A series of large-scale shaking table tests were carried out to investigate the seismic performance of different cement-soil reinforced pile groups in liquefiable sands. Specifically, sinewave scanning was performed on three cement-soil reinforced 3 x 3 pile groups and one conventional (unimproved) 3 x 3 pile group. In this study, the bending moment of group piles, the horizontal displacement of the superstructure, pore water pressure into soils, and the settlement and acceleration response of piles and the ground under different earthquake intensities were recorded. The natural frequency of the ground and the dynamic stress-strain relationship of the soils around piles were obtained. The results show that the acceleration response of the improved pile groups before soil liquefaction is significantly smaller than that of the unimproved pile group. However, the acceleration attenuation of the unimproved pile groups after soil liquefaction is substantially greater than that of the improved pile group. In addition, the lateral displacement of the superstructure, the settlement of pile heads, the bending moment of pile shafts, and the dynamic shear strain of the soils around piles in improved cases are all smaller than those in the unimproved case. In particular, the improved cases significantly suppressed the pile bending moment at the interface between the liquefied layer and the non-liquefied layer. The spatial layout of cement-soils significantly impacts the natural frequency and stress changes of the pile-soil Winkel elastic foundation beam systems.
In soft soil environments, deep foundation pit excavation often leads to significant surface settlement, lateral displacement of support structures, and uneven settlement of surrounding buildings due to the complex geotechnical conditions and the inherent characteristics of soft soil, such as high compressibility and low shear strength. This study systematically analyzes 23 deep foundation pit excavation cases from Ningbo city, located in a silty clay region, to examine the deformation behavior during excavation. The research focuses on the impact of key factors such as excavation depth, pit dimensions, support structure parameters, and soil characteristics on the deformation of diaphragm walls. The results show that the maximum lateral displacement of diaphragm walls ranges from 0.09 to 0.84% of the excavation depth, with an average value of 0.36%. Deeper excavations lead to greater lateral deformation due to increased soil pressure and pore water pressure, with the maximum displacement typically occurring at 1.0-1.3 times the excavation depth. Soft soil thickness significantly amplifies wall deformation, with the displacement ratio increasing linearly with the ratio of soft soil thickness to wall depth. Increased wall stiffness, embedment depth, and support system stiffness effectively reduce lateral displacement. These findings provide a quantitative basis for optimizing diaphragm wall design and support systems to mitigate deformation risks, offering valuable guidance for deep foundation pits in similar soft soil environments.
The excavation of the deep foundation pit of subway station may cause excessive deformation of foundation pit and retaining structure and then pose a threat to the safety of surrounding buildings and people. Therefore, it is necessary to analyze the characteristics of ground settlement and lateral displacement of the retaining system of foundation pit caused by deep foundation pit excavation in the Guangzhou composite stratum. Based on 28 subway station projects in Guangzhou, this paper analyses the monitoring data in the process of deep foundation pit excavation and reveals the deformation characteristics of subway deep foundation pit in the Guangzhou composite stratum. The research results can provide data support for the excavation scheme design and environmental control of similar deep foundation pit projects. The results show that: (1) The final deformation of the foundation pit at Guangzhou Metro Station is predominantly within the range of 5 to -15 mm. Monitoring points with settlement values exceeding 30 mm constitute the smallest proportion, while only a limited number of measuring points exhibit surface uplift. The observed ground uplift can be attributed to two primary causes: basement heave and the infiltration of grouting slurry outside the pit. (2) The maximum ground settlement of foundation pit increases with the increase of excavation depth. When the aspect ratio of foundation pit is greater than 15, the maximum ground settlement has an obvious positive linear relationship with it. The insertion ratio of foundation pit retaining structure in the Guangzhou area is mainly concentrated in 0.30-0.59, with an average value of 0.42, and the maximum ground settlement gradually decreases with the increase of insertion ratio. (3) The maximum lateral displacement of the retaining structure of the foundation pit accounts for the largest proportion in the range of -20-25 mm. The maximum lateral displacement of the retaining structure increases with the increase of the excavation depth and the length-width ratio of the foundation pit. The maximum lateral displacement of the retaining structure decreases with the increase of the insertion ratio. There is an obvious skirting phenomenon in the granite residual soil foundation pit. Attention should be paid to and the insertion ratio should be appropriately increased in the project. (4) The maximum ground settlement caused by deep foundation pit excavation of a subway station in the Guangzhou area is 0.99-1.90 times of the lateral displacement of foundation pit retaining structure.
