Pile End Research Articles

Thermal performance of wedge pile slab foundation without frost protection insulation and highly insulated slab on ground floor – first year measurements

In the Nordic countries frost insulation is necessary if the foundation is above the frost-free depth. The thermal performance of the pile foundations is between a shallow ground foundation and a frost wall foundation. The pile ends extend below the frost line to help insulate the ground beneath a building’s foundation. The ends of the piles extend below the frost line to prevent the foundation of the building from frost heaving. However, there may be a risk that the ground below the slab on ground may freeze and frost heaving may occur there. The risk of frost below the slab on ground floor and/or basement increases because increasing thickness of floor insulation remarkable influences frost insulation dimensioning. In this study a 6.5 × 17-meter size uninsulated wedge pile slab foundation with highly insulated (U=0.07 W/(m2·K)) slab on ground floor was constructed for a heated building and equipped with temperature, soil moisture, relative humidity, and heat flux sensors. Seven temperature measurement piles below the building and one for reference 8 meters far from the building reached a depth of up to 3.2 meters, which is deeper than the usual 1.4 m depth to avoid freezing in foundation design. In three places, the temperature below the insulation of slab on the ground is measured at 0.5 meters step up to 3 meters from the outer wall of the building. The first-year measurement results showed that temperature did not drop below the zero degree below the foundation and floor. Even though during winter the daily average absolute minimum temperature was -24 °C the sum of degree hours below the zero degree was -7300 °Ch. The historic 50-year absolute sum of minimum degree hours below the zero degree was -28600 °Ch. In addition to real measurement results this three-dimensional temperature sensor field helps to calibrate and validate dynamic model for temperature simulation of thermal performance of wedge pile slab foundation without frost protection insulation and highly insulated slab on ground floor.

Effect of Solidified Depth on the Vertical Compressive Bearing Characteristics of the Soil Continuously Solidified Pile Group Foundation

To meet the ultra-high bearing capacity design requirements of pile foundations under geological conditions without a good holding layer, we invented a new type of group pile foundation with the soil continuously solidified between piles (hereinafter referred to as the SCS group pile foundation). Considering the solidified depth as a key influencing factor, the vertical ultimate compressive bearing capacity, load transfer law, and damage pattern of the soil around the continuously solidified group pile foundation were investigated using an indoor half-model test. The results revealed that the setting of the continuously solidified part has a significant effect on its compressive bearing characteristics. The ultimate compressive bearing capacity of the SCS group pile foundation was increased by four to nine times compared with the traditional group pile foundation. When the pile spacing is 4–6D (D = pile diameter), designing a continuously solidified depth greater than 14D is recommended. Except for the solidified depths of 2D and 18D, the lateral resistances of the other model piles first increase and then decrease with increasing depth. The maximum values were located at the continuously solidified part and were obviously larger than those of the other pile sections. The maximum pile lateral frictional resistance was provided at the maximum depth of the continuously solidified part. After setting up the continuously solidified part, none of the bearing capacity of the pile ends exceeded 5%. The bearing capacity of the SCS group pile foundation was mainly shared by the continuously solidified part and the pile lateral frictional resistance. For the same pile spacing, the high strain damage zone of the soil at the bottom of the continuously solidified 2D–14D foundation was “abacus bead”; when the burial depth of the continuously solidified part reached 18D, the foundation soil exhibited “inverted bowl” damage.

Experimental Study on Bearing Behavior and Soil Squeezing of Jacked Pile in Stiff Clay

