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Pile foundation is an effective technique to support buildings in the presence of soft soil and seismic areas. More recently, the rigid inclusions system has also been utilized for founding buildings. Both systems increase the bearing capacity of the soil and allow reducing the total and differential settlements in the structure. However, the study of these systems in a complete and accurate way implies the consideration of the soil–structure interaction (SSI). In order to investigate the impact of different pile toe conditions (including the placement on hard soil, an anchorage and floating piles) in the response of mid-rise buildings, numerical models with a 5-storey frame building founded on the inclusions system (soil–inclusion–platform–structure) are analyzed and compared with the pile system (soil–pile–structure). Fully coupled finite difference numerical models were developed using Flac 3D. The influence of the dynamic characteristics of the structure was considered analyzing buildings with different heights (3 storeys to 7 storeys). The linear elastic perfectly plastic model with a Mohr–Coulomb failure criterion is used to represent the behavior of the soil. Values of the maximum lateral displacements, of the inter-storey drifts and of the shear forces distribution in the buildings, as well as the rocking of the foundation, are presented. Concerning the foundations, efforts and displacements are compared for the different systems. The results show that the type of support condition influences the seismic response of the building and the efforts and displacements in the rigid elements, depending on the foundation system. The efforts at the toe level in the rigid elements are highly influenced by the support conditions, but there is only a slight influence from the head connection.

A new type of static load test system and test method based on steel screw anchor pile is proposed. Through field uplift tests of single pile and pile group, the influence of soil properties, pile length and other factors on the uplift bearing capacity of steel screw pile is analyzed. The influence range of steel screw pile on the displacement of adjacent soil and pile foundation are revealed. The calculation method of ultimate uplift bearing capacity of single steel screw anchor pile is established. The reliability of the test method is verified by practical cases. The test results show that the uplift bearing capacity of steel screw pile is higher than that of straight rod pile. According to the properties and compactness of the soil, the coefficient of uplift side resistance improvement of steel screw piles can be taken as 1.2 – 1.6. The construction of steel screw pile is convenient and can be reused, without special treatment of the test site. The test method can save up to 70% of the cost compared with traditional surcharge test method, and greatly improve the safety of large-tonnage static load test.

The post-pressure grouting technique has proven to be an effective method to enhance axial resistance. In this paper, field tests were conducted to investigate the performances of large-diameter cast-in-place bored piles for six combined side-and-tip grouting piles and two side-grouting piles in extra-thick fine sand layers. The load–displacement response, shaft resistance, and mobilization of unit base resistance were discussed. The field results indicate that compared with the piles before post-grouting both the shaft resistance and base resistance for the piles after post-grouting are significantly improved. The piles after post-grouting have higher load-bearing capacity. Meanwhile, the load-bearing capacity of combined-grouting piles is also greater than that of side-grouting piles. Additionally, the strengthening effect of the surrounding soil improvement due to side grouting on the base resistance can enhance the unit base resistance, and the unit shaft resistance can also be increased by the soil improvement at the pile tip due to tip grouting. Moreover, the distribution of the injected pressurized grout at the pile tip and side is detected by an electromagnetic wave computerized tomography (EWCT) technique. The results reveal that EWCT can detect the distribution pattern of the pile, injected grout and geotechnical interface and evaluate the diffusion range of the grout of the soil at the pile tip and side, which can be used to assess the grouting effect of grouted piles. Finally, an in situ standard penetration test is employed to evaluate the grouting effect of grouted pile by variation of the SPT N value before and after post-grouting. The research results have reference value and guiding significance for the design and effect detection of post-grouting piles.

In-situ lateral load tests were conducted on rectangular piles in gravelly soil before and after grouting to investigate the impact of combined side and end grouting on lateral bearing capacity and the failure mode of pile-soil interaction. The results indicate that this combined grouting technique significantly enhanced the lateral bearing capacity of the pile, achieving a 30% increase compared to before grouting. After grouting, the bonding state between the pile and the soil improved, resulting in the formation of tension-shear cracks within the soil on the side of the pile under lateral load. The load-displacement curve of the rectangular pile exhibited nonlinearity, with the deflection deformation showing the load characteristics of an elastic long pile. The bilinear model can accurately assess the actual bearing capacity of the rectangular pile. Comparing the theoretical model predictions with the experimental data, the prediction errors were −3.5% and 1.8% before and after grouting, respectively.

In order to solve the technical problem of using steel sheet piles in soft soil foundations of deep water docks, the use of grid type cement mixing pile walls to reinforce the in-situ soft soil behind steel sheet pile docks is a new type of composite structure attempt. This paper combines practical engineering and uses finite element analysis software to study the vertical displacement, vertical stress, and horizontal displacement changes of reinforced soil in three layout forms: non-mixing pile structure, grid type cement mixing structure, and dispersed mixing pile structure. The results show that the grid type cement mixing pile structure can reduce soil settlement, improve the stability of reinforced soil, and reduce lateral soil pressure on steel sheet piles compared to the non-mixing pile structure and the dispersed mixing pile structure. In the practical application of steel sheet pile wharf engineering, the use of grid type cement mixing piles can improve the stability and engineering benefits of the wharf structure.

The grouted gravel pile is a new method of pile foundation, which has been widely used in engineering fields in recent years. However, the grout diffusion characteristics and full-field displacement response of soil during grouting have not been fully revealed and systematically studied in previous publications. This paper employed a transparent soil model test system to explore the effects of the grouting pressure (GP), soil pre-consolidation pressure (SPCP), and initial viscosity of grout (GIV) on the grouting performances and load-bearing characteristics of grouted gravel piles. The development laws of the grouting duration, displacement field of the soil, and ultimate load-bearing capacity of the pile were analyzed. The results show that the total grouting duration decreases with a higher GP, increases with the increasing GIV, initially increases and then decreases as SPCP increases. Both the range of horizontal and vertical displacements of the soil around the pile and the distribution of vertical displacements of the soil at the pile end were obviously enlarged with GP as well as with GIV. However, with the increasing SPCP, they showed a decreasing tendency. The vertical ultimate load-bearing capacity of the grouted gravel pile increases with GP, SPCP, and GIV to varying degrees. The findings of this study contribute to the understanding of the pile-soil interaction during grouting process of the grouted gravel pile, which may improve the design of construction parameters.

The primary objective of this study is to establish an innovative theoretical framework for analyzing the behavior of an end-bearing pile-supported embankment. This proposed methodology extensively investigates various aspects, including the characteristics of relative slip at the interface between the pile and soil, the distinctive non-uniform deformation patterns typically observed in soft soils, and the substantial influence of pile–soil interaction on the evolution of soil arching phenomena. To precisely capture the frictional relationship and relative displacement within the pile–soil system, we introduce an enhanced ideal elastic-plastic model. Additionally, a deformation function is incorporated to simulate the non-uniform deformation of soft soils, and an improved soil arching model is developed to assess its impact on the overall behavior. The analytical solution is derived through the implementation of a stress and volume deformation continuity condition, and its validity is effectively demonstrated through numerical simulations. The results indicate that under the load of the embankment, relative slip at the pile–soil contact surface is a significant phenomenon and should not be neglected in theoretical calculations. The relative displacement between the pile and soil initially exhibits a linear relationship with depth, and later follows a quadratic function as depth increases.

The Helix Stiffened Cement Mixing (HSCM) piles are a type of composite pile with peripile hydraulic soil formed by simultaneous grouting during the installation of helical piles. Combining the grouting process with the helical pile increases pile stiffness, improves axial bearing capacity, addresses buckling and corrosion issues of the pile body, and enhances pile skin friction, thereby increasing its bearing capacity. Currently, there has been extensive research on the bearing capacity of HSCM piles in clay soil, but less on their bearing performance in sandy soil. This study investigated the effects of the number of helix plates, grouting pressure, and the location of grouting holes on the axial bearing performance of HSCM piles through laboratory model tests. The pile formation process, load–displacement curve, variation in pile diameter, and load transfer mechanism of each test pile were analyzed. Using a parametric analysis of numerical simulations, the influence of a sandy soil foundation on the bearing capacity of HSCM piles under varying internal friction angles was examined. The results indicated that grouting holes positioned below the first layer of helix plates enhanced the axial bearing performance of HSCM piles; additionally, increasing the number of helix plates and grouting pressure appropriately also enhanced the axial bearing performance and increased the pile body diameter, positively affecting the pile formation. Additionally, HSCM piles functioned as friction end-bearing piles in sandy soil, with the vertical load at the top of the pile primarily borne by pile end resistance at the limit state of bearing capacity. With increasing internal friction angles and dilation angle, the bearing capacity of the pile foundation exhibited a rising trend.

A systematic study into the behavior of reinforced semi-rigid piles in response to lateral monotonic and cyclic loading in clay was performed with centrifuge modeling tests (100×g). The aim was to investigate the pile–soil interaction mechanism of reinforced semi-rigid piles and to give some generally applicable design advice for reinforcing semi-rigid piles with cement-improved soil. For monotonic loading, the overall load–deflection behavior, profile of bending moment, net soil pressure and pile deflection have been fully studied, in addition to the p–y curves and excess pore pressure response of reinforced and unreinforced piles. It is found that shallow cement-improved soil reinforcement can greatly improve the lateral capacity of piles. In addition, a hyperbolic tangent model was proposed to fit the p–y curves obtained from monotonic tests for reinforced and unreinforced piles. For cyclic loading, it was found that compared with unreinforced piles, reinforced semi-rigid piles reduce the accumulation of pile deflection and the degradation of stiffness. The trends of the cyclic bending moment and cyclic p–y curves are also revealed. A series of supplementary finite element analyses were conducted to study the effects of reinforcement parameters (reinforced width, reinforced depth and strength of cement-improved soil) on lateral pile capacity. It is suggested that shallow reinforcement with a reinforced width of 5D and a reinforced depth above the rotation point of a semi-rigid pile is both economical and practical.

The Helix Stiffened Cement Mixing (HSCM) pile is a composite of a rigid helical pile and a flexible cement soil pile. These two types of piles are constructed simultaneously to form a strong composite pile with complementary enhancement. Based on existing field tests, this paper systematically designs indoor tests for HSCM piles. It considers the effects of rotational speed, drilling speed, grouting water-cement ratio, the number of helical blades, and grouting pressure process parameters, and analyzes their impacts on the pile formation and the strength of the surrounding cement soil. The results show that increasing the rotational speed during HSCM pile formation can substantially improve the uniformity of the surrounding cement soil strength. A significant increase in drilling speed can lead to a decrease in the cement content of the pile, thereby reducing its diameter and strength. The diameter of HSCM piles increases as the water-cement ratio decreases, with the trend slowing when the ratio is less than 0.7. Increasing grouting pressure can significantly increase the diameter of pile formation and the strength of the surrounding cement soil. An appropriate increase in the number of blades can improve the integrity and continuity of the hydromud pile. Additionally, increasing the number of helical blades can enhance the uniformity and integrity of the pile, thereby improving the bearing performance of the pile foundation. This paper provides a parametric design basis for the construction of HSCM piles in marine soft soil sites.