soil skeleton had an inhibitory effect on pore water permeability; compared with elastic skeleton soil, the rheological clay had a slower settlement rate in the primary consolidation stage, a faster rate in the secondary consolidation stage, and greater long‐term settlement. In addition, under cyclic loading, the pore pressure response in saturated clay lags behind the effective stress, and a larger viscous order is associated with faster development of cumulative settlement.

Soil disturbance evaluation of soft clay based on stress-normalized small-strain stiffness

Soil disturbance includes the change of stress state and the damage of soil structure. The field testing indices reflect the combined effect of both changes and it is difficult to identify the soil structure disturbance directly from these indices. In the present study, the small-strain shear modulus is used to characterize soil structure disturbance by normalizing the effective stress and void ratio based on Hardin equation. The procedure for evaluating soil sampling disturbance in the field and the further disturbance during the subsequent consolidation process in laboratory test is proposed, and then validated by a case study of soft clay ground. Downhole seismic testing in the field, portable piezoelectric bender elements for the drilled sample and bender elements in triaxial apparatus for the consolidated sample were used to monitor the shear wave velocity of the soil from intact to disturbed and even remolded states. It is found that soil sampling disturbance degree by conventional thin-wall sampler is about 30% according to the proposed procedure, which is slightly higher than that from the modified volume compression method proposed by Hong and Onitsuka (1998). And the additional soil disturbance induced by consolidation in laboratory could reach about 50% when the consolidation pressure is far beyond the structural yield stress, and it follows the plastic volumetric strain quite well.

Comprehensive Experimental Investigation of Improved Clay Ground by Sand Compaction Pile Varying from Low to High Area Replacement Ratios

Comprehensive Experimental Investigation of Improved Clay Ground by Sand Compaction Pile Varying from Low to High Area Replacement Ratios

Model test and numerical simulation of a new prefabricated double-row piles retaining system in silty clay ground

This paper introduces a new prefabricated recyclable double-row piles retaining system for excavations in silty clay ground. Laboratory model test and numerical simulation are conducted to study the system behavior upon excavation. The horizontal displacement (δh), Von Mises stress (σM), strain (ε), ground surface settlement (δv), and earth pressure are systematically investigated. Furthermore, the monitoring data of 13 excavation cases supported by double-row piles retaining system are presented and discussed. The experimental results can basically match the numerical results, and the maximum σM, maximum bending moment (Mmax), maximum horizontal displacement (δhm) of structural members are all less than the tolerance limits. The ground surface settlement model of double-row piles retaining system consists of three zones, i.e., rebound influence zone, primary influence zone and secondary influence zone. The δhm values are 0.07%–1.42% of the excavation depth (He). The maximum ground surface settlement (δvm) is generally less than δhm. The ratio of δvm/δhm varies between 0.09 and 0.76, with an average value of 0.5. The observed earth pressure on the retained side of front pile (paf) is about 0.53–0.57 γH below the excavation surface. Above the excavation surface, paf decreases dramatically when getting closer to the ground surface.

Comparative analysis on effectiveness of crushed aggregate and scoria gravel as columnar reinforcement material under raft foundation

Scoria gravel is widely used as stabilizer material in road construction and concrete works. However, limited information regarding its performance as columnar stabilizing material has been reported. This study hence explores suitability of scoria gravel as columnar stabilizing material in compressible soils. Besides, comparative analysis to evaluate effectiveness of crushed aggregate columns (CAC) and scoria gravel columns (SGC) in improving deformation characteristics of clay ground was carried out by using finite element based numerical analysis. Compressible massive clay reinforced with CAC and SGC under building load was modeled to simulate the settlement attributes of the foundation material. The conducted numerical model considered both the floating and end bearing gravel columns. Finding of the study revealed that provision of floating SGC performs better than the crushed aggregate stone column in lessening vertical deformation of the clay foundation. However, the floating SGC did not result in significant improvement in lessening lateral deformation in comparison with group of CAC. Hence, application of granular piles as columnar reinforcing material in purely clay soil is not as effective as SGC from settlement reduction view point. Contrarily, the bridging effect of end bearing crushed aggregate pile is more pronounced than that of scoria gravel as the column material directly gets contact with stiff substratum. It can also be inferred from finding of the study that application of granular pile group suits well compressible grounds where stiffer strata is situated immediately at column tip.

