Ground Stability Research Articles

The Bearing Capacity Analysis of Deep Foundation based on In-situ Dynamic Penetration Test Compared to Pile Driving Analyzer (PDA)

On road/ bridge construction, foundation stability analysis is carried out by reviewing the bearing capacity. At the planning stage, this aspect can be calculated based on empirical and numerical methods using In-situ Dynamic Penetration Test data. Meanwhile, at the implementation stage, the bearing capacity results are checked using Pile Driving Analyzer (PDA). Hereinafter, the bearing capacity result in the field is compared with the bearing capacity result at the planning stage whether they are appropriate or not. In this study, the results of bearing capacity based on empirical using Meyerhoff and Schmertmann and numerical methods using MIDAS GTS NX were compared with the results of the PDA test. This study takes an overview of the Semarang – Demak Toll Road Development Project Package 2 STA 16 + 075. The analysis was carried out based on three STA points. The results obtained show that the largest deviation value is when the PDA result is compared with the Schmertmann method, which is 0.59 and the smallest deviation is when comparing PDA with MIDAS 0.03. Both deviations are located on P 133F STA 16+711. This different deviation is due to the ultimate bearing capacity analysis based on empirical equations that only analyze single piles based on the original soil properties, while the MIDAS analysis also considers pile parameters and interface parameters. Moreover, in the PDA test, there are factors of environmental conditions.

Sensitivity analysis of influencing factors of pile foundation stability based on field experiment

Based on the finite element analysis software ABAQUS, this paper establishes a three-dimensional finite element simulation model. According to the measured data of a project in Qingdao, the settlement obtained by static load test is selected as the index to measure the stability of the pile foundation. The Poisson ratio, elastic modulus, angle of internal friction, and friction coefficient of the pile-soil contact surface of each layer of soil are selected as the factors affecting the stability of the pile foundation. The experimental results of settlement at all levels are analyzed and compared through the variable control and orthogonal experiment. Finally, the main factors affecting the stability of the pile foundation are determined as follows: the elastic modulus, Poisson ratio, friction coefficient, angle of internal friction of pile end soil, and the elastic modulus of the fourth layer of soil, which provides a specific reference value for the subsequent research on the stability of pile foundation.

Terzaghi's three stability factors for pipeline burst-related ground stability

A recent study on active trapdoor stability has been completed by the authors using Terzaghi's three stability factors approach. It was concluded that the superposition approach is an effective way to evaluate the stability of cohesive-frictional soils. This technical note aims to extend the previous active trapdoor study to perform a stability assessment of a passive planar trapdoor (i.e., a blowout condition) in cohesive-frictional soil. Note that this passive trapdoor problem represents the blowout stability of soils due to defective pipelines under high water main pressures, in spite of the frequent media news about the water main bursts which enlightens the relevance of the problem. Numerical solutions of upper and lower bound finite element limit analyses are presented in form of the three stability factors (Fc, Fs, and Fγ), which consider the effect of cohesion, surcharge, and soil unit weight respectively. In the event of passive trapdoor stability, this technique can be used to determine a critical blowout pressure due to a water mains leak. The study continues with a series of sensitivity analyses with a widely selected range of parameters including the cover-depth ratio (H/B) and the drained frictional angle (ϕ). The influence of these parameters on the three stability factors is discussed, and a practical example of adapting these approaches is also introduced. All numerical results are provided in the forms of design charts and tables that can be efficiently used with confidence in design practice.

Modification of a Constitutive Model for Gassy Clay

Gassy clays containing large, discrete gas bubbles are widely spread in deposits in shallow waters. The existence of gas bubbles may impair the original soil structure, resulting in the instability of offshore foundations and the occurrence of submarine landslides. Although gassy clay was found to exhibit different undrained shear behaviors with variations of the initial pore water pressures and initial gas volume fractions, more experimental studies and theoretical interpretations of the relationship between the effective confining pressure and undrained responses are required. A series of undrained triaxial compression tests is conducted to compare the responses of reconstituted gassy and saturated specimens at an effective confining pressure of 200, 400, or 600 kPa. An existing elastoplastic constitutive model based on the critical state is improved by updating its stress-dilatancy function and yield surface. The dilatancy equation proposed has the potential to quantify the effect of gas bubbles on the dilatancy of the soil matrix. The yield surfaces are reproduced reasonably well by optimizing the expressions of shape parameters under a variety of effective confining pressures. The model developed can describe the stress-dilatancy and stress-strain responses of both the gassy and saturated specimens.