In order to study the bearing behavior and soil-squeezing of jacked piles in stiff clay, two groups of pile penetration tests were performed, with a rough pile that can reproduce the quick-shear behavior of the pile–soil interface, i.e., group 1 in stiffer clay, and group 2 in softer clay for comparison. For each group, the adjacent pile was additionally penetrated at different pile spacings to study the soil-squeezing effect on an adjacent pile. The results show that the penetration resistance increased rapidly at the beginning and then increased at a lower rate. This is because the resistance at the pile end increased rapidly at the beginning and then kept stable with fluctuations, whereas the resistance at the pile side continually increased due to the increasing contact area. Therefore, the ratio of the resistance at the pile end to the total penetration resistance exhibited a softening behavior, which first increased to a peak and then gradually decreased. In addition, there was soil-squeezing stress and soil-squeezing displacement in the ground and adjacent piles due to pile penetration. In stiffer clay, the soil-squeezing stress was larger than that in softer clay due to the higher strength, whereas the soil-squeezing displacement was smaller than that in softer clay due to the low compressibility. In addition, the nonlinear equation form y = ae−bx can be employed to describe the effect of pile spacing on the vertical flotation, horizontal deviation, and pile strain of the adjacent pile.

A Study on the Load-Bearing Characteristics and Load Transfer Mechanism of Bag Grouting Pile in Soft Soil Areas

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.

Vertical compressive bearing performance and optimization design method of large-diameter manually-excavated rock-socketed cast-in-place piles

To study the vertical compressive bearing characteristics of large-diameter rock-socketed cast-in-place piles, eight manually-excavated rock-socketed cast-in-place piles were subjected to vertical compressive on-site load and pile stress tests. The test results showed that the load–displacement (Q-s) curves of the eight test piles were all slow-varying, and the settlement of the piles was less than 11 mm, which met the minimum engineering requirements. The unloading rebound rate was between 55 and 75%, and the elastic working properties of the piles were apparent. The pile axial force gradually decreased with depth, and the slope of the axial force distribution curve reached a minimum in the moderately weathered muddy siltstone layer while the pile side friction resistance reached its maximum value. Pile end friction increases with the increase of load. But the pile end resistance was inversely proportional to the single pile length-to-diameter (L/D) ratio and the depth of rock embedment for the pile. The percentage of pile side friction resistance under maximum load was 86%, indicating that these were characteristic friction piles. Based on the test results and the current Chinese code, the friction coefficient of the pile side soil layer η and the total resistance coefficient of the rock-socketed section ζ were introduced. A revision to the calculation equation for the vertical bearing capacity of the rock-socketed cast-in-place pile in the code was proposed, together with an optimization design method for large-diameter rock-socketed cast-in-place piles.

Theoretical model for investigating three-dimensional effect in integrity test of open-end pipe piles

An innovative theoretical model of non-axisymmetric vibration of pipe pile (NVPP) is proposed in this paper to investigate the three-dimensional effect in the pile integrity test (PIT) for open-end pipe piles. A new dynamic equilibrium equation of the pipe pile is established based on the stress simplification assumption. It overcomes the inaccuracies of existing three-dimensional models in predicting the longitudinal wave velocity of pile material. The surrounding soil and soil plug conform to the classical plane strain assumption, while the pile end soil is simulated by the fictitious soil annular pile developed from the traditional fictitious soil pile. Theoretical solutions for the velocity response of each point on the pipe pile top are deduced and validated against existing solutions and FEM results. The NVPP model is then applied to analyze the characteristics of testing signals of PITs for thick-wall and thin-wall pipe piles. Problems concerned in actual PITs for pipe piles are settled and practical recommendations for acquiring high-quality testing signals with minimal interference are provided.

Pullout Bearing Capacity of End-Bearing Torpedo Anchors in Cohesive Soil Seabed

As a new type of deep-sea anchoring foundation, thetorpedo anchor has the characteristics of simple installation, low cost, and high bearing capacity. Compared with the torpedo anchor without an anchor wing, the end-bearing torpedo anchor forms pile end resistance using a bearing plate, thus further improving its uplift bearing capacity. By conducting the pullout model test of torpedo anchors, we have compared and analyzed the effects of the pullout angle and bearing-plate radius on the bearing characteristics of T, EN3, EN4, and EC types of torpedo anchors. Based on the model test results, we established the V-H envelope of torpedo-anchor bearing capacity using the regression analysis method. The results show that when the displacement is small, the load-displacement curve of the torpedo anchor increases in an approximately linear mode, and the curve fluctuates and gradually entersa stable state with the gradual increase of the displacement. With the increasing pullout angle, the bearing capacity of the torpedo anchor increases first and then decreases. When the pullout angle is 45°, the torpedo anchor has the maximum bearing capacity. When the pullout angle is constant, the order of bearing capacity generated by different types of torpedo anchors is as follows: EC > EN4 > EN3 > T, and the bearing capacity rises with the increasing bearing-plate area. Through regression analysis, it is concluded that for the torpedo anchors of T, EN3, EN4, and EC types, the V-H envelope of bearing capacity shows an outward convex trend, and the determination coefficient reaches 0.930, indicating that the established V-H envelope is suitable for predicting the bearing capacity of torpedo anchors.