Evaluation of CAMEL over the Taklimakan Desert Using Field Observations

Infrared (IR) land surface emissivity (LSE) plays an important role in numerical weather prediction (NWP) models through the satellite radiance assimilation. However, due to the large uncertainties in LSE over the desert, many land-surface sensitive channels of satellite IR sensors are not assimilated. This calls for further assessments of the quality of satellite-retrieved LSE in these desert regions. A set of LSE observations were made from field experiments conducted on 16–18 October 2013 along a south/north desert road in the Taklimakan Desert (TD), China. The observed LSEs (EOBS) are thus used in this study as the reference values to evaluate the quality of Combined ASTER MODIS Emissivity over Land (CAMEL) data. Analysis of these data shows four main results. First, the CAMEL datasets appear to sufficiently capture the spatial variations in LSE from the oasis to the hinterland of the TD (this is especially the case in the quartz reststrahlen band). From site 1 at the southern edge of the Taklimakan Desert to site 10 at the northern edge, the measured LSE and the corresponding CAMEL observation in the quartz reststrahlen band first decrease and reach their minimum around sites 4–6 in the hinterland of the Taklimakan Desert. Then, the LSE increases gradually and finally reaches its maximum at site 10, which has a clay ground surface, showing that the LSE is higher at the edges of the desert and lower in the center. Second, the CAMEL values at 11.3 μm have a zonal distribution characterized by a northeast–southwest strike, though such an artifact might have been introduced by ASTER LSE data during the merging process that created the CAMEL dataset. Third, the unrealistic variation of the original EOBS can be filtered out with useful signals, as identified by the first six principal components of the PCA conducted on the laboratory-measured hyperspectral emissivity spectra (ELAB). Fourth, the CAMEL results correlate well with the measured LSE at the 10 observation sites, with the observed LSE being slightly smaller than the CAMEL values in general.

Finite Element Method of the Influence Evaluation of the Percentage of Fine Particles of Marine Clay at the Different Depth Variations to the Total Volumetric Strain of the Soft Clay Ground

Finite element method of the influence evaluation of the percentage of fine particles of marine clay at the different depth variations to the total volumetric strain of the soft clay ground is determined by the Viet Nam standard TCVN 4196:2012; TCVN 4102:2012; TCVN 4197:2012; TCVN 4199:2012. Results show clearly the percentage of the fine clay particle and the total volumetric strain (ε) with depths. The minimum value of 12% and 0.00002617 at 19.3m depth; whereas the maximum value of 38% and 0.00002609 at 25.3m depth. Moreover, a consideration of the relationship between Internal friction angle, Cohesive force, Water content, Saturation, Porosity, Viscosity, and Plasticity index with depths. Results show remarkably the increasing of the depths as the variations of the percentage of fine particles of marine clay and cohesive force, viscosity, water content, and porosity; compared with the decrease of the plasticity and internal friction angle. It is easy to conclude that the total volumetric strain of the soft clay ground is a stable and safe state to use and design the building, construction, and reference of engineers, geologists, scientists, and so on in the future.

Theoretical Evaluation for Soil Thrust of Single-Track System over Clay Slope via Upper Bound Analysis

This study aimed to theoretically evaluate soil thrust on a clay slope as a reaction force associated with the motion of an off-road tracked vehicle. The existing concept of the potential failure modes of a clay block on flat ground has extended to determine the soil thrust of sloped clay ground. Based on the upper-bound limit analysis, the soil thrust under the most critical failure was derived for three potential failure modes: block, triangular-wedge, and trapezoidal-wedge failures. Specifically, the influence of the slope angle, the shear strength of clay, the weight of a vehicle, and the geometry of a track system on the soil thrust was investigated. Only the block and triangular wedge failure modes were able to occur, and the geometry of a single-track system could lead to different failure modes. Under the block failure mode, the soil thrust decreased as the slope became stiff, and the vehicle weight increased. On the other hand, the soil thrust decreased as the slope angle decreased under the triangular-wedge failure mode.