The Stability Analysis of the Bored Pile Foundation as Liquefaction Hazard Mitigation at the University of Tadulako Reconstruction Project

A Pile foundation is one of the most important structural elements. Pile foundations are used to support buildings when the hard soil layer is located very deep to keep the structure stable and standing when loaded by internal and external forces. The University of Tadulako is located in a moderate liquefaction-prone zone. In planning for rebuilding post-earthquake, where this area suffered massive damage, it was built on loose sandy soil with shallow groundwater levels. As a result, it has a possibility of liquefaction hazards in this area. This study aims to analyze the stability of the bored pile foundation as liquefaction hazard mitigation under service and extreme conditions. The analysis is carried out using two approaches, analytical method and computer-aided numerical simulation using RSPile and GEO5 2019. The type of foundation plan that will be used is the bored pile foundation with a diameter of 0.6 meters with a depth of 10 to 13 meters. The result shows the foundation remains stable under service conditions, but under extreme conditions, the foundation collapsed for type P1.B, and recommended redesign becomes type P1.A. However, after redesigning, the foundation becomes inefficient, and further research is needed on efficient foundation design.

Load-Settlement Characteristics of Stone Column Reinforced Soft Marine Clay Deposit: Combined Field and Numerical Studies

Foundations supporting infrastructure built on soft and compressible marine soil are unlikely to sustain due to possibility of undrained shear failure or excessive settlement of the supporting soil. This necessitates the importance of implementing an adequate ground improvement strategy. Among different techniques, soft soil reinforcing by the installation of stone columns is one of the most successful methods in terms of long-term stability of foundations. To investigate the load-settlement characteristics of such reinforced soil, a group of closely spaced stone columns was constructed at a location along the eastern coast of Australia. The site geology revealed thick layers of soft, compressible marine clay deposit. These stone columns were loaded by constructing earthen embankment and the resulting load-settlement characteristics were measured by an array of sensors. A two-dimensional plane strain analysis was performed using finite element modeling simulations. Comparison of numerical results with the field data demonstrated accuracy of the numerical model. Additional studies were carried out to investigate the efficiency of the model. This paper integrates the new findings from the full-scale field study and advanced numerical simulations while drawing pertinent conclusions.

Using a blend of cement and waste glass powder to improve the properties of clayey soil

Adopting an appropriate soil stabilization technique is necessary since weak soil can lead to foundation instability and reduce a structure's life. Selecting the appropriate admixtures is very frequent among the various soil stabilization methods. This study scrutinized the feasibility of employing a blend of cement and waste glass powder (WGP) to improve the properties of clayey soil, which was classified as clay with intermediate plasticity according to the Indian Standard Soil Classification System (ISSCS). Using WGP in soil stabilization is a promising way to prevent its disposal in landfills, which may pose a severe environmental threat. In addition, using WGP can reduce the need for conventional binders like lime and cement. As a result, reducing carbon emissions will lead to sustainable development. For this purpose, crushed waste glass from waste glass production was used. A blend of 5% fixed proportion of cement and 2.5, 5, 7.5, and 10% of WGP was mixed with the soil sample. Atterberg limits, Proctor's compaction, and California bearing ratio (CBR.) tests were executed on untreated and treated soil samples. According to the test results, incorporating a blend of cement and WGP in clayey soil reduced its liquid limit and plasticity index. The plasticity index of the soil sample was decreased by 50% when a blend of 5% cement and 5% WGP was added to the soil sample. In other words, as per the ISSCS, clay with intermediate plasticity (CI) was changed to clay with low plasticity (CL) after using a combination of 5% cement and 5% WGP. Maximum dry density increased, whereas optimum moisture content decreased as the soil sample was modified using a cement blend and WGP. After adding 5% cement and 10% WGP, the maximum dry density of the soil sample was increased by 6%, and the optimum moisture content was reduced by 3%. The improvement in CBR. was significant after the soil treatment with a blend of cement and WGP. The CBR. of the treated soil was increased by 260% when a combination of 5% cement and 5% WGP was used.

