The construction of combined pile-raft foundations is considered as the main option in designing foundations in high-rise buildings, especially in soils close to the ground surface which do not have sufficient bearing capacity to withstand building loads. This paper deals with the geotechnical report of the Northern Fereshteh area of Tabriz, Iran, and compares the characteristics of the single pile foundation with the two foundations of pile group and geogrid. Besides, we investigate the effects of five principal parameters including pile diameter and length, the number of geogrid layers, the depth of groundwater level, and pore water pressure on vertical consolidation settlement and pore water pressure changes over a year. This study assessed the mechanism of the failure of the soil under the foundation using numerical analysis as well. Numerical analysis was performed using the two-dimensional finite element PLAXIS software. The results of fifty-four models indicate that the diameter of the pile tip, either as a pile group or as a single pile, did not have a significant effect on the reduction of the consolidation settlement in the soil in the Northern Fereshteh Street region. The optimum length for the pile in the Northern Fereshteh area is 12 meters, which is economically feasible. In addition, the construction of four-layered ten-meter-long geogrids at intervals of 1 meter beneath the deep foundation had a significant preventive impact on the consolidation settlement in clayey soils.

The dynamic response of crossing tunnels under heavy-haul train loads is still not fully understood. In this study, based on the case of a high-speed tunnel underneath an existing heavy-haul railway tunnel, a model experiment was performed to research the dynamic response characteristics of crossing tunnels. It is found that the under-crossing changes the dynamic response of the existing tunnel and surrounding rock. The acceleration response of the existing tunnel enhances, and the dynamic stress of rock mass between crossing tunnels decreases after the excavation. Both tunneling and the excitation of heavy-haul train loads stretch the tunnel base, and the maximum tensile strain is 18.35 µε in this model test. Then, the measured results were validated by numerical simulation. Also, a parametric study was performed to discuss the influence of the relative position between crossing tunnels and the advanced support on the dynamic behavior of the existing tunnel, where an amplifying coefficient of tunnel vibration was introduced to describe the change in acceleration due to tunneling. These results reveal the dynamic amplifying phenomenon of the existing tunnel during the new tunnel construction, which can be referred in the dynamic design of crossing tunnels.

Rock damage is the main cause of accidents in underground engineering. It is difficult to predict rock damage accurately by using only one parameter. In this study, a rock failure prediction model was established by using stress, energy, and damage. The prediction level was divided into three levels according to the ratio of the damage threshold stress to the peak stress. A classification predicting model was established, including the stress, energy, damage and AE impact rate using Bayesian method. Results show that the model is good practicability and effectiveness in predicting the degree of rock failure. On the basis of this, a multi-parameter classification predicting deterioration model of rock failure was established. The results provide a new idea for classifying and predicting rockburst.

In the design of geotechnical structures, engineers choose either peak or critical state friction angles. Unfortunately, this selection is based on engineer's preference for economy or safety and lacks the assessment of the expected level of deformation. To fill this gap in the design process, this study proposes a strain based empirical method. Proposed method is founded on the experimentally supported assumption that higher dilatancy angles result in more brittle soil response. Using numerous triaxial test data on ten different soils, an empirical design chart is developed that allows the estimation of shear strain at failure based on soil's peak dilatancy angle and mean grain diameter. Developed empirical chart is verified by conducting a small scale retaining wall physical model test. Finally, a design methodology is proposed that makes the selection of design friction angle in structured way possible based on the serviceability limits of the proposed structure.