Approach for a floating pile embedded in poroelasitc soil under horizontal dynamic load

The deformation mechanism in the horizontal direction of a floating pile under dynamic load should be paid extensive attention. The closed-form solution of dynamic characteristics of a floating pile in poroelasitc soil subject to horizontal dynamic load is obtained by a newly developed framework in this paper. Firstly, based on the three-dimensional continuum model and Biot’s poroelastic theory, the governing equations of the pile surrounding soil and pile end soil are respectively established. Secondly, the pile shaft reaction is calculated by use of the conventional method used in many existing literatures, and the pile base resistance is obtained with the aid of the Hankel transform technique and mixed boundary-value conditions that came from the contact interaction between a rigid massless disk with its beneath soil layer of finite thickness. Thirdly, the Timoshenko beam theory is applied to depict the pile vibration considering its shear deformation, and thus the dynamic impedance functions at pile head are derived. Subsequently, the correctness of the proposed solution is verified through comparisons with the existing results from other scholars. Finally, a parameter analysis about the thickness of the pile end soil, pile slenderness ratio and soil permeability are performed. Results suggest that the soil layer thickness and pile slenderness ratio have a pronounced effect on the pile dynamic behavior, and considering the soil permeability is more realistic to pile vibration response. The obtained results can exert great significance to the serviceability of floating pile for engineering practice.

Nonlinear analysis of horizontal bearing capacity of large-diameter rigid piles based on double conical strain wedge model

Large-diameter rigid piles are commonly employed in offshore wind turbine installations. A double conical strain wedge (DCSW) model is proposed in this paper to simulate the large-diameter rigid pile-soil interaction and determine the lateral subgrade reaction. A nonlinear analysis method is developed to predict horizontal response for large-diameter rigid piles installed in layered cohesionless soil, which can account for the effect of vertical side shear stress, pile end bending moment, and shear force. The rationality of the DCSW model is then verified by comparing its predictions with the experimental and theoretical results of existing studies. Subsequently, the new DCSW method is applied to investigate the horizontal bearing characteristics of the large-diameter rigid piles. The results reveal the presence of a rotation point situated at a depth range of (0.66–0.76) Lb (Lb is the burial depth of the pile). Additionally, the resisting bending moment caused by the vertical side shear stress between the pile-soil interface is able to enhance the horizontal bearing capacity of the pile.

Analytical Solution of Horizontal Dynamic Response of a Floating Pile Embedded in an Elastic–Poroelasitc-Layered Soil

The horizontal dynamic interaction problems of a floating pile with soil have received little attention from scholars in recent years. This paper first proposed an analytical solution for the dynamic characteristics of the floating pile subjected to horizontal steady-state excitation embedded in soil containing the groundwater table level. Based on Biot’s elastodynamic theory, the governing equations of the soil around the pile are obtained. By virtue of the Hankel transform technique and variable separation method, the shaft reactions and base resistances transferred from the soil are calculated and substituted into the dynamic equation of the floating pile derived by the Euler beam model. The dynamic impedance coefficient of the pile head in the frequency domain is obtained by using the transfer matrix method. Comparisons with the previous studies are performed to validate the accuracy of the presented approach. The effects of the thickness of the pile end soil, the slenderness ratio of the pile, the groundwater table level and the relative modulus of pile material on the pile dynamic response are investigated through several numerical analyses. The results show that there is an “active soil thickness” for the horizontal dynamic forced floating piles due to the reflection and refraction of the stand waves. Meanwhile, the effect of the groundwater table level should not be neglected to ensure the safety of pile foundation under service life.