Combining ground stability investigation with exploratory drilling for mine water geothermal energy development; lessons from exploration and monitoring

Mine water geothermal energy's potential for decarbonization of heating and cooling in the UK has led to increased national interest and development of new projects. In this study, mine water geothermal exploration has been coupled with ground investigation techniques to assess ground stability alongside seasonal mine water hydrogeology and geochemistry. Drilling operations in late 2020 at Dollar Colliery, Clackmannanshire, Scotland, encountered mined coal seams with varying conditions (void, intact, waste, etc.), reflecting different techniques used throughout a protracted mining history. We found that time and resources spent grouting casing through worked mine seams (ensuring hydraulic separation) can be saved by accessing deeper seams where those above are unworked. Continued assessment of existing water discharges and completion of boreholes with slotted liners into mined coal seams and fractured roof strata allowed chemical and water level changes to be monitored across a 1 year period. Mine water heads and mine discharge flow rates vary seasonally and are elevated between late autumn and early spring. The mine water has a low dissolved solute content. Dissolved sulfate- 34 S isotope data suggest increased pyrite oxidation during lower water levels. These findings can inform future building decisions, whereby housing developments on site could use the mine water for heating. Supplementary material: Borehole data and completion diagrams are available at https://doi.org/10.6084/m9.figshare.22188801 Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/topic/collections/early-career-research

Preparation of anti-washout cement-stabilized marine soft clay for scouring protection of wind power pile foundations

This study aims to prepare an anti-washout grout using marine soft clay to stabilize the wind power pile foundations. The cement, hydroxypropyl-methyl cellulose ether (HPMC), and sodium silicate were chosen as the main materials to modify the marine soft clay, and the fluidity, bleeding rate, setting time, rheology, anti-washout characteristics, and compressive strength were investigated. The results showed that high cement content, HPMC, and sodium silicate decreased the workability of grout while enhancing the washout resistance. The addition of HPMC and sodium silicate would increase the yield stress and plastic viscosity of the grout. The sodium silicate content was the key factor influencing the early strength, while the cement content and HPMC affect the later strength. The microstructures including the morphology of C-S-H gels and the content of ettringite and calcium hydroxide significantly changed with the addition of sodium silicate, and Friedel’s salt was observed through the microstructure analysis. This study can provide effective guidance for the utilization of marine soft clay, the preparation of anti-washout grout, and the control of pile foundation stability.

Predictive strength model of cement-treated fine-grained soils using key parameters: Consideration of the total water/cement and soil/cement ratios

Soil stabilization techniques have been widely used to improve the mechanical and engineering properties of soft ground, such as strength, compressibility, and permeability. Recently, dredged soils that have high water content, high compressibility, and low strength have been mixed with cement and used as filling and landfill materials. The water and cement contents and soil types (clay or silt) in these soil–cement mixtures can be determined according to the purpose of use. To this end, the design of these mixtures requires the accurate prediction of the unconfined compressive strength (qu). Therefore, this paper proposes a predictive model for qu of cement-treated fine-grained soils (CTFSs) for ground improvement and stabilization of dredged soils. Ordinary Portland cement and two types of fine-grained soils (clay and silt) were used as the basic materials in the experiment. Unconfined compression tests were performed in a wide range of experiment conditions: water content (wt: 40–170 %), cement content (c: 5–25 %), and curing time (t: 3–90 d), and the results were correlated by two key parameters, wt/c (total water content/cement ratio) and s/c (soil/cement ratio). The results demonstrated that wt/c and s/c were strongly correlated with the qu development of CTFSs depending on the curing period. Therefore, we established a predictive model for qu by combining the power and exponential functions for (s/c)X and (wt/c)Y. The X and Y values of proposed model could equally be applied for different curing periods for soils of different types with different characteristics. In addition, the proposed model could predict long-term qu by using the time coefficient (ct) normalized by the curing period of 7 d. The mean absolute percentage error and coefficient of determination of the proposed model were lower and higher, respectively, than those of the reported data. Overall, the proposed predictive model is a promising tool for predicting the qu of CTFSs, for instance, for ground improvement and cement-treated dredged soils.

Wave-Induced Liquefaction and Stability of Suction Bucket Foundation in Drum Centrifuge

Wave-Induced Liquefaction and Stability of Suction Bucket Foundation in Drum Centrifuge

Thermal Stabilization of Permafrost Using Thermal Coils Inside Foundation Piles

The article deals with the issue of thermal stabilization of soils to preserve the stability of pile foundations in permafrost conditions. The purpose of the work is to develop a technology for year-round freezing of soils by supplying coolant cooled by a refrigeration machine to thermal elements placed inside piles. In this work, the temperature regime of the system "pile foundation – soil" in the stationary formulation of the problem was simulated, and the influence of the depth of placement of thermal elements inside the piles on the soil temperature was investigated. The simulation was performed in the COMSOL software environment, taking into account the heat transfer due to thermal conduction and convection. In the presented model, a platform is fixed on piles, and a heat source is placed on the platform. It is found that an area of thawed soil has formed on the leeward side of the pile foundation. It is concluded that, under certain conditions, deep thermal elements for freezing or keeping the soil frozen should be placed at different depths. Thus, under given conditions, a greater depth of the thermal element placement in the pile, closest to the soil thawing zone, allows to reduce the surface temperature of the pile below ground level and, therefore, increase its bearing capacity. The authors also propose an original unit for soil thermostabilization based on the absorption cooling machine, which can operate at the expense of thermal energy generated by technological sources located on the platform. Doi: 10.28991/CEJ-2023-09-04-013 Full Text: PDF

A design analysis method and its application in the cover arch of cut-and-cover tunnels

It is very important to improve the design of supports because the cut and cover method of layered backfill after construction is the primary method used to construct shallow buried sections of mountain tunnels. The Dujuan Valley Tunnel in Fenghua City is the subject of this research. First, a geometric model of a shallow buried section of a mountain tunnel and its construction parameters were used to develop the simplified bearing capacity analysis model for the covered arch. Second, a simplified method to calculate the internal force of the cover arch supporting structure was established by using the method of structural mechanics. Thus, a method was established to determine the safe thickness of the cover arch and to analyze the bearing capacity and stability of the enlarged foundation of the arch foot. Third, the influence of the tunnel burial depth, cap arch sag height, central angle, radius and arch foot width on the bearing characteristics of the cover arch support structure was discussed, and the optimal design principle of excavation in shallow buried sections of mountain tunnels was obtained. Finally, the calculation and evaluation of the design in an example case were used to determine the rationality of the method to design and optimize shallow buried sections of mountain tunnels with the cut and cover method.

Silica fume stabilized loess: Mechanical properties, microstructural evolution and environmental analysis

The stabilization of loess is gaining increasing attention due to some of its physical properties which are highly prone to trigger some geological hazards. Common stabilizers (lime, cement and fly ash) release a significant proportion of greenhouse gases during their production, so it is becoming increasingly important to find an environmentally friendly or industrial waste material to stabilize loess. Silica fume is one such industrial waste material that can be used as a stabilizer in the stabilization of loess foundations. In this work, the unconfined compression strength of samples with different silica fume contents was measured, suggested that silica fume remarkably improved the strength for the samples. Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and energy-dispersive X-ray spectroscopy (EDXS) techniques were used to explore the microstructure and quantify the microstructural parameters through Image-Pro Plus (IPP) software to explain the variation in mechanical properties of samples with different silica fume content. The results indicated that the stabilization of the loess by silica fume consisted of both chemical and physical stabilization. Chemical stabilization was the reaction between silica fume and loess particles to produce C-S-H gels, while physical stabilization was the addition of silica fume which filled the pore volume and caused a variation in the shape and angle of the pores, thereby increasing the mechanical strength. The environmental impact of stabilizing 1 m3 of loess with a common stabilizer was studied by life cycle assessment (LCA) under similar unconfined compressed strength conditions, thus demonstrating the need to promote the use of silica fume in the loess foundation stabilization market.