The rigid and fixed diaphragm wall (RFD) is a novel strut-free retaining wall system. This system needs a rigid connection between diaphragm panels. However, in Indonesia, constructing the rigid connection between diaphragm wall panels is scarce. The main objective of this study is to investigate the effectiveness of the RFD system on lateral wall deflection and excavation stability considering anisotropic factors due to joints in the diaphragm wall panels. First, the soil and structure parameters of the three-dimensional finite element model were validated through a well-documented braced excavation case history, which is located in Central Jakarta. Then, the RFD system was introduced to the 3D model. Some parametric studies were also conducted by varying several parameters to understand their influence on safety factors and wall deflections. The analysis results indicate that the implementation of the RFD system yields positive outcomes in controlling lateral deformations. The length of buttress walls and the use of cap slabs significantly affect excavation deformations and safety factors, while the depth of cross walls and buttress walls has a less significant impact. The presence of joints in the diaphragm wall panels causes the wall to be anisotropic, resulting in a reduction in wall stiffness. The reduction in wall stiffness leads to an increase in lateral wall deformations and a decrease in the excavation safety factor.
To research the effect of vertical earthquakes on rectangular underground structures in inclined liquefied foundations, and explore the seismic response characteristics of the structure with bidirectional earthquake, the finite element-finite difference coupled numerical method is used. The results revealed that the vertical earthquake will increase the degree of soil liquefaction in the vicinity of the structure and the dynamic response of the structure. The influence is related to the type and amplitude of the seismic wave. The displacement of the subway station will increase gradually as the compactness of the sand decreases or the angle of inclination of the ground increases. The lateral displacement of the subway station mainly occurs during the earthquake, and the vertical displacement mainly occurs after the earthquake. In addition, in the inclined site, the vertical displacement and internal force of the left and right sides of the underground structure and the excess pore water pressure ratio of the soil are not symmetrically distributed along the central column, and the closer to the bottom at the slope, the larger the settlements of the structure produce to make the whole structure rotate. The study can provide some seismic strengthening suggestions for underground structures in the inclined liquefiable site with bidirectional earthquakes. The seismic design of underground structures also needs to take into account the effects of the structure rotation during an earthquake in the inclined liquefiable site.
The absence of a defined allowable pile ductility in integral abutment bridges (IABs) creates a critical gap in determining the maximum safe bridge length. This paper introduces a design aid procedure to assist bridge engineers in establishing the length limits of jointless bridges. Numerical and analytical approaches were used in formulating the design aid procedure. A total of 66 finite difference models were established to obtain pile equivalent cantilever length considering various design parameters (soil stiffness, pile size, pile orientation, axial compressive load, and lateral displacement magnitude). The analytical approach incorporates a strain compatibility and equilibrium model to generate moment -curvature diagrams and load -deflection curves for standard HP sections commonly used in IABs construction. The validity of the developed design aid procedure was examined and tested with available experimental and numerical results. Lateral buckling displacement capacity of HP sections ranged from 50 to 100 mm (2 - 4 in.). Based on these displacement capacities, length limits for IABs were established and compared with existing studies. The maximum length limits for steel integral bridges fall within the range of 162 - 320 m (530 - 1050 ft), while concrete integral bridges have limits ranging from 210 to 390 m (680 - 1285 ft). These limits depend on factors such as pile size, soil stiffness, and climate conditions.
Jet grouting piles were widely employed for ground reinforcement in building and infrastructure engineering due to the low cost and construction convenience. However, this foundation treatment method is not allowed to be used in high-speed railway involved constructions in China because of the concerning of the negative effect on the lateral displacement of the existing high-speed railway. To find a reasonable application distance of jet grouting piles away from existing high-speed railway bridge in deep soft soils with medium sensibility, a series of laboratory and in-situ tests on the influence of the jet grouting piling on the deformation of surrounding soils and adjacent high-speed railway bridge are carried out. The geological characteristics of the construction site and the mechanical properties of the soft soil are deeply investigated by utilizing field and laboratory tests. The piling induced lateral displacement of the surrounding soils is monitored as well as the displacement of an adjacent high-speed railway bridge. The monitoring data reveal that the influence area of the jet grouting piling is approximately 1.75 -1.85 times of the pile length in deep soft soils. The critical distance of the jet grouting piles from the existing high-speed bridge should be larger than 2 times of the pile length.(c) 2023 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY -NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).