International Journal of Civil Engineering
Volume:17 Issue: 6, June 2019

Ground movements due to deep excavation may cause damage or loss of functionality to nearby building, especially in urban areas: embedded diaphragm walls between the new and the existing buildings can be effective in reducing these movements. The paper reports the results of an experimental and numerical study carried on a full-scale anchored piles diaphragm used to supporting deep excavation in urban area devoted to the new Library of the University of Enna “Kore”, Enna (Italy). Two piles, located in the central part of the diaphragm wall, have been instrumented with conventional inclinometer cases and embedded piezoelectric accelerometers. The experimental measurements recorded during the construction and in operation are reported and discussed in detail. Plane strain finite element analyses using the code PLAXIS 2D are presented in which the diaphragm was modelled to evaluate the geotechnical system behavior. It has been observed that this model allows for a satisfactory simulation of the displacement of the wall during the construction phases under a static loading scenario. The results in terms of horizontal displacements obtained by numerical modelling are in good agreement with those derived by measurements. Furthermore, on the basis of measured data, an empirical method has been used to evaluate the surface settlements, whose values guarantee a good safety threshold to the nearby building.

The effect of slope-stabilizing stone columns on the bearing capacity of a rigid strip footing placed on a sand slope has experimentally and numerically investigated in this paper. A broad series of conditions has been tested by varying parameters such as the rigidity of stone columns and their spacing in a row. Different types of stone columns were studied including ordinary stone columns, encased stone columns, and concrete piles. Soil displacement fields were obtained via particle image velocimetry method. The results were analyzed to find qualitative and quantitative relationships among bearing capacity and various parameters. A series of finite-element analyses was additionally carried out on a prototype slope and the findings were compared with the results from the laboratory model tests. They were also used to complement the results of the model tests. The agreement between observed and computed results is found to be reasonably good in terms of load–settlement behavior and optimum parameters. Findings of the study showed that increasing rigidity and decreasing the stone columns spaces result in increasing bearing capacity of footing. This enhancement in bearing capacity is attributed to arching effect of soil between stone columns. The rigidity and spacing of stone columns had a significant effect on soil arching. Moreover, the load–settlement behavior of rigid footing is improved.

Study on shear strength and compressibility characteristics of soils considering anisotropy phenomenon is essential to the accurate design of structure foundations and stability analysis of earth structures. In this research, a series of triaxial and oedometer tests were used to study the mechanical behavior of a fine-grained cohesive soil considering the effect of inherent anisotropy on the behavior. For this purpose, a special soil sampler was made and different directions were selected to collect the samples from the site. All triaxial samples were isotropically consolidated under the effective stresses of 200, 300 and 500 kPa, and loaded at the rate of 0.05 mm/min. The results showed that the shear strength and compressibility of the soil intensively depend on the sampling direction. With an increase in the anisotropic angle, the shear strength values decreased and the settlement values increased. However, at the anisotropic angle of 72°, the shear strength and settlement have minimum and maximum values, respectively. In addition, a review of failure surface illustrates that as the angle between the failure surface and the bedding direction decreases, the failure surface tends to be closer to soil stratification and it causes an increment in pore water pressure and reduction in shear strength. In general, samples cored perpendicular to the bedding direction showed dilative behavior, whereas the other ones exhibited contractive behavior.

The maximum dynamic shear modulus (Gmax) of soils is a fundamental parameter used in the evaluation of soil dynamic behavior and seismic design in geotechnical engineering. In this study, seismic piezocone (SCPTU) and resonant column (RCT) test methods were adopted for measuring soil shear wave velocity (Vs) in Jiangsu Province of China. Then, the relationship between the Gmax and SCPTU test parameters was established based on the test data of shear wave velocity. The results show that using the correlation between the cone resistance (qt) and void ratio (e) or pore pressure parameter (Bq) to evaluate Gmax was better than using the single-cone tip resistance parameters. The Gmax of the soft soil can be determined more accurately using the cone tip resistance and pore pressure parameters measured by the SCPTU test method, and corrected based on the laboratory test data. The evaluation of Gmax based on the RCT test results was not satisfactory due to the soil disturbance induced during sampling and testing processes.