Exploration of the slope effect on the uplift capacity of single straight and belled piles supporting transmission towers

Single piles are normally used to support the transmission tower in mountain areas. Uplift capacity of piles is a key factor in the engineering design to increase the stability of transmission tower foundation. This study numerically investigated the uplift capacity of single straight and belled piles in the sloping ground which consisted of a clay layer underlain by medium weathered sandstone. A non-linear 3D finite element model was proposed to describe the uplift behavior of single piles and was calibrated against a field test on single piles subjected to uplift loading. A parametric study was conducted to investigate the effect of the slope angle (θ) on the uplift behavior of single piles. The uplift capacity decreased as θ increased for either straight piles or belled piles. Moreover, the range of the equivalent plastic strain was greatest for single piles in the level ground. For piles in the sloping ground, the range of equivalent plastic strain was wider at the position of the downstream slope than that at the position of the upstream slope when the uplift load of single piles reached the maximum. As the expansion angle increased to 30° and 45°, the uplift capacity of belled piles (Ru) was increased by 100% and 180% with respect to that of straight piles, respectively. The increase percentage in Ru was independent of θ. A practical method was proposed to quantify the slope effect on Ru.

Analysis of the Failure Area of the Slope Using the Slip Line Method

Most geotechnical engineers focus on ground strength and stability. However, when determining stability by analyzing the exact strength of the ground, the failure surface is essential. Nevertheless, limited studies have been conducted on the methods to determine the exact failure surface of the ground. This study shows that the failure surface and plastic area can be analyzed using the slip line method based on the slip line and lower bound analysis. To improve existing studies limited to single ground, we analyzed the failure area of heterogeneous ground conditions. The results of the slip line method were compared and verified through FELM, a finite element analysis method to which a lower limit analysis was applied. As a result, the failure area and maximum internal stress according to the ground properties and the slope angle are presented. In addition, the points of the slip line method and the finite element limit analysis are summarized. Finally, we propose limitations and solutions when applying the slip line method to the slope.

Experimental and numerical research on the wet-towing of wide-shallow bucket jacket foundation for offshore substation

Offshore wind power is a kind of clean and renewable energy. In recent years, offshore wind power has been exploited more and more widely. With the hub of power collection of offshore wind farm, the offshore substation becomes an important facility for offshore wind power transmission and transformation. In this paper, the current situation of the foundation and installation mode of offshore wind farm substation are introduced, with emphasis on an integral wet-towing method based on a wide-shallow bucket jacket foundation (WSBJF). Firstly, based on the advantages of the integral installation mode of offshore wind power and the composite bucket foundation, the WSBJF of offshore substation is proposed. Secondly, the wet-towing method and the corresponding construction processes of WSBJF are elaborated, and the feasibility of the wet-towing method is verified by the indoor model experiments and numerical simulation analysis. Finally, with the help of the model experiments and numerical simulation, the effects of draft depth, wave height and wave period on foundation stability and dynamic response are investigated. The results show that it is feasible to carry out long distance wet-towing of the foundation under the condition of level 5 wind and waves. WSBJF has a certain self-floating ability, which can meet the wet-towing stability requirements without upper platform. Reducing draft depth and increasing wave height will reduce the stability of WSBJF during wet-towing. Under the premise of a certain draft depth of the foundation, when the wave period is close to the natural period of the WSBJF, the WSBJF will be rocked greatly. For example, the pitch angle of the WSBJF at 14 s wave period is 56 times that at 6 s wave period.

