Search Results (19)

Post-grouting is an active reinforcement technique that can significantly enhance the bearing performance of bored piles. This study conducted field tests on three in situ test piles using tip grouting, side grouting, and combined tip-side grouting. Based on the analysis of static load test data, the improvement effects of different grouting methods on the vertical bearing behavior of the piles were quantified. In situ tests were then performed to elucidate the reinforcement mechanisms of various post-grouting techniques on the pile foundations. Based on the validated finite element model, the study explored the influence of key grouting parameters on the bearing performance of grouted piles. Analysis of the test data shows that all grouting methods improved the vertical bearing capacity of bored piles. The positive effect of tip grouting was more pronounced than that of side grouting. Furthermore, in the clay layer of the soft soil region, side grouting primarily manifested as splitting grouting, while tip grouting formed a hardened grout bulb at the pile tip through cementation and solidification, thereby significantly enhancing the mobilization of the pile tip bearing capacity. Finite element model analysis shows that, in terms of enhancing the bearing capacity of the pile, expanding the grout diffusion range is more effective than increasing the grout material strength. Full article

Some expressway emergency lanes adopt simplified pavement structures that fail to meet load-bearing requirements after reconstruction. To address the issue of subgrade reinforcement without excavation, a finite element method was employed to analyze the effects of enlarged-borehole grouting (EBG), considering variations in grouting depth and inter-pile subgrade modulus, on pavement load-bearing capacity. Furthermore, field experiments were conducted to evaluate grouting techniques, including enlarged-borehole micro-expansive cement casting (EB-MECC) and enlarged-borehole steel flower pipe split grouting (EB-SFPSG), and three composite grouting schemes. Results indicated that EBG effectively improved the fatigue cracking life of the semi-rigid base layer. Reinforcement effectiveness was positively correlated with grouting depth and subgrade modulus, with the latter exhibiting a more significant influence. Therefore, a 1.5 m grouting depth combined with splitting or compaction is recommended to enhance subgrade stiffness. Field experiments showed that EB-SFPSG effectively enhanced pile–subgrade interaction and mitigated stress concentration around the pile–pavement interface. Comparison of the three composite grouting schemes revealed that both the scheme employing only EB-SFPSG and the hybrid scheme using EB-SFPSG in the middle row with EB-MECC in the side rows exhibited favorable mechanical performance. The latter, however, was achieved at a lower construction cost. Another hybrid scheme that further replaced the middle row with enlarged-borehole conventional pressure grouting (EB-CPG) provided limited reinforcement and poorer uniformity. Full article

In this study, the impacts of various grouting methods and volumes on the vertical bearing characteristics of model piles in clay strata were investigated through indoor static load tests on one ungrouted model pile and two model piles with grouting at the pile tip, as well as two model piles with distributed grouting at the pile tip and along the pile side. These tests were performed in conjunction with data obtained from optical fiber sensors that monitored changes in the internal forces of the pile body. The results indicate that, compared to the ungrouted model pile Z1, the ultimate bearing capacities of the grouted model piles Z2 to Z5 were increased by 83.9%, 175.0%, 125.0%, and 253.6%, respectively. Additionally, the displacements at the pile tops after failure reached 57.6%, 62.3%, 69.5%, and 73.5% that of the ungrouted model pile Z1. These results demonstrate that post-grouting can significantly enhance the ultimate bearing capacity of model piles and reduce settlement at the pile top. Under various loads, the axial force of the pile body decreases gradually with the increasing depth of the pile foundation and increases with the increasing load at the pile top. The increase in the ultimate average side friction resistance and ultimate tip resistance of the grouted model piles (i.e., Z2 to Z5), in comparison to the ungrouted pile, was positively correlated with the grouting volume at the pile tip and along the pile side. All five model piles displayed the characteristics of friction piles. Full article

The implantable capsule grouting pile is a novel pile foundation technology in which a capsule is affixed to the side of the implanted pile to facilitate grouting and achieve extrusion-based reinforcement. This technique is designed to improve the bearing capacity of implanted piles in coastal areas with deep, soft soil. This study conducted model tests involving multiple grouting positions across different foundation types to refine the construction process and validate the enhancement of bearing capacity. Systematic measurements and quantitative analyses were performed to evaluate the earth pressure distribution around the pile, the resistance characteristics of the pile end, the evolution of side friction resistance, and the overall bearing performance. Special attention was given to variations in the lateral friction resistance adjustment coefficient under different working conditions. Furthermore, an actual case analysis was conducted based on typical soft soil geological conditions. The results indicated that the post-grouting process formed a dense soil ring through the expansion and extrusion of the capsule, resulting in increased soil strength around the pile due to increased lateral earth pressure. Compared to conventional piles, the grouted piles exhibited a synergistic improvement characterized by reduced pile end resistance, enhanced side friction resistance, and improved overall bearing capacity. The ultimate bearing capacity of model piles at different grouting depths across different foundation types increased by 6.8–22.3% compared with that of ordinary piles. In silty clay and clayey silt foundations, the adjustment coefficient η_s of lateral friction resistance of post-grouting piles ranged from 1.097 to 1.318 and increased with grouting depth. The findings contribute to the development of green pile foundation technology in coastal areas. Full article

Taking the shield construction of Xiamen Metro Line 2 tunnel side-crossing the Tianzhushan overpass and under-crossing the Shen-Hai Expressway as the engineering background, FLAC3D 6.0 software was used to examine the deformation of adjacent structures based on shield construction parameters in upper-soft and lower-hard strata. The reliability of the numerical simulation results was verified by comparing measured and predicted deformations. The study results indicate that deformation of the pile will occur during the construction of the tunnel shield next to the pile foundation. The shape of the pile deformation curve in the horizontal direction is significantly influenced by the distance from the pile foundation to the adjacent tunnel’s centerline, as well as by soil bin pressure, grouting layer thickness, and stress release coefficient. During the tunnel shield construction beneath the expressway, increasing the soil bin pressure, the grouting layer thickness, and reducing the stress release coefficient can effectively minimize surface deformation and differential settlement on both sides of the deformation joints between the bridge and the roadbed. The practice shows that, by optimizing shield construction parameters in upper-soft and lower-hard strata, the deformation of nearby bridges and pavements can be kept within allowable limits. This is significant for reducing construction time and costs. The findings offer useful references for similar projects. Full article

Mud-protected bored piles are widely used in foundation engineering due to their high bearing capacity and strong adaptability to various geological conditions. However, the formation of mud skin around the pile shaft and sediment at the pile bottom during construction significantly affects their mechanical behavior, posing challenges for performance evaluation and design optimization. The post-grouting technique, which involves injecting grout material to strengthen the bottom and surrounding soils, has been practically adopted to enhance pile performance. This study investigates the effect of construction-induced factors (mud skin and sediment) and post-grouting on the performance of mud-protected bored piles. Finite element analyses were conducted based on a super-long test pile (60 m in length, 1.8 m in diameter) from an infrastructure project in Eastern China. The numerical model was validated against field test measurements and previously published numerical results. The results reveal that mud skin and sediment individually decrease the bearing capacity by 28% and 24%, respectively, compared to ideal conditions. When both factors are present, the bearing capacity is decreased by 36%. The post-grouting technique effectively improves pile performance, increasing the bearing capacity by 81% compared to non-grouting conditions. The findings also demonstrate that side friction dominates the bearing behavior of the studied super-long pile, accounting for approximately 90% of the total bearing capacity. Parametric analysis indicates that post-grouting effectiveness varies with soil properties and dimensions of effective grouting zones, showing greater improvement in weak soils. These results provide insights into the mechanisms through which construction-induced effects impact pile performance and offer guidelines for post-grouting applications. Full article

To investigate the potential application of geopolymer materials in pile foundation post-grouting engineering, this study utilized industrial solid wastes such as fly ash (FA), slag (SL), and steel slag (SS) to prepare geopolymer grouting materials (GGMs) with various mix proportions. The fluidity, setting time, bleeding rate, and mechanical properties of these materials were evaluated to determine the optimal mix proportions for pile foundation grouting. Furthermore, the influence mechanisms of different maintenance conditions on material performance were investigated, including unconfined compressive strength, flexural strength, and microstructural changes. The results indicated that when the SL-to-FA ratio was 1:1, the GGMs satisfied the requirements for pile foundation grouting, and their mechanical properties significantly improved with extended curing time. Under Yellow River water maintenance conditions, the materials formed a dense three-dimensional network of hydrated products, notably enhancing their mechanical characteristics. Additionally, field tests confirmed that GGMs effectively improved the shear strength of the pile–soil interface. The grout distribution pattern on the pile side exhibited a “compaction-splitting” mechanism. These research findings provide theoretical support for applying geopolymer materials in pile foundation grouting engineering. Full article

To investigate the effect of combined end-and-shaft post-grouting on the vertical load-bearing performance of bridge-bored piles in the Dongting Lake area of Hunan, two post-grouted piles were subjected to bi-directional O-cell and top-down load tests before and after combined end-and-shaft grouting, based on the Wushi to Yiyang Expressway project. A comparative analysis was conducted on the bearing capacity, deformation characteristics, and load transfer behavior of the piles before and after grouting. This study also examined the conversion coefficient γ values of different soil layers obtained from the bi-directional O-cell test for bearing capacity calculations. Additionally, the characteristic values of the end bearing capacity, obtained from the bi-directional O-cell and top-down load tests, were compared with the values calculated using the relevant formulas in the current standards, which validated the accuracy of existing regulations and traditional loading methods. The results indicate that the stress distribution along the pile shaft differed between the two test methods. In the bi-directional O-cell test, the side resistance developed from the end to the head, while in the top-down load test, it developed from the head to the end. After combined post-grouting, the ultimate bearing capacity of the piles significantly increased, with side resistance increasing by up to 81.03% and end resistance by up to 105.66%. The conversion coefficients for the side resistance in silty sand and gravel before and after grouting are 0.86 and 0.80 and 0.81 and 0.69, respectively. The characteristic values of the end bearing capacity, as measured by the bi-directional O-cell and top-down load tests, were substantially higher than those calculated using the current highway bridge and culvert standards, showing increases of 133.63% and 86.15%, respectively. These findings suggest that the current standard formulas are overly conservative. Additionally, the measured values from the top-down load test may underestimate the actual bearing capacity of piles in engineering projects. Therefore, it is recommended that future pile foundation designs incorporate both bi-directional O-cell testing and combined post-grouting techniques to optimize design solutions. Full article

Utilizing the results of static load tests using the self-balancing method on two large-diameter bored piles from the Huaiyang Left Line Special Bridge Project of the Lianyungang–Zhenjiang Railway, this study aims to investigate the effect of combined tip-and-side post-grouting on the bearing characteristics of post-grouted piles in railway bridges. The difference in bearing performance between individual piles before and after grouting was evaluated using a comparative analysis. The results show that the bearing capacity of the pile foundations is greatly increased by combined tip-and-side post-grouting. In particular, following grouting, a single pile’s maximum bearing capacity rises from 32.99% to 38.42%. The combined post-grouting produces a compressed grout that enhances the mechanical characteristics of the pile–soil contact, resulting in a significant increase in side resistance all the way along the pile. The combined post-grouting also optimizes the performance of the tip resistance, resulting in a more rapid response as the pile tip displacement increases. Additionally, the combined post-grouting modifies the pile shaft’s load transfer mechanism by increasing the tip resistance’s contribution to the pile foundation’s ultimate bearing capacity and moving the bearing’s center of gravity closer to the pile end. Full article

Drilling with prestressed concrete (DPC) pipe pile is a nonsqueezing pile sinking technology, employing drilling, simultaneous pile sinking, a pipe pile protection wall, and pile side grouting. The unloading induced by drilling, the pipe pile supporting effect, and the dissipation of the negative excess pore-water pressure after pile sinking, all of which have significant effects on the recovery of soil pressure on the pile side, are the main concerns of this study, which aim to establish a method to reasonably evaluate the timing selection of pile side grouting. The theoretical solutions for characterizing the unloading and dissipation of the negative excess pore-water pressure are presented based on the cylindrical cavity contraction model and the separated variable method. By inverse-analyzing the measured initial pore pressure change data from borehole unloading, initial soil pressures on the pile side of each soil layer are determined using the presented theoretical solutions. Then, the presented theoretical solutions were verified through a comparative analysis with the corresponding measured results. Moreover, by introducing time-dependent coefficients α_t1 and α_t2 to characterize the pore pressure dissipation and rheology effects, the effects of the negative excess pore-water pressure dissipation on the pile-side soil pressure recovery are discussed in detail. Full article

To study the applicability of the new geopolymer grouting material for super-long and large-diameter post-grouting bored piles in silty fine sand geology, this paper compares the bearing capacity of two grouting materials, geopolymer and normal Portland cement, and different grouting volume pile side-distributed grouting piles in silty fine sand based on field model tests are analyzed through the diffusion forms of the two materials in silty fine sand through the morphology of the grouted body after excavation. The results show that the ultimate bearing capacities of P0 (ungrouted pile), P1 (8 kg cement grouted pile), P2 (6 kg geopolymer-grouted pile), P3 (8 kg geopolymer-grouted pile) and P4 (10 kg geopolymer-grouted pile) are 5400 N, 8820 N, 9450 N, 11,700 N and 12,600 N, respectively, and that the ultimate bearing capacity of the grouted pile is improved compared with that of the ungrouted pile since, under the same grouting amount, the maximum bearing capacity of the pile using geopolymer grouting is increased by 133% compared with that of the pile with cement grouting. This further verifies the applicability of the geopolymer grouting material for the post-grouting of the pile foundation in silty fine sand. Under the action of the ultimate load, the pile side friction resistance of P1, P2, P3 and P4 is increased by 200%, 218%, 284% and 319% compared with that of P0. In addition, the excavation results show that the geopolymer post-grouting pile forms the ellipsoidal consolidation body at the pile side grouting location, which mainly comprises extrusion diffusion with a small amount of infiltration diffusion, and the cement grouting pile forms a sheet-like consolidation body at the lower grouting location, which primarily comprises split diffusion. This study can provide a reference basis for the theoretical and engineering application of post-grouting piles using geopolymers. Full article

The selection of grouting methods and parameters significantly affects the improvement in the pile-bearing capacity of cast-in-place bored piles. This study proposes a comprehensive set of test methods for constructing model piles, performing grouting at the pile tip and pile side. A series of single-pile grouting and static load tests were conducted using these test methods. The results reveal that pile-side grouting is more effective in controlling pile settlement compared to tip grouting. Furthermore, tip-side-combined grouting exhibits superior reinforcement effects compared to the other two grouting methods. After grouting, a grout bubble is formed at the outlet, consisting of a compact diffusion zone internally and a split diffusion zone externally. Additionally, a vertical diffusion of grout occurs along the pile body, establishing a lateral friction resistance enhancement region. Within this region, the lateral friction resistance of the pile shows a negative correlation with the distance from the grouting outlet. The test results emphasize the significance of grouting volume and its impact on the bearing capacity, settlement control, lateral friction resistance, and grout bubble size in grouted piles, while the influence of variation in grouting pressure in a small range on bearing characteristics is not significantly apparent. Full article

In soft soil areas, to compare the load-bearing characteristics of bag grouting piles and cement mixing piles and study the load-bearing mechanism of bag grouting piles, field tests are conducted in this study, including the comparative compressive test of bag grouting piles and cement mixing piles, and the analysis of pile axial force, pile side friction resistance, and pile end resistance. Moreover, a numerical simulation is developed using ABAQUS 2020 (finite element analysis software) for three-dimensional modeling. The numerical simulation results are compared with the field test results to verify the reliability of the numerical simulation. Furthermore, the influences of five factors are studied; namely, pile length, pile diameter, pile spacing, the thickness of the bedding layer, and grouting pressure are studied for their effects on the compressive bearing characteristics of the bag grouting pile. The results show the following: (1) For composite foundations, bag grouting piles are more effective than cement mixing piles in soft soil areas, and the former provide an 8.8% increase in the bearing characteristics. (2) With an increase in the load, the bag grouting pile experiences greater compression in the middle of the pile body, and the pile side friction resistance is increased; therefore, the pile side friction resistance can be fully developed, and the bag grouting piles have the ability to transfer the load from the top of the pile to the soil at the bottom of the pile. (3) When the external load is maximized, the sharing ratio of pile side friction resistance reaches 96.3%, which shows the excellent frictional performance of bag grouting piles. (4) Among the five factors mentioned above, the most important one is the pile diameter, followed by the pile length and pile spacing, the thickness of the bedding layer, and finally the grouting pressure. The optimal combination in this paper is a pile length of 18 m, pile diameter of 0.4 m, pile spacing of 1.0 m, bedding thickness of 0.3 m, and grouting pressure of 0.6 MPa. Therefore, changing the pile diameter can be given priority during the construction design. The findings in this paper can provide valuable insights and practical experience for the design of similar engineering projects. Full article

Due to soil disturbance during the construction of metro stations, the initial stress of the stratum is modified, leading to ground settlement within a particular range, fracturing the surrounding buildings and even causing significant ground deformation and building collapse. This paper employed the Pile-Beam-Arch method to assemble the Daguanying Station of Beijing Metro Line 7 as the engineering background. The numerical calculation method was used to study the regulations of ground settlement and structural deformation throughout the construction stage. Meanwhile, the effect of surface loading was taken into account and surface settlement control strategies were suggested. Finally, the Stochastic medium theory was used to predict surface settlement. It was evident from the study’s findings that the pilot tunnels excavation and the arches installation accounted for 67% and 23.1% of the total surface settlement, respectively, and produced the most surface settlement. Surface settlement can be significantly reduced by utilizing grouting reinforcement technology and the pilot tunnels excavation approach of “upper first, then lower and side first, then middle”. The structure was much less stressed during the pre-construction stage, with the maximum principal stress ranging from 1 to 5 MPa; after construction was finalized, the maximum principal stress reached 14.203 MPa, concentrating mostly in the middle column part, which was the consequence of the combined action of the upper load and the lower soil uplift. Additionally, there was a linear relationship between the surface load and ground settlement. The bottom slab and the middle column were situated where the structure’s most unfavorable components were concentrated. The conclusions of the surface settlement prediction demonstrated that there were discrepancies between the theoretical calculation and the simulated; thus, the prediction results were more conservative. The study results can serve as a reference for construction sites. Full article

The relationship between pile side frictional resistance and pile tip resistance and settlement is assumed to be ideal elastic–plastic. The load-transfer method is used to analyze the load-bearing characteristics of bored pile in actual projects, and the results are compared with static load test results to prove the reliability of the analysis method and its parameters, on the basis of which the bored piles are reinforced with grouting, namely, pile tip grouting, pile side grouting, and pile tip pile–side composite grouting, are analyzed. The results show that the pile tip grouting mainly improves pile tip resistance and has almost no effect on pile side frictional resistance; the pile side grouting improves pile tip resistance and pile side frictional resistance more significantly; and pile tip–pile side composite grouting improves pile tip resistance and pile side frictional resistance more significantly than the first two. The ultimate load-carrying capacity of the pile is increased by 19%, 49%, and 53% after the use of pile tip grouting, pile side grouting, and composite grouting respectively. Full article