Presence of reinforcement elements such as geogrid in the cushion layer of the non-connected pile raft foundation changes the load transition mechanism and the portion of piles and raft from the total load. In this paper, experimental studies have been conducted on a non-connected pile raft foundation located in a sandy soil. The effect of parameters such as piles spacing, the thickness of cushion, position, length and number of geogrid layers on the behavior of load settlement, the portion of piles and raft from the total load, and distribution of axial and frictional stress along the pile and position of neutral axis were studied. The results showed that in unreinforced cases, with an optimum cushion thickness and piles spacing, the lowest settlement is observed. The use of geogrid in the cushion layer increases the bearing capacity and the portion of the piles from the total load and led to a move up in the neutral axis to the top of the piles. The optimum position and length of the first and second geogrid layers have also been studied.

Seismic piezocone penetration tests, resistivity piezocone penetration tests, and standard penetration tests (SPT) were conducted to quantitatively assess the effects of soil improvement by vibro-compaction. The differences of piezocone penetration test (CPTU) basis readings, improvement index for densification, electrical resistivity of soils, and state parameters before and after ground treatment were analyzed, and the effect of the increase in stiffness on the site response was also analyzed for the effect of densification. A combination of shear wave velocity, Vs, and cone tip resistance, qc, was used for the interpretation of the changes of coefficient of earth pressure at rest, K0, and mean grain size, D50, before and after compaction. The dissipation process of excess pore pressures during vibro-compaction has been presented to show the effect of drainage. In addition, liquefaction potential was also estimated by CPTU and SPT for its effect of reinforcement. The results showed that the liquefied soil was densified and the use of a combination of in-situ tests could be used for ground improvement needed to mitigate liquefaction.

The interference of two nearby footings has been challenging due to the lack of suitable construction sites. Therefore, engineers are often forced to place footings at close spacing, which results changing of the ultimate bearing capacity, the settlement, and the tilt based on the considered spacing. In this study, two series of 1 g model test were conducted on two interfering parallel strip footings rested on the Babolsar saturated sand with different safety factors considered for the previously constructed footing (named as the old footing). The footings are loaded unequally and non-simultaneously to simulate mechanism of the new and the old footing with different surcharge and construction orders. The results are presented in the form of non-dimensional interference factors for ultimate bearing capacity and settlement of interfering footings versus isolated footings. It is demonstrated that the interference effect on the performance of isolated footings is considerable. Moreover, by decreasing the S/B ratio (i.e., spacing divided by footing width) from 1 to 0, the settlement ratio increases more than five times. Furthermore, in both series of tests, more than 300% increase in the tilting degree of the old footing was resulted due to the interference with the new footing in the ratio of S/B = 0 compared with S/B = 1. It demonstrates the perilous effect of the old footing tilting caused by the new footing adjacency. Moreover, applying different safety factors for the old footing has no dramatic effect on the tilting of the old footing enforced by the adjacent new footing.

After excavation beneath existing basement of a pile-supported building, prediction of the pile response is an interesting topic in geotechnical engineering. This paper presents a new load transfer function to capture the relationship between unit skin friction and shaft displacement. As to the load transfer function of an individual pile in pile groups before and after excavation, load transfer functions of skin friction and end resistance are proposed considering interactive effects among piles. To get a quick estimation on the pile response before and after excavation, a new highly effective iterative computer program is proposed using the proposed load transfer functions. Comparisons of the measured results, the present computed results and the calculated values derived from other approaches are made to check the reliability of the proposed method. Furthermore, a parameter study is carried out to evaluate the ultimate value of skin friction and end resistance of the pile subjected to stress relief due to excavation, and the influence of the parameters related to the proposed load transfer models on the pile response is also evaluated.