Sensitivity analysis of influencing factors of pile foundation stability based on field experiment

Based on the finite element analysis software ABAQUS, this paper establishes a three-dimensional finite element simulation model. According to the measured data of a project in Qingdao, the settlement obtained by static load test is selected as the index to measure the stability of the pile foundation. The Poisson ratio, elastic modulus, angle of internal friction, and friction coefficient of the pile-soil contact surface of each layer of soil are selected as the factors affecting the stability of the pile foundation. The experimental results of settlement at all levels are analyzed and compared through the variable control and orthogonal experiment. Finally, the main factors affecting the stability of the pile foundation are determined as follows: the elastic modulus, Poisson ratio, friction coefficient, angle of internal friction of pile end soil, and the elastic modulus of the fourth layer of soil, which provides a specific reference value for the subsequent research on the stability of pile foundation.

Laboratory Test Study on Pile Jacking Penetration Mechanism Considering Different Diameter and Length Based on Photoelectric Integration Technology

Model tests are carried out on the jacked single piles of different diameters and pile lengths under the model pile of different diameters and pile lengths in clayey soil, which aims to investigate the penetration mechanical mechanism. How to accurately test the pile end resistance and pile side resistance during jacked pile sinking is particularly important. In this paper, a full-section spoke-type pressure sensor, a double diaphragm temperature self-compensating fiber Bragg grating (FBG) earth pressure sensor and a sensitized miniature FBG strain sensor are jointly applied to a single pile penetration model test to test a single pile driving force, pile end resistance and pile body stress during penetration. The test results show that the load transfer performance of test piles will be affected by different diameters, and the axial force transfer capability of a large diameter in the depth direction is better than that of a small diameter since the compacting effect is more obvious. The unit skin friction of the pile increases gradually as the depth increases, which is larger due to the lateral extrusion force increasing as the diameter increases. At the same depth, the unit skin friction of two different diameter piles demonstrates “friction fatigue”, which also decreases obviously as the depth increases. Under the conditions of this test, the maximum frictional resistance of the pile TP1 pile side is about 27.7% higher than that of the test pile TP2. In the static pile sinking process of three test piles in cohesive soil, 50% is end bearing; therefore, there is 50% friction, and the diameter influences the end bearing and the length influences the friction.

Load-Bearing Characteristics of PHC Piles Constructed by the Inner Digging Method Based on Ultimate Load Testing and Numerical Simulation

This paper studies the load-bearing characteristics of two prestressed high-strength concrete (PHC) pipe piles constructed by the medium mid-digging and hammering methods. The ultimate load tests and numerical simulations of the pipe piles constructed by both methods were carried out to analyze the ultimate lateral resistance, and ultimate resistance performance characteristics of the two pipe piles and the influence of the wall thickness of the pipe piles on the bearing performance. The test results show that the pipe pile constructed by the middle inner digging method has a higher pile quality. The single pile bearing capacity of the pipe pile constructed by the middle inner digging method is 50% higher than that of the common hammering method. The enlarged part of the pile end has an obvious effect on improving the bearing capacity. The settlement of the pipe pile constructed by the middle inner digging method is smaller than that of the hammering method. The large diameter pipe pile constructed by the middle inner digging method usually shows characteristics of the end-bearing pile. The resistance of the pile end accounts for 40–50% of the top load. The numerical simulation results agree with the field test and are compared and discussed. The simulation results show that when the bearing capacity of the pile is provided by the pile side frictional resistance, the influence of the pile wall thickness on the bearing capacity is insignificant. When the top pile load is close to the bearing capacity of the pipe pile, the influence of the pipe pile wall thickness on the bearing capacity is greater.