Evaluating the Effectiveness of Nonwoven Geotextile-Encased Cinder Gravel Column in Improving Load-Bearing and Deformation Characteristics of Soft Clay

Application of vertically installed columnar materials made of natural gravels or crushed aggregate is one of the commonly implemented practices to improve the performance of soft clay grounds under footing load. Alternative materials like cinder gravel also plays a reinforcing role when blended with soft clay. However, information on the precise extent to which a vertically installed cinder gravel column is effective in improving the properties of a clay foundation and its potential response to the permanently applied footing load has not been well documented in the literature. Hence, the current study specifically aimed at evaluating the effectiveness of geotextile-encased cinder gravel column in improving deformation and bearing capacity of soft clay ground. The experimental model which considered installation of a single geotextile-encased cinder gravel column into soft clay was considered. A cylindrical steel container was used in designing the experimental test. The container was filled with clay soil and the cinder gravel column was vertically installed through a replacement method. Finding of the study revealed that ultimate load-bearing capacity of the soft clay foundation after being reinforced with conventional cinder gravel was 1.85 times that of the untreated soft clay soil. The load-carrying capacity of the clay soil decreased with increment in diameter of the column whereas it is directly related to the volume replacement ratio. With regard to directional improvement, the vertical reinforcement performs better than the horizontal geotextile strips in cinder gravel column from bearing capacity improvement view point. In lessening settlement, however, application of horizontal geotextile discs at spacing ranging between half- and full-column diameter overweighs performance of the vertical encasement. In summary, application of geotextile encasement to the top 75% of the clay thickness is sufficient to come up with optimum improvement in bearing capacity and encasing the entire thickness is not necessarily required.

Large-Scale Pile Load Tests in Mixed Sand and Soft Clay Ground: Impact of Aging and Stops in Driving

Large-Scale Pile Load Tests in Mixed Sand and Soft Clay Ground: Impact of Aging and Stops in Driving

Upper-bound solutions for the soil thrust of clay under a track system in 3D conditions

This study proposes a quick and reliable method for estimating the soil thrust in clay ground for a tracked vehicle based on limit analysis in three-dimensional conditions. With respect to the shape and location of failure surfaces in clayey ground, block, triangular wedge, and trapezoidal wedge failure modes were considered. Between the upper-bound solutions from the different failure modes, the least upper-bound solution was proposed as the soil thrust. To verify the proposed solution, it was compared to the model test and numerical simulations for a track system over model clay ground. The proposed upper-bound solution is expected to produce a reliable soil thrust quickly in real time, especially for submerged heavy-weight remotely operated vehicles (ROVs).

Evaluation of a Long-Term Thermal Load on the Sealing Characteristics of Potential Sediments for a Deep Radioactive Waste Disposal

An in situ and a batch heating experiment were applied on the fine-grained sediments of the Opalinus Clay from Mont Terri (Switzerland) and the Boom Clay of Mol (Belgium), both being currently studied as potential host formations for deep nuclear waste disposal. The purpose was here to test the impact of a 100 °C temperature rise that is expected to be produced by nuclear waste in deep repositories. The experiment on the Opalinus Clay mimicked real conditions with 8-months operating heating devices stored in core drillings into the rock. The comparison of the major, trace, rare-earth elemental contents and of the whole-rock K-Ar data before and after heating shows only a few variations beyond analytical uncertainty. However, the necessary drillings for collecting control samples after the experiment added an unexpected uncertainty to the analyses due to the natural heterogeneity of the rock formation, even if very limited. To overcome this aspect, Boom Clay ground material was subjected to a batch experiment in sealed containers during several years. The drawback being here the fact that controls were limited with, however, similar reproducible results that also suggest limited elemental transfers from rock size into that of the <2 μm material, unless the whole rocks lost more elements than the fine fractions. The analyses generated by the two experiments point to identical conclusions: a visible degassing and dewatering of the minerals that did not induce a visible alteration/degradation of the host-rock safety characteristics after the short-term temperature increase.

