Bottom Of Pile Research Articles

Improved calculation of the rigidity of double-row piles and double-beam composite support and displacement analysis under different soil properties

As a new type of cantilever-type supporting structure, the double-row pile supporting combination system can improve the overall rigidity to maintain the safety and stability of the side of the foundation pit. The case of a double-row pile foundation pit support project in the Wanquan District of Zhangjiakou is taken as an example. Based on the existing double-row pile crown beam stiffness coefficient calculation method, the effect coefficient of the crown beam and the coupling beam is introduced to optimize and improve the effect of the coupling beam and the crown beam. The results show that (1) in the calculation of the double-row pile structure, the common lateral restraint effect of the crown beam and the connecting beam on the double-row supporting piles should be considered, and the rigid connection of the crown beam and the connecting beam should be taken as a whole to improve the rigidity coefficient of the double beam lateral support of a rectangular double-row pile. (2) The combined stiffness of the double-beam combined support system has a greater impact on the displacement of the pile top, and the displacement under a combined stiffness of 40-50 MN/m are close to the observed value. The calculated length of the crown beam and the introduced crown beam and connecting beam effect coefficient have a great influence on the combined stiffness of the double-beam composite support system. The combined stiffness decreases with the increase of the calculated length, and increases with the decrease of the effect coefficient. (3) The lateral support stiffness of the double-row piles under the double-beam composite support system is affected by the difference between the vertical and lateral displacements of the front and rear piles. The maximum lateral displacement of the front and rear piles is affected by the friction angle of the soil, the cohesion and the proportional coefficient of the horizontal resistance of the soil. Changing the tensile strength will not affect the displacement and deformation of the double-row piles. There is a displacement inflection point below the buried depth of the foundation pit and within the scope of the pile bottom. The displacement at the inflection point is equal under different friction angles and different cohesive forces.

Research on detection technology of squeezed branch and disk pile under boulder geological condition

The detection methods of the cavity and cavity size and pile quality of squeezed branch and disk pile are not perfect. Based on the 65 pier of a viaduct in Zhongshan City, this paper uses caliper, cross hole acoustic wave method, core pulling method and tube wave method to detect the squeezed branch and disk pile, and compares and analyzes the advantages and disadvantages, applicable conditions and detection results of each method. It can be seen from the test results that both caliper and cross hole acoustic wave method can detect the length of squeezed branch pile, while core pulling method and tube wave method can detect the quality of pile body and the thickness of sediment at the bottom of pile. The test results are basically consistent and verified with each other, and the specific data such as the length of branch and the thickness of sediment are slightly different. In this paper, caliper, cross hole acoustic method, core pulling method and tube wave method are verified and analyzed to provide ideas and support for the later detection of squeezed branch and disk pile.

Research horizontally loaded pyramidal piles with compacted bottom and their calculation

The results of experimental and theoretical research in work features of a rammed pyramidal pile with compacted bottom for horizontal load in clayey soils are presented. The experimental cast-in situ pyramidal piles with compacted bottom were made at 2 experimental sites, composed of clayey soils. Static horizontal load tests were carried out. At each stage of loading, horizontal displacements were measured at the load application level and at a height of one meter from the top edge of the pile. The “horizontal load - pile head displacement” dependencies were obtained. It was found that the rotation of the pile in the soil occurs without bending, i.e. according to a rigid scheme, and also that compacted bottom prevents horizontal displacement of the pile bottom. Based on the analysis of the results of static tests of piles, a design scheme has been created, in which the pile is considered as a rigid rod buried in a multilayer linearly deformable base with a point of zero displacements at the lower end of the pile. In accordance with the design scheme, an analytical method for calculating a pyramidal pile with compacted bottom for horizontal load and bending moment has been developed. The calculation method allows to determine the horizontal displacement of the pile head in any section along the depth, the angle of rotation of the pile, bending moment and shear force along the length of the pile.

3D Roughness Measurement of Failure Surface in CFA Pile Samples Using Three-Dimensional Laser Scanning

The bearing capacity of CFA (Continuous Flight Auger) pile is not able to reach the design capacity if proper construction is not performed due to the soil collapse at the bottom of the pile. In this paper, three pile samples were prepared to simulate the bottom of the CFA pile: grouting sample; mixture of grouting and gravel; mixture of grouting and sand. The failure surfaces of each sample obtained by a uniaxial compression tests were represented as a three-dimensional point cloud by three-dimensional laser scanning. Therefore, high resolution of point clouds can be obtained to simulate the failure surfaces of three samples. The three-dimensional point cloud of each failure surface was analyzed by a plane to points histogram (P2PH) method and a roughness detection method by kernel proposed in this paper. These methods can analyze the global roughness as well as the local roughness of the three pile samples in three dimensions. The roughness features of the grouting sample, the mixed sample of grouting and sand, and the mixed sample of grouting and gravel can be distinguished by the sections where points of each sample are predominantly distributed in the histogram of the proposed method.

The detailed particle breakage around the pile in coral sand

Detailed particle breakage adjacent to a pile has great influence on the settlement and bearing capacity of a pile foundation. Before the pile test, coral sand was divided into different grain-size groups and dyed in different colors, then mixed as the ground soil. After pile penetration, the sand around the pile was divided into many zones and sampled. Grains in different colors in each size range of each sample were discerned quantitatively. Results show that the settlement curve dropped fast and the skin friction of pile was small due to the obvious particle breakage. In each zone, the actual particle breakage in each size range was different from the change in relative mass percentage, and the lost of angular edges is the dominant type of particle breakage under the bottom pressure of pile. The index Bag, excluding the interference effect of size overlap between fragments and unbroken grains in each size range, was slightly larger than Bg for most zones around the pile. The breakage-zone was limited to 1.5 times of the pile diameter at the radial direction and 2.5 times at the depth direction, which is much deeper than that in silica sand. Particle breakage at some distance from pile bottom is larger than that at the very bottom of the pile due to the shearing effect in the sand. Detailed particle breakage around the pile is useful in studying the interaction between the pile and crushable granular soil.

Calculation Method for the Critical Thickness of a Karst Cave Roof at the Bottom of a Socketed Pile

The thickness of a karst cave roof at the bottom of a socketed pile plays an important role in the vertical bearing capacity of the socketed pile in the karst region. In practice, its thickness is simply recommended to be not less than 3 times the diameter of the socketed pile, regardless of the geological conditions and the size of the cave itself. In this study, we present an approach for calculating the critical thickness‐to‐diameter ratio of a karst cave roof η (η = h/d, the ratio of karst cave roof thickness to pile diameter) based on the generalized Hoek–Brown criterion by virtue of the limit analysis method, which considers the pile tip load, hardness degree of the intact rock, and rock mass quality. The analysis results show that less load at the bottom of the pile, higher quality of rock mass, and more hard rock all lead to a smaller critical thickness‐diameter ratio, whereas the critical thickness‐to‐diameter ratio is greater. The validity of the proposed method is verified through a physical model test.

Thermal Stability Evaluation Method Based on Pile’s Bearing Capacity in a Permafrost Region

Pile foundations are widely adopted in the Qinghai–Tibet Railway. The pile’s bearing capacity must be influenced the trends of global warming, rising foundation soil temperