Post-grouting Pile Research Articles

Field investigations on bearing characteristics of composite post-grouting piles in clastic rock layers

Field investigations on bearing characteristics of composite post-grouting piles in clastic rock layers

Study on Vertical Bearing Capacity of Pile Foundation with Distributed Geopolymer Post-Grouting on Pile Side.

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.

Experimental Study on Post-Grouting Pile Vertical Bearing Performance Considering Different Grouting Methods and Parameters in Cohesive Soil

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.

Experimental Investigation of Vertical Bearing Characteristics of Composite Post-grouting Piles in Sandy Soil

Experimental Investigation of Vertical Bearing Characteristics of Composite Post-grouting Piles in Sandy Soil

Experimental Study on Grouting Effect of Combined Post-Grouting Piles in Cohesive Soil

Abstract To study the grouting effect of pile end and pile side combined post-grouting technology in cohesive soil, the self-balancing static load test was carried out on two bored piles with length of 56.5 m and diameter of 1.5 m in a bridge pile foundation project, and the test results before and after the combined cement grouting were compared and analyzed. The influences of combined grouting on ultimate load-bearing ability, pile axial force, pile side friction, pile end resistance, and settlement reduction of bored piles in cohesive soil were studied. The findings revealed that the ultimate load-bearing abilities of combined grouting piles in cohesive soil improved by 32.99∼38.42 % as compared with before grouting, the corresponding settlement was effectively controlled, and the grouting effect was remarkable. Combined post-grouting enhanced the soil layer strengths of pile tip soil and pile side soil, improved the condition of pile-soil contact surface, and greatly increased the pile end resistance and pile side friction. The pile end resistances increased by 96.90∼98.61 % and pile side frictions increased by 23.63∼29.70 %, which causes the pile axial force to decay faster along the piles and also has an obvious influence on load transfer characteristic of the test piles. However, in some stages, the reinforcement effect of post-grouting on the soil stiffness of pile side was not obvious or even deteriorated, which reflected the instability of the reinforcement effect of post-grouting technology.

Evaluating the effect of post-grouting on long bored pile based on ultra-weak fiber Bragg grating array

Fiber optic sensing has been widely acknowledged as a dependable tool to monitor pile performance. However, its applicability is restricted by the limited multiplexing capacity of fiber Bragg gratings (FBG) or the high equipment cost and poor real-time performance of distributed fiber optic sensing systems. In this paper, a novel sensing cable and system were developed based on ultra-weak FBG array for strain measurement of large-scale engineering structures. Through the laboratory calibration and field test of a post-grouting pile, the good strain measurement performance of the sensing cable and system were confirmed. Based on the distributed strain data obtained by the UWFBG array, the strengthening mechanism of the pile was well explained. The UWFBG array and sensing system could realize distributed, high-precision, and real-time strain measurement with a spatial resolution of 1 m within 1.5 km, which has great potentials in the monitoring of geo-environment and engineering structures.

Effects of soil unloading and grouting on the vertical bearing mechanism for compressive piles

The present study conducts a series of model cast-in-place piles tests to analyze the vertical bearing characteristics and the grout returned diffusion mechanism along the pile shaft of tip post-grouting piles with different grouting and pile shaft soil unloading conditions. The model test results show that the pile tip post-grouting technology can improve the weak difference in the bearing characteristics and axial force distribution of the pile foundation caused by pile shaft soil unloading. The pile shaft resistance can be improved by the returned grout in the pile shaft. The pile shaft resistance will mainly bear the pile top load when the pile top load and the grouting volume are relatively small, and the pile tip resistance will mainly bear the pile top load with the increases of the pile top load and the grouting volume. The grouting return height increases with the increase in pile shaft soil unloading degree, and the analyzed values of the grouting returned height based on the pile bearing characteristic results are close to the measured values. The grouting diffusion mechanism of the cement on the pile tip and pile shaft soil during the pile tip post-grouting process is revealed.

Study on the Application of Elastic Wave CT Technique to Detect the Effect of Post-Grouting of Pile Foundation

The post-grouting technology can effectively improve the bearing capacity and reliability of foundation piles, and it is of great academic and economic significance to evaluate the effect of post-grouting. However, in general, the evaluation of the effect of post-grouting slurry on foundation piles is still relatively single, and most researchers only test the improvement of the bearing characteristics of post-grouting piles, but there are few research results on the distribution state of slurry consolidation and the range of the reinforced soil. In this paper, elastic wave CT was used to detect the bridge piles of Taizhou Bay Du Xiaipu Bridge, and elastic wave CT technology was applied to the detection of the post-grouting effect of foundation piles experimentally. The spatial distribution characteristics of the underground grouting reinforcement area were revealed from the perspective of visualization, and the influencing factors of the elastic wave inversion results were analyzed. The conclusions obtained from elastic wave CT detection were similar to those of electromagnetic wave CT, and the laws are basically consistent with the current engineering experience, reflecting the applicability of using elastic wave CT to detect the effect of post-grouting of pile foundation.

Full-scale field test study of bearing characteristics of post-grouting pile for offshore wind turbines

Full-scale load tests were conducted on a combined steel pipe and bored pile foundation used for offshore wind turbine in Fuqing Xinghua Bay. Due to the complex geological conditions of the project, lengthening the bored pile will cause it to exceed the steel pipe pile so much that there are construction risks such as collapsed holes, hence, combined tip-and-side post-grouting was used to improve the bearing characteristics of the pile foundations. The results of double-level O-cell bi-direction tests before and after grouting on test pile SZ32 are reported. Comparing the test results before and after grouting shows that post grouting can significantly enhance the bearing capacity of the pile foundations. Furthermore, the relative displacement required to mobilize the shaft resistance of the test pile is significantly reduced by the post grouting craftwork. Additionally, the core samples obtained from the coring tests showed that the cement grout was distributed from 0.5 D below the pile tip to 5.3 D above the pile tip, respectively. Finally, the results could be applied to similar foundation design used in offshore wind turbine.

Analysis of Grout Diffusion of Postgrouting Pile Considering the Time-Dependent Behavior of Grout Viscosity

Abstract To get an accurate bearing capacity of a postgrouting pile, the range of grout diffusion should be considered in practice. Considering the time-dependent behavior of power-law cement grout...

Centrifugal model test of post-grouting pile group in loess area

In this paper, based on the in-situ post-grouting single pile of the Wuqi-Dingbian Expressway in China, the bearing performance of the post-grouting pile groups in loess area were studied with the use of the centrifugal model test. Taking into consideration pile spacing and number of piles, nine working conditions of single pile, 2 × 2 pile group with different pile spacing and 3 × 3 pile group were designed. The settlement, ultimate bearing capacity, pile side resistance, and end resistance ratio of pile groups with different pile spacing and number of piles before and after grouting were compared and analyzed. Finally, based on the change in the group efficiency obtained before and after grouting through the model test, the group efficiency of non-grouting pile groups in code was modified and applied to the calculation of the ultimate bearing capacity of the grouting pile groups. The results show that the group efficiency will decrease after grouting, and the bearing capacity of grouting pile groups increases gradually with the increase of pile spacing, and reaches the maximum when the pile spacing is 5d. The proposed bearing capacity calculation method of grouting pile group was validated by the model test results, and the calculation results generally agree with the model results, which is valuable for pile foundation designs.

Application of Fiber Bragg Grating Sensing in Bidirectional Tests of Pile Foundations

Abstract The fiber Bragg grating (FBG) technique has emerged as a new strain monitoring technique in civil engineering applications. In this paper, based on the principle of the FBG technique and the bidirectional test method, FBG sensors and conventional vibrating wire strain gauges (VWSGs) were employed to monitor the strain variation law of a pile under different loads and analyze the relationship between the side resistance and pile-soil relative displacement of soil layers in bidirectional field testing of a large-diameter cast in situ pile. Four field bidirectional test cases of cast in situ piles, prestressed high-strength concrete (PHC) and steel pipe pile, and pile-base post-grouting pile are presented. The applicability and stability of the FBG sensing technique were verified by analyzing the side resistance distribution and bearing capacity. The results showed that FBG sensors can remove the influence because of residual force and the effect of temperature change and concrete expansion photosensitive material provides an improved sensitivity to the external environment compared with a VWSG. The strain and side resistance variation tendency of the cast in situ pile were consistent between the two kinds of sensors. The FBG sensing technique had high test accuracy in the four bidirectional O-cell field test cases of the cast in situ pile, PHC and steel pipe pile, and pile-base post-grouting pile. The pile-base post-grouting technique is an effective procedure that was implemented to increase the ultimate bearing capacity. The research results of this paper reveal a new strain monitoring technique for the bidirectional test method of pile foundations and represent a new test method for measuring the bearing capacity of PHC and steel pipe piles that has a remarkable application value in practical engineering.

Research on Bearing Capacity of Post-grouting Super-long Bored Pile

The bearing capacity of the post-grouting super-long bored pile, calculated by the standard enhancement coefficient, is 66% larger than that of the measured. The FEM analysis shows that when the grouting radius at the pile end is 1.5 d and the permeating height of the cement slurry is 4.05 m from the pile end, the end resistance enhancement coefficient is 1.17, and the pile side average friction resistance enhancement coefficient is 1.31 within 12 m above the pile end. The calculated bearing capacity is close to the measured bearing capacity of the post-grouting pile by those enhancement coefficients. The calculation shows that: a) in the case of no grouting, the pile end reaction force is about 5.78% of the pile top load; b) in the case of grouting, when the grouting diffusion radius at the pile end is 1.5 d and the permeating height from the pile end is 4.05 m, the post-grouting pile end reaction force is about 6.78% of the pile top load; and c) after grouting, the load transmitted to the pile end cannot be significantly increased; d) using the reinforcement coefficient suggested by the Standard, the calculated bearing capacity is larger than the measured.

A practical method of calculation of bearing capacity and settlement of large- diameter post-grouting piles

A practical method of calculation of bearing capacity and settlement of large- diameter post-grouting piles

Calculation and analysis of bearing capacity reliability index of post-grouting pile

The bearing capacity of bored piles is significantly improved and the dispersion of bearing capacity is reduced obviously by employing the method of grouting. However, there is still a lack of systematic research on the calculation and analysis of the reliability index of post-grouting pile. In this paper, the static load test data of 152 non-grouted bored piles and 113 post-grouted bored piles are collected. The influence of factors such as safety factor K, types of load effect combination, and the pile diameter are taken into account. Then, the approximate probability method based on the first-order second-moment method (JC method) and Monte Carlo method is employed to analyze the reliability indexes of post-grouted bored piles and non-grouted ones.

Laterally Loading Experimental Study of Bearing Capacity Characteristics of Large-Diameter Bored Cast-in situ Deep and Long Pile

Base on the laterally static load and pile stress testing results of three kinds of different construction technology piles (post-grouting pile, expanded branches and bells by 3-way extruding arms, squeezed branch piles) in Tangshan LNG tank area, the distribution law of pile top deformation, moment and shear was analyzed under laterally load. The test results showed that: The H–Y0 curves of three different construction technology piles have no significantly the inflection point and have same deformation law; H–△Y0/△H curve show three stage: elastic stage, elastic–plastic stage and failure stage. The critical load value and ultimate load value of three different construction technology piles is same; The distribution rule of three piles’ moment increases firstly and then decreases with the pile depth, the support plate (fork) that is set the lower pile position has little effect of the top pile load and the bending moment; The relationship of foundation soil horizontal resistance force’s ratio coefficient (m) versus laterally load and pile top displacement are nonlinear, the curve of m and mud surface displacement (Y0) is fitted by exponential equation and m value corresponding to pile top displacement is gained, the design basis is provided for engineering design.

Optimization Analysis of Settlement Parameters for Postgrouting Piles in Loess Area of Shaanxi, China

The settlement calculation of postgrouting piles is complex and depends on the calculation method and parameters. Static load tests were conducted to compare the settlement characteristics of nongrouting and postgrouting piles, and three vital parameters in the layer‐wise summation method were revised to predict the settlement of postgrouting piles. The elastic compression coefficient was deduced based on the Mindlin–Geddes method by considering the influence of the change in the pile side resistance distribution and end resistance ratio on the elastic compression after grouting. The relationship between the compression modulus and soil gravity stress and cone penetration resistance were established, respectively, using experimental data. The optimum value of the settlement empirical coefficient was determined using regional data. Finally, we used the postgrouting pile of the Wuqi–Dingbian expressway as a practical example. The results obtained from the layer‐wise summation method after parametric optimization were close to the measured values. The results of this study provide reference data and guidance for the settlement calculation of postgrouting piles in this area.

Field study on post-grouting effects of cast-in-place bored piles in extra-thick fine sand layers

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.

Experimental Study on Post Grouting Bearing Capacity of Large Diameter Bored Piles

Post grouting can improve the inherent defects such as the formation of the mud cake at pile side and the sediment at pile end in the process of bored pile construction. Thus post grouting has been widely used in Engineering. The purpose of this paper is to research the influences of post grouting to pile bearing capacity more systematically and intuitively. Combined with the static load test of four test piles in Weihe River Bridge test area of new airport highway in Xi’an, the bearing capacity and settlement of routine piles and post grouting piles are comparatively analyzed. The test results show that under the same geological condition, post grouting can improve the properties of pile tip and pile shaft soil of bored piles significantly, enhance the ultimate resistance, improve the ultimate bearing capacity and reduce the pile tip settlement. Then post grouting can aim to optimize pile foundation.

Mechanism Research on the Improvement of Bearing Capacity of Single Pile by Pile-base Post Grouting Technique and Estimation of Bearing Capacity

The slurry wall bored grouting has some defects. The pile-base post grouting technique can effi- ciently make up these defects and greatly improve the bearing capacity. Based on the pile-base post grouting technique and its process analysis, this paper carries out a detailed analysis about the improvement of mechanism of bearing capacity and mechanism of spherical expansion by the use of pile-base post grouting technique, as well as the estimation method of the bearing capacity of pile-base post grouting pile, which has a certain refer- ence value for theoretical research and technical application of the technique.