A series of laboratory large-scale model tests were conducted on piled raft founded on sand with different compaction levels. The numbers of piles are 1, 4, 5 and 9. All the piles are 40 cm in length and the slenderness ratio is 20. In these tests, the variation of load improvement ratio (LIR), load-sharing ratio (αp) and settlement ratio (SR) are reported for different relative densities and number of piles. Moreover, the variation of ultimate bearing capacity of piled raft system was investigated for different conditions. Results showed that LIR ratio will be more noticeable in loose state in comparison to dense sand, and also increasing the number of settlement reducing piles proved to decrease the SR values or increasing the SIF values in other words. In the end, a sensitivity analysis was performed to investigate the influence of each parameter in affecting the performance of the piled raft system. Based on the sensitivity analyses, relative density of soil was proven to be the most effective parameter in comparison to the number of piles. Finite element analyses have also been performed using the ABAQUS software. The numerical results from the FEM were first validated with the experimental results and then parametric study was carried out to investigate the effect of load eccentricities. It was shown that the ultimate bearing capacity of the piled raft foundation decreases significantly with an increase in the load eccentricity.

The present study investigates the hysteresis response, stiffness degradation/cyclic softening and energy dissipation features of Ahmedabad cohesive soil. Saturated specimens of Ahmedabad cohesive soil were reconstituted using slurry consolidation technique at different void ratios to perform the following series of tests, strain-controlled cyclic triaxial tests, shear strength, and compressibility tests. Load repetition exhibited significant degradation in shear modulus of slurry consolidated cohesive soil specimens under cyclic loading conditions. A maximum stiffness degradation of 78% was observed for the specimen possessing minimum initial void ratio. Hysteresis response of Ahmedabad soil revealed alteration in the rotation angle of hysteresis loops and their sizes with varying initial void ratios of the Ahmedabad cohesive soil. A substantial influence of initial void ratio on the energy dissipation behavior of cohesive soil was depicted in the present study. The cumulative energy dissipation of the specimen prepared with lower initial void ratio was obtained to be 7.1 times higher than the specimen possessing maximum initial void ratio.

The load response and carrying mechanism of piles in a non-connected piled raft foundation is a complex phenomenon due to complex soil–structure interactions such as interactions among piles, subsoil, cushion, and raft. The scope of this research includes four main components: (1) using 3D finite element modeling and verifying different models with centrifuge tests; (2) investigating the parameters affecting the axial stiffness of a non-connected piled raft; (3) investigating the influence of different parameters on the foundation settlement; and (4) devoting special attention to the mechanism of carrying and sharing loads as well as the load–settlement behavior of non-connected piled raft foundations, in comparison with connected piled raft foundations. Results of this research showed that in order to achieve optimal design, geotechnical designers should consider three major factors, including axial stiffness of non-connected piled raft, settlement, and stress along the pile length.

To better understand the mechanism of development of lateral resistance of single drilled piles installed in improved soil profile. Side-by-side static load tests were performed on the piles installed in virgin soil profile and improved soil profile with the soil ahead of the pile cement-improved. Parametric three-dimensional finite element analyses were performed to study the effect of grouting radius. More soils at the side of piles make a critical contribution to resisting lateral loads due to the influence of improved soil ahead of the pile. A new hyperbolic p–y function that modifies the initial subgrade modulus and the ultimate lateral soil resistance is proposed based on the finite element analyses to account for the effect of the cement improvement. The proposed p–y method is capable of predicting laterally loaded pile response in cement-improved soil profiles as measured in the static load tests. The accuracy of the proposed p–y model is appropriate as shown by comparing measured and calculated the lateral behaviour of the single pile.

This study presents the formulation of a finite-element numerical method for the analysis of shear wave dispersion out of plane SH. Also, it evaluates the seismic behavior of alluvial valleys located in a semi-infinite rigid space. This formulation is implemented in computer codes in time domain. To examine the accuracy of the program, various examples are solved and some numerical considerations in the dynamic analysis of the topographic feature are investigated by parametric studies. The results indicate that the appropriate time step in the finite-element method (FEM) is 45/1000 of the predominant period of the incident wave. The appropriate length of the element should be selected for placing at least eight nodes on the smallest wavelength. Increasing Gaussian points in integrating mass matrices in comparison with stiffness matrices is not effective in the accuracy of results. It was found that the choice of δ > 0.5 in Newmark’s integration method reduced the amplitude, but the change in the α value did not affect the results. The effect of a feature on the ground response is only noticeable if the wavelengths are comparable with the dimensions of the feature.

In this study, the unconfined compressive and cyclic behaviors of saturated mucky silty clay from the reclamation area of Dalian, which has two different clay contents, are investigated using the static and dynamic triaxial test systems. The influence of clay content on the residual strain and residual pore water pressure of undisturbed and reconstituted specimens are discussed. A scanning electron microscope (SEM) is used to observe the microstructures of the specimens. The unconfined compressive test results of the specimen with low clay content exhibits “collapse” characteristics. However, the corresponding specimen with high clay content exhibits a “sustained hardening” trend. The dynamic test results indicate that the residual pore water pressure, residual strain, and difference in the residual strain between the undisturbed and reconstituted specimens increase as the load increases. The ratio of the reconstituted residual strain to the undisturbed residual strain increases as the load increases, and this ratio is larger than the sensitivity of the soil. The residual strain of the specimen with high clay content exceeds the corresponding value of the specimen with low clay content. The stiffness degradation of the high clay content specimen is more obvious than that of the low clay content specimen. A power function-based residual strain model that contains the cyclic stress ratio (CSR) and number of cycles (N) is proposed. This model can be used to describe the residual strain with a CSR less than the critical CSR.

Construction of a dam cut-off wall is one of the most challenging tasks in dam engineering given the deep excavations involved and the complex interactions between stiff cut-off walls and soft surrounding soils. Here, we present innovative solutions for the development of the Karkheh dam’s complementary cut-off wall in southwest Iran which is among the largest structures of this type worldwide with a maximum depth of 115 m. Due to excessive water seepage and high hydraulic gradient following the reservoir impoundment, additional measures were considered among which was the extension of the existing cut-off wall. The main goal was to decrease the hydraulic gradient of the seepage through the dam foundation. The construction of this new wall, which is called as the complementary wall here, was associated with a number of technical challenges among which were: the connection between the new and old walls; trenching and placing of plastic concrete wall through different dam body zones; and slurry loss during trenching through the dam body zones. The complementary wall was constructed successfully producing invaluable engineering experiences including: design of a U-shaped panel as the connecting panel; design of a new method for grouting through uniformly distributed filter/drain materials; and adding cement-based grouts to the cut-off wall panels to prevent slurry loss. The complementary wall helped to decrease both total seepage and the hydraulic gradient; for instance, in the right abutment, total seepage was cut for 25% and the hydraulic gradient was reduced from 0.2 to 0.095.

One of the most important statistical parameters in modeling the spatial correlation of soil properties in a random field is the scale of fluctuation (SoF), which is strongly affected by the sampling interval. In this study, the effect of the sampling interval on the SoF in the vertical direction was examined using cone tip resistance (qc) profiles of 70 CPT datasets. The qc data intervals in the vertical directions were 2.5 cm, 5 cm, 10 cm, 20 cm, 40 cm, 80 cm, 160 cm and 320 cm. The direct integration of sample autocorrelation function method with quadratic trend removal was adopted to determine the SoF. Variation of the calculated SoF versus the extended sampling intervals demonstrates that the SoF increases with the increase in the sampling intervals. Results show that the determined SoF values based on the geotechnical data sampling intervals up to 40 cm are presumably more reliable. Limiting the sampling interval will contribute to the preservation of important correlation information of geotechnical site investigation data.

New installation methods and techniques using single-point settlement gauges to monitor the compression deformations of pile shafts and soil layers below the pile bottom were developed. A field study was conducted at a test site of the Beijing–Shanghai high-speed railway, and a 3D finite-element analysis was performed to analyze the deformation behavior of the pile foundation. The measured compression deformations of the pile shafts from the single-point settlement gauges agreed well with the values obtained from the strain gauges, which validated the effectiveness and feasibility of the developed methods and techniques. During the construction of the high-speed railway, the pile top settlement–time curve presented a ‘ladder’ shape and then increased with time before gradually stabilizing. The compression deformations of the subsoil layers within 20–30 m below the pile bottom were not significantly different, and the average unit compression deformation under 20 m below the pile bottom remained approximately constant after construction. The axial force and tip resistance of the pile shaft increased during the consolidation of the soils surrounding the pile shaft and might result in an increase of the compressions of the pile shaft and subsoil layers. The thicknesses of compressible layers (hc) of the tested pile foundations were determined using a deformation ratio method and were approximately 15.0 m. These results demonstrate that the developed methods and techniques are useful for studying the compression deformations of subsoils below the pile bottom (especially for super-long piles).

This study was aimed to determine the influence of the aeration on some of the leachate properties and geotechnical aspects of the fresh municipal solid waste (MSW) in laboratory obtained from Barmshoor landfill, Iran. Two different bioreactors were filled with the same MSW in the laboratory and cured under anaerobic and aerobic conditions for 200 days. Temperature variation, the rate of leachate generation and its properties (pH, COD, BOD and organic content) as well as the shear strength parameters and settlement of the MSW for each bioreactor were measured in curing of the bioreactors. Aeration causes the temperature of the aerated sample to increase considerably. The temperature difference between the two bioreactors becomes about 7 °C after 200 days. For the aerated bioreactor, leachate volume decreased, then increased and finally, it reduced to the end of the experiment. The aerated sample produces less leachate compared to the blank sample. Aeration of MSW has significantly reduced COD of the generated leachate after 120 days. The COD/BOD ratio is remaining constant for the aerated sample (less than 1.6) during the experiment. However, it increases in the case of the blank sample after 60th day and reaches to more than 5 at the end of the experiment. Therefore, waste aeration can eliminate some complicated organic materials due to the presence of oxygen in the injected air. Comparing the results of the direct shear test of both bioreactors indicates that the aeration increases the shear strength at the end of the procedure.

The behaviour of granular soil is mainly dependent upon the nature and arrangement of particles, which in turn affect fabric anisotropy. It has been known for many years that depositional method plays an important role in the results of laboratory testing of granular soils. Despite extensive studies on the dynamic properties of granular soil, previous research has lacked a quantitative study of the effects of depositional methods on the dynamic properties of the granular soil. The primary objective of the current study was to evaluate the effect of fabric anisotropy on the dynamic properties of granular soil for practical applications. The influence of depositional method, mean effective consolidation stress, shear strain amplitude and relative density on the maximum shear modulus (Gmax), shear modulus curve (G-γ), normalized modulus curve (G/Gmax-γ) and damping curve (D-γ) of pure sand, pure gravel and sand-gravel mixtures is investigated. The results of the tests indicate that depositional method has a significant effect on Gmax that this effect was more pronounced for the pure sand specimens than for the pure gravel or sand-gravel mixture specimens. However, the depositional method had no significant effect on the shear modulus at large shear strain amplitudes. The effects of depositional method on the G/Gmax-γ and D-γ curves are dependent on effective confining pressure and relative density.

Shear strength of a sandstone–mudstone particle mixture, filled along the bank of a large reservoir and subjected to wet–dry cycle induced by the rise–lower cycle of water level, may be affected by the wet–dry cycle. To investigate the effects, two-type triaxial tests, without and with the wet–dry cycle, were carried out. The experimental data indicate that the shear strength, denoted by peak deviator stress (σ1 − σ3)f, angle of shearing resistance φ, nonlinear shear strength indicators φ0 and φd, or linear shear strength indicators φ* and c, is reduced by the wet–dry cycle. With the increment of cycle from 1 to 20, the decrement of shear strength, denoted by the parameters mentioned above, is increasing in a logarithmic relationship. Furthermore, the effect is also related to the confining pressure and stress level selected in the tests. Based on analyzing experimental data, several logarithmic functions, used to predict the shear strength of the mixture after the wet–dry cycle, were suggested. Due to the effect of the wet–dry cycle, stability of a slope, filled in waterfront conditions using the mixture, is reduced.