Research on the Bearing Capacity and Sustainable Construction of a Vacuum Drainage Pipe Pile

The vacuum drainage pipe (VDP) pile is a new type of pipe pile on which the current research is mainly focused on laboratory tests. There is little research on bearing characteristics and carbon emissions in practical engineering. To further explore the bearing capacity and sustainable construction of vacuum drainage pipe piles, static load tests were conducted to investigate the single-pile bearing capacity of ordinary pipe piles and vacuum drainage pipe piles, as well as soil settlement monitoring around the piles. Then, the Q-S curves of the two piles, the pile-side friction resistance under different pile top loads, and the development law of pile end resistance were compared and analyzed. Finally, based on the guidelines of the IPCC, the energy-saving and emission-reduction effects of VDP piles in practical engineering were estimated. The results indicate that, after vacuum consolidation, the VDP pile basically eliminates the phenomenon of soil compaction and does not cause excessive relative displacement of the pile and soil. VDP piles have increased lateral friction resistance, and compared to traditional piles, their ultimate bearing capacity is increased by 17.6%. Compared with traditional methods, the VDP pile method can reduce carbon emissions by 31.4%. This study provides guidance for the production and design of future VDP piles and demonstrates the potential of VDP piles for energy conservation and emission reduction in comparison to traditional methods.

The Influence Depth of Pile Base Resistance in Sand-Layered Clay

Pile base resistance is an important part of the ultimate bearing capacity, and the soil within a certain range above and below the pile end contributes to the pile base resistance. In general, pile base resistance is calculated according to the average value of soil strength within a certain range of the pile end in the current calculating method, so it is very important to determine the influence range of pile base resistance. Based on the soil parameters and the results of the cone penetration test of the LiuHua 11-1 site in the South China Sea, the difference of pile base resistance calculated by different methods, the regularity of pile base resistance affected by calculation depth range is revealed. Additionally, the numerical simulation method is used to analyze the distribution of a plastic zone around the pile end in homogeneous soil and stratified soil, the results show the influence depth range of pile base resistance is 0.12 D above the pile end to 0.83 D below the pile end in clay, and the influence depth range is 0.9 D above the pile end to 1.3 D below the pile end in stratified soil.

The axial behaviour of piles driven in chalk

This paper describes research into the poorly understood axial behaviour of piles driven in chalk. Comprehensive dynamic and monotonic axial testing on 27, mostly instrumented, piles undertaken for the ALPACA joint industry projects is reported and interpreted covering: diameters between 139 mm and 1·8 m; lengths from 3 to 18 m; different pile material types; tip and groundwater conditions; and ages after driving. The experiments show the factors that influence resistance most strongly are: (a) pile end conditions; (b) slenderness ratio and flexibility; (c) shaft material; (d) age after driving; (e) relative water table depth; and (f) whether loading is compressive or tensile. Varying the factors systematically identified a remarkable average long-term shaft resistance range from below 11 kPa to more than 200 kPa for piles driven at the same low- to medium-density chalk test site in Kent (UK). Dynamic and static analyses demonstrate that soil resistances to driving were generally well predicted by the Chalk ICP-18 short-term formulation. Considering the piles’ long-term behaviour, the Chalk ICP-18 approach over-predicted capacity, while the widely used CIRIA approach proved over-conservative for most cases. The research enabled the development of a revised ‘ALPACA-SNW’ long-term capacity assessment method that matches the test outcomes far more faithfully.

Experimental study of the thermodynamic properties of high thermal conductivity energy pile

In this paper, high thermal conductivity concrete (containing 4% graphite and 0.6% steel fiber) was prepared as a pile material by a model test. A high thermal conductivity energy pile was produced. The temperature field distribution of the pile and soil, the additional stress of the pile, the soil pressure at the pile end, and the displacement of the pile top were analyzed. The results showed that compared with the thermal conductivity, compressive strength, and flexural strength of ordinary C30 concrete, those of the high thermal conductivity concrete were increased by 30%, 11%, and 9%, respectively. Under load, the additional stress of the pile was large in the middle and small at both ends. After three thermal cycles, the maximum additional tensile and compressive stresses of the pile were 0.48 MPa and −0.58 MPa, respectively. The maximum value of the soil pressure at the pile end decreased with an increase in the number of thermal cycles. Thermal cycles caused cumulative pile top settlement, with a final settlement of 0.26 mm. In practical engineering, the influence of long-term thermal cycles on the safety of buildings should be noted.

Field Test Study on the Bearing Capacity of Extra-Long PHC Pipe Piles under Dynamic and Static Loads

Pretensioned prestressed high strength concrete (PHC) pipe piles are widely used in various engineering foundations, which have the advantages of high single pile bearing capacity, strong adaptability to geological conditions and high degree of construction mechanization. In order to study the vertical compressive bearing performance and settlement characteristics of ultra-long PHC pipe piles, high strain dynamic detections and static load tests were carried out on four PHC piles with a diameter of 0.9 m on site. It can be seen from the field test that the bearing capacity of the prefabricated pipe piles was time-dependent. By the end of the dynamic test, the bearing capacity of each test pile increased by 27% to 66%. The static load test also verified the rationality of the value of the restitution coefficient. Therefore, the final bearing capacity of the pile foundation can be predicted by using the high strain initial driving results and the restitution coefficient, which can reduce the repeated driving process, effectively save the cost and improve the engineering efficiency. Under 2.1 times the design load, the change range of the pile concrete modulus is from 37.5 GPa to 52 GPa, the change range of the pile side friction resistance is from 0 kPa to 97 kPa and the change range of the pile end to pile bottom load ratio is from 0% to 7.54%. During the test, the shaft friction and end bearing of the lower part of the piles were not fully mobilized. The shaft friction resistance, the end resistance and the movement behavior of the pile top and the end of the piles can provide parameter references for the subsequent design and construction of the piles.

Field testing study on jacked pile penetration characteristics in laminated clay based on FBG sensing technology

In order to analyze the change of static pressure pile characteristics in silt and silty clay with the penetration depth, two PHC pipe piles were penetrated in the field in the actual project, and the research was based on the full section test technology and FBG test technology. The results show that the pile pressure increases with the increase of the pile penetration depth; The change of pile tip resistance is affected by the soil layer hardness; When the pile tip is in the transition stage, the pile tip resistance increases significantly; In the process of pile penetration, the hardness and brittleness of the soil layer will be affected by the pile penetration, and the different soil layers will have different effects on the pile tip resistance of the two piles; When the pile goes deep into the soil, the pile side resistance will change slowly, but it will usually increase. This fluctuation is related to the difference of the soft and hard layers of the soil layer, and will also be subject to performance constraints; The pile end resistance ratio in hard soil will be smaller than that in soft soil, which will further affect the load sharing ratio of the test pile. The test results can provide support for practical engineering technology.

Analysis of Settlement of Group Pile Foundation in Linear Viscoelastic Soil

The settlement of a group pile foundation is the result of elastic-plastic settlement of the pile and rheological settlement of the soil. Unfortunately, most research only considers elasto-plasticity settlement of piles or rheological settlement of soils. Classical theories like the Poynting-Thompson model only provide some prediction for the elasto-plasticity behavior of pile groups, which cannot satisfactorily reflect the total settlement characteristics of pile group foundation. In the current paper, we presented a method to study settlement behaviors of pile group foundation in linear viscoelastic soil based on the pile-pile interaction factors, the calculated equation of settlement of single piles and pile groups under vertical loads that are derived, the influence law of pile end resistance, pile spacing, slenderness ratio, elastic modulus ratio, and Poisson ratio on pile end load ratio, and the interaction factors that have been presented. Finally, some typical predictive examples have been presented for a 2 × 2, 3 × 3 group pile showing settlement from a field test. It is found that the pile-pile interaction factors increase with the increase of the pile-soil elastic modulus ratio and length-to-diameter ratio but decrease with the increase of the ratio of distance to diameter, and the ratio of distance to diameter has little effect on the interaction factor when pile spacing is more than 10 d (d is the diameter of the pile). The error between the field test results and computed data is 14.9%, the settlement calculated by the present method shows good agreement with the reported results, and the correlativity coefficients R2 are greater than 0.9223, which signifies that the present method is suitable for the theoretical calculation and prediction of the composite foundation settlement of linear viscoelastic soil when piles are used to strengthen the foundation. The method would provide a unique view to quantitative prediction of the settlement characteristic of group pile foundation.