Automating the Process for Estimating Tunneling Induced Ground Stability and Settlement

An automatic process for estimating ground stability and settlement of circular tunnels is developed for practitioners in this paper using finite difference method FLAC code. The numerical model aims to simulate the movement and relaxation of the soil around the shield and lining annulus that occurs due to the overcutting and grouting of the tunnel void by a tunnel boring machine. To achieve this, the model uses a pressure relaxation technique that progressively reduces the tunnel support pressure from the initial at rest condition until a point of failure is detected. At this stage, the stability number is calculated, and settlement data are exported for analysis. This is conducted for a range of geometry and soil ratios which cover most practical cases for cohesive soils. These stability numbers are then compared to rigorous upper and lower bound solutions. Using the settlement data, a trough width parameter ix is also determined for each case using regression of the commonly used Gaussian equation. The results of this study are quite positive, with the stability results from this study remaining within 5% of the upper and lower bound solutions; settlement results also compare well with previous experimental and observational results. The proposed automatic process can be used effectively and efficiently in most practical design projects.

Hydromechanical behaviour of columnar jointed rock masses under true triaxial conditions: An experimental and theoretical investigation

Understanding the hydromechanical behaviour of columnar jointed rock masses (CJRMs) is crucial for reservoir evaluation in oil and gas engineering and dam foundation stability control in water conservancy projects. According to the natural structural characteristics of the CJRM, artificial samples with diverse dip angles (β = 0°–90°) were poured through the self-designed mould, and several true triaxial seepage tests had been done. Based on the test results, the anisotropy of the permeability and the stress sensitivity of the CJRM at different loading stages were discussed, and a two-stage permeability model was established according to the change in volumetric strain. Under the true triaxial conditions, the seepage characteristics of the CJRM have strong stress sensitivity, showing obvious U-shaped seepage variation characteristics. The existence of the dip angle greatly affects the anisotropic seepage characteristics as well as the failure mode of the CJRM, when the dip angle is between 45° and 75°, the failure mode is mainly structural failure, and the volume expansion is the most intense. Finally, the two-stage permeability model that proposed in this study is fitted with three groups of different experimental data, and the fitting results show the model can effectively reflect the variation law of the permeability characteristics under full stress conditions, indicating that the volume strain as a characterization parameter for predicting the change in permeability characteristics has strong applicability. The research results can make a more effective understanding of the permeability variation characteristics of jointed rock masses.

The research about application of quasi-zero stiffness vibration isolation technology in a large vehicle-mounted optic-electronic equipment

The large vehicle-borne optic-electronic tracking equipment has the characteristics of heavy inertia, complex road condition and wide vibration spectrum. In order to solve the problem of passive broadband vibration isolation for vehicle-mounted moving platform optic-electronic equipment, a combined quasi-zero stiffness vibration isolation scheme is proposed. The vibration of the engine, generator, water cooler and the remaining vibration amplitude, frequency and Yaw of the road after passing the self-vibration isolation system of the vehicle are collected and confirmed by means of calculation simulation and field test. At the same time, the effective load of photoelectric equipment is analyzed by frequency sweeping test, and the corresponding multi-mode frequency points are obtained. According to the characteristics of the special equipment, a quasi-zero-stiffness vibration isolation system is designed to suppress the wide-frequency and high-amplitude vibration and Yaw caused by vehicle-borne vibration source, ground vibration source and resonance point of the equipment, the foundation stability of load equipment under dynamic condition is realized, which provides a condition for solving the problem of high precision and stability tracking which is greatly influenced by vibration. The vibration isolation system can realize the vibration isolation efficiency of 90% in the range of 20 Hz to 2000 Hz under the condition of 60 Km/h three-class highway with 1.5 t photoelectric load, and restrain the deflection caused by unbalance torque and vibration source offset effectively. It can be concluded that the quasi-zero stiffness vibration reduction and isolation combination design can effectively suppress the vibration of the large-scale vehicle-mounted optic-electronic equipment under the condition of moving platform.