Predicting the settlement of geogrid-reinforced soil foundations in railway track using cuttlefish algorithm

Shallow foundations are one of the most common methods for transmitting loads of structures to the underlying ground. Design standards are often based on the bearing capacity of shallow foundations in saturated soils or dry soils. However, many shallow foundations are located within unsaturated soil above the groundwater table. Although experimental studies show that the bearing capacity is significantly increased by the presence of suction in unsaturated soils, the foundation settlement caused by infiltration, e.g., due to rainfall and pipe leaking, may develop further problems for structures, such as wall cracks, sticking windows and doors and the presence of water in basements. This kind of damage is happening more often now, with more extreme weather conditions as a result of climate change. A finite element model has been developed in this paper to analyse shallow foundation behaviour under infiltration conditions. An advanced unsaturated soil model has been implemented in the finite element code that considers the soil-water retention with hysteresis and deformation dependency. Numerical analysis results indicate that the foundation settlement is significantly influenced by the hydraulic history (seasonal changes with drying-wetting cycles), and hydraulic hysteresis should be included in the numerical analysis of the mechanical response of shallow foundations in unsaturated soils.KeywordsShallow foundationFinite element methodUnsaturated soilsFooting analysis

Face stability and ground settlement in shield tunneling : Romo, M P; Diaz, C M Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V1, P357–360. Publ Rotterdam: A. A. Balkema, 1981

The fine numerical simulation is used to study the ground settlement of complex stratum owing to shield construction by ANSYS program. It is shown that the closer the distance between soil layer and the axis of tunnel is, the smaller the disturbance of construction is, the obvious the ground surface settlement is. The value of the maximum settlement at the center of the surface is 7.4mm. The maximum settlement of vault is 14mm. The ground subsidence in cross section distribution is shaped of normal distribution. The closer the distance between soil layer and ground surface is, the smaller the vertical displacement is, the bigger the width of settlement trough of soil layers is. The width of settlement trough is 25m. The volume loss rate of shield tunnel is about 0.32%. The width coefficient of ground settlement trough is 0.56. The tendency of ground settlement decrease to become gentle with the advance of shield construction. The ground settlement keeps constant after tunnel face advancing to 30m.

Convergence of Galerkin truncation for dynamic response of finite beams on nonlinear foundations under a moving load

A case study of sewerage pipeline installation utilizing pipe jacking and MTBM in Ipoh, Perak, Malaysia was conducted to analyse the ground response by quantifying the soil volume loss and ground surface settlement. The sewerage pipeline installation involves tunnelling and jacking beneath the KTMB railway track for 191m from jacking to receiving pit.The excessive horizontal and vertical deviation of MTBM when excavating through very loose sand and soft clay leads to an uncontrolled overcut and affecting the magnitude of the ground surface settlement where 100mm and 130mm for horizontal and vertical deviation respectively produce 49mm of ground surface settlement. The maximum settlement for the railway track was 12mm over 30m chords length (0.0004) after two months of project completion still within the allowable limit set by KTMB (11mm over 10m chords for intervention (0.001). The volume loss calculated from this project ranging from 0.80% to 12.68% contributes by the lowest and the highest ground surface settlement which is - 3mm and - 51 mm, respectively which varied from the 8mm estimated ground surface settlement by assuming 2% of volume loss. It was found that the trough width parameter K = 0.5 matches the settlement trough of collected field data. In conclusion, soil volume loss and ground surface settlement was affected by the MTBM deviation.

Calculation Method of Underground Passage Excavation on Interactive Effects among Pipe-Roof, Steel Bracing and Foundation Soil

Sand-rubber mixtures have the advantages of light weight, high strength, and low price. In this study, three-dimensional finite element simulation was carried out in GTS MIDAS based on the elastoplastic constitutive model to investigate the response of bridge abutments to sand-rubber mixtures backfills under static load condition. Four different backfill materials were used and compared in the modeling. The settlement of abutment foundation, displacements of bridge abutment and foundation pile, and bending moment of the piles were analyzed. The results show that the sand-rubber mixtures backfill can significantly decrease the settlement of foundation, and the displacements of bridge abutment and foundation pile as compared to the backfill soil. Such decrease is more prominent as the rubber content increases. The use of sand-rubber mixtures replacing the soft soil layer or as a backfill material not can only reduce the upper load acting on foundation soils and improve the stability and static performance of bridge abutment, but also solve the problem of waste rubber recycling and potential environmental pollution to meet the increasing demand of road construction materials for the rapid development of highway engineering, resulting in huge economic and social benefits with a wide range of engineering applications.

8 - CPT and CPTu for foundation settlement and load–displacement (P-Δ) estimation

[Extract] Soil mechanics and foundation engineering go hand in hand. While there were so many new frontiers in different areas (e.g. geosynthetics, environmental geotechnics, instrumentation) related to geotechnical engineering, there have been significant advancements in the core area of foundation engineering during the past few decades. The objective of this special issue is to bring together some recent developments in foundation engineering in all fronts such as analytical studies, model tests in laboratories, and numerical modelling. There are ten papers in this special issue, covering a wide range of topics related to bearing capacity and settlements of foundations. While having the emphasis on shallow foundations, we have also included an interesting paper on piles that deals with the prediction of pile group capacity.