Consolidation effect of prefabricated radiant drain vacuum preloading technology: A physical model case study

The large amount of dredged soil produced annually by rivers, lakes, seas, and oceans affects the ecological environment. Dredged material such as soft clay, which has high fluidity and high water content, is often utilized for building ground in engineering practice. Conventional vacuum preloading can effectively treat such soil but has a deprived consolidation effect. To improve the treatment effect, in this study, prefabricated radiant drain (PRD) vacuum preloading technology is proposed innovatively by adding prefabricated horizontal drains (PHDs) based on a prefabricated vertical drain (PVD). And a four-way connector is designed to connect PVD and PHDs, PHDs are attached to PVD to transmit vacuum pressure. A series of laboratory tests are run to compare and analyze the differences between conventional PVD and PRD vacuum preloading. The water discharge, average surface settlement, water content, and undrained shear strength values are analyzed. Then the parametric analysis of PHD spacings and length-width ratios (characterizing PHD length) are investigated. Overall, with the new PRD method, the consolidation effect of soft clay ground with a water content of 80% is improved by approximately 15%.

Modeling heat and mass transfer during artificial ground freezing considering the influence of water seepage

In the system of artificial ground freezing under water seepage, the dynamic liquid–ice phase equilibrium relationship considering the contribution of water seepage pressure was established based on the classical thermodynamics fundamentals. The freezing characteristic function was represented by combining the Young–Laplace law with van Genuchten model. A thermal-hydraulic model of saturated porous media considering dynamic liquid–ice phase equilibrium was established and validated thorough laboratory tests under various seepage velocities. The temperature field evolution laws of sand, silty and clay grounds were studied based on the thermal-hydraulic model. The temperature field development laws of primary side tunnel of subway cross passages in silty-clay layer were analyzed by applying the thermal-hydraulic model. The relationship between water seepage pressure and the decrease of water freezing point temperature was obtained according to the dynamic liquid–ice phase equilibrium. Compared with the simulation results of considering static liquid–ice phase equilibrium relationship, considering the dynamic liquid–ice phase equilibrium relationship changes the distribution of water-ice phase transition front and has significant influence on the temperature evolution in silty ground. However, that influence in sand ground and clay ground is insignificant because of the relatively lower water seepage pressure in sand ground and poor thermal conductivity in clay ground. Due to the cold energy accumulation bring by water seepage, the freezing rate in the downstream of freezing pipes is faster than that in the upstream of freezing pipes. This effects are exacerbated by lower decrease of water freezing point temperature caused by minor water seepage pressure in the downstream of freezing pipes. Four representative temperature measured points were selected to acquire the relationship between simulation and on-site temperatures. It was observed that the trends of simulation results reflect the tunnel freezing process well.

Three (3D) dimension model of settlement differences of the clay ground under rigid foundation by the affection of the groundwater variations – A comparison

In recent decades, settlement differences of the Clay ground implemented in areas and countries in the world. Whereas marine clay ground behaviors under Rigid foundation to build the construction on the clay ground with marine clay origin was evaluated the different methods such as Field and experimental measuring method, Finite Element method, formulas or TERZAGHI method and so on. Moreover, the influence of the groundwater levels is one of the most quite important problems to be needed considering. The object of this paper uses Standard Penetration (SPT), Unconfined Compression Test, and TERZAGHI formula, groundwater effects, and simulation by the software for measuring the vertical displacement (or settlement differences) of the rigid foundation on marine clay origin ground at Vinh Quang ward, Rach Gia town, Viet Nam. Results of the paper described clearly for settlement differences (vertical displacement) of the Rigid foundation as building loading with a comparison between Field, experimental, and software simulation so it can consult effectively for design and doing construction works in Civil and Geology Engineering.