Evaluation of earthquake impacts in settlements with a high risk of earthquake occurrence is important for the determination of site-specific dynamic soil parameters and earthquake-resistant structural planning. In this study, dynamic soil properties of Karliova (Bingol) city center, located near to the intersection point of the North Anatolian Fault Zone and the East Anatolian Fault Zone and therefore having a high earthquake risk, were investigated by one-dimensional equivalent linear site response analysis. From ground response analyses, peak ground acceleration, predominant site period, 0.2-sec and 1-sec spectral accelerations and soil amplification maps of the study area were obtained for both near-field and far-field earthquake effects. The average acceleration spectrum obtained from analysis, for a near-field earthquake scenario, was found to exceed the design spectra of the Turkish Earthquake Code and Eurocode 8. Yet, the average acceleration spectrum was found to remain below the respective design spectra of the two codes for the far-field earthquake scenario. According to both near- and far-field earthquake scenarios in the study area, the low-rise buildings with low modal vibration durations are expected to be exposed to high spectral acceleration values and high-rise buildings with high modal vibration durations will be exposed to lower spectral accelerations. While high amplification ratios are observed in the north of the study area for the near-distance earthquake scenario, high amplification ratios are observed in the south of the study area for the long-distance earthquake scenario.

A novel approach for predicting lateral displacement caused by pile installation in anisotropic clay is presented, on the basis of the cylindrical and spherical cavities expansion theory. The K₀-based modified Cam-clay (K₀-MCC) model is adopted for the K₀-consolidated clay and the process of pile installation is taken as the cavity expansion problem in undrained condition. The radial displacement of plastic region is obtained by combining the cavity wall boundary and the elastic-plastic (EP) boundary conditions. The predicted equations of lateral displacement during single pile and multi-pile installation are proposed, and the hydraulic fracture problem in the vicinity of the pile tip is investigated. The comparison between the lateral displacement obtained from the presented approach and the measured data from Chai et al. (2005) is carried out and shows a good agreement. It is suggested that the presented approach is a useful tool for the design of soft subsoil improvement resulting from the pile installation.

In recent years, the stability, safety and comfort of trains has received increased attention. The mechanical characteristics and differential settlement of the foundation are the main problems studied in high-speed railway research. The mechanical characteristics and differential settlement of the foundation are greatly affected by the ground treatment. Additionally, the effects of train load and earthquakes have a great impact. The dynamic action of the train will increase the vibration acceleration of the foundation and increase the cumulative deformation, and the earthquake action will affect the stability of the substructure. Earthquakes have an important practical significance for the dynamic analysis of the railway operation stage; therefore, considering the impact of earthquakes on the railway substructure stability has engineering significance. In this paper, finite element model of the CFG (Cement Fly-ash Gravel) pile + cement-soil compacted pile about composite foundation is established, and manual numerical incentive method is selected as the simulation principle. The mechanical characteristics and differential settlement of CFG pile + cement-soil compacted pile about composite foundation under train load are studied. The results show: under the train load, the neutral point of the side friction about CFG pile is located at nearly 7/8 of the pile length; the vertical dynamic stress-time history curves of the cement-soil compacted pile, CFG pile and soil between piles are all regular serrated shape, the vertical dynamic stress of CFG pile changes greatly, but the vertical dynamic stress of cement-soil compacted pile and soil between piles does not change much; the vertical displacement of CFG pile, cement-soil compacted pile and soil between piles change very little.

The enzyme-induced carbonate precipitation (EICP) method has been investigated to improve the hydro-mechanical properties of natural soil deposits. This study was conducted to explore the stiffness evolution during various stress scenarios. First, the optimal concentration of urea, CaCl₂, and urease for the maximum efficiency of calcite precipitation was identified. The results show that the optimal recipe is 0.5 g/L and 0.9 g/L of urease for 0.5 M CaCl₂ and 1 M CaCl₂ solutions with a urea-CaCl₂ molar ratio of 1.5. The shear stiffness of EICP-treated sands remains constant up to debonding stresses, and further loading induces the reduction of S-wave velocity. It was also found that the debonding stress at which stiffness loss occurs depends on the void ratio, not on cementation solution. Repeated loading-unloading deteriorates the bonding quality, thereby reducing the debonding stress. Scanning electron microscopy and X-ray images reveal that higher concentrations of CaCl₂ solution facilitate heterogeneous nucleation to form larger CaCO₃ nodules and 11-12 % of CaCO₃ forms at the interparticle contact as the main contributor to the evolution of shear stiffness.