In the transition zone of railway tracks, track irregularities occur frequently due to differential settlement, which arises from the difference between the vertical supporting stiffness of the abutment and the backfill. This is disadvantageous because it increases the maintenance requirements and deteriorates the ride quality. To address this challenge, this study proposes a strategy involving the application of cement-treated gravel reinforced with geogrids and rigid facing walls. The reinforced subgrade for railways (RSR), which can reduce residual settlement through the initial construction of the backfill reinforced with geogrids and the subsequent development of the rigid facing wall, was constructed at the transition zone with cement-treated gravel as the backfill material. The long-term behaviors during and after construction on the RSR for a period of 16 months were evaluated by analyzing the surface and ground settlements, horizontal earth pressure, and geogrid strain. The minor net settlement of the reinforced backfill converges at the early stage of subgrade construction, and the horizontal earth pressure was approximately reduced to the level of 54–63% of the Rankine active earth pressure.

Seismic behavior of piled raft with ground improvement supporting a base-isolated building on soft ground in Tokyo

Vacuum–surcharge preloading is widely used in soft soil foundation reinforcement projects. To study the characteristics of the changes in pore water pressure and settlement of the soft soil foundation as a result of the effect of vacuum–surcharge preloading, in this paper, a consolidation model was established for large–sized sand–drain fluid–solid coupling along the depth direction while taking the sequence of the actual surcharge and vacuum into consideration by using FLAC3D, and a soft foundation’s consolidation process was calculated and analyzed in detail. The results showed the following: (1) the sand drain could be used as a load boundary condition and a vacuum load could be realized by adjusting the pore pressure at the nodes. (2) For the effect of a single vacuum, the settlement and pore water pressure were evenly distributed on the horizontal plane, and the maximum calculated value of the surface settlement was 90.92 cm, but the phenomenon of a “pot–bottom shape” of the settlement and pore pressure gradually became obvious with the increase in the surcharge, and the maximum calculated value of the surface settlement was 153.01 cm. (3) In the numerical calculations, it was found that the pore pressure and settlement distinctly fluctuated once each level of surcharge was applied. The changes in the settlement were basically consistent with the measured values after the adjustment of positive and negative pressure, and the variation trend of the pore pressure was consistent with the measured value. (4) The depth affected by the vacuum could reach at least 16 m. All of these findings are expected to provide references for the calculation of consolidation in vacuum–surcharge preloading.

Influences of train speed on permanent deformation of saturated soft soil under partial drainage conditions

In this paper, an assessment method of excavation disturbance effect is proposed by using distributed optical-fiber strain sensing technique. Model tests of trenchless construction under different parameter conditions are carried out in the laboratory. In the test, the excavation was simulated by using the deflate of pre-burying air bag, soil displacement is measured by settlement mark, at the same time, The soil strain of overburden layer is obtained based on Brillouin Optical Time-Domain Analysis (BOTDA). Through the analysis of the experimental data, the partition theory of excavation disturbance zone is proved and verified through test data. The correlation between ground settlement and soil strain distribution due to trenchless construction are compared and analyzed. The mechanical response of overlying pavement are further discussed. Research results indicate that soil strain of overburden layer is symmetrically distributed about the excavation surface, which is compressed near the centerline and tensioned on both sides due to the excavation disturbance impact. The width of excavation disturbance zone derived from the test data shows good accordance with the calculation results based on the partition theory, the maximum error is less than 10%. A certain consistency exists between the distribution law of strain curve and settlement trough. Due to the uneven distribution of support force caused by foundation settlement, the pavement model shows notable bending deflection after trenchless excavation, and the maximum increment ratio of support force exceed 50%. The combined impact of ground traffic load and excavation disturbance is considered to be more unfavorable to the safety of pavement structure. The conclusions can be suggestive and helpful to trenchless excavation control.

In the projects of buildings and structures, in the last two to twenty-five years, in world practice, the so-called combined pile raft foundation (CPRF) is increasingly used, for which, in the design and calculations, it is assumed that the calculated load from the building is distributed between the piles and the raft, allowing up to 50% inclusion in the work (resistance) of the raft. As part of the scientific and technical support [1-8] of the construction object, instrumental automated monitoring of the stress state of the «soil foundation - combined pile raft foundation» system of the multifunctional complex on St. Pushkinska, 2 in Kharkiv (Ukraine) is carried out. The building has 7 floors and a mezzanine floor, including 2 floors of underground parking, 5 floors of shopping and entertainment area. There is a parking lot on the first 2 floors. The building system is a monolithic reinforced concrete frame with beamless floor slabs. The foundation of the building is a combined pile raft foundation with the centering of bored piles under the load-bearing elements of the frame. The soil base is represented by Quaternary alluvial-deluvial sediments – loams, sands and clays. As part of the implementation of the project, 23 sensors of two types were installed during the zero-cycle construction works: strain gauges (Geosense, England) to determine the stresses in the shafts of bored piles and in the upper and lower grids of the raft reinforcement and soil pressure sensors (Geokon, USA), which were placed under the sole of the raft. The results of the monitoring showed that the actual pressure under the raft does not exceed the pressure from its own weight of the raft (≈25kN/m2), which indicates the absence of inclusion in the work of the raft due to insignificant relative settlements of the combined pile raft foundation. Taking this fact into account when modeling the "base - foundation - structure" system and calculation in the SOFiSTiK showed a qualitative and quantitative convergence of effort values in reinforced concrete structures of a combined pile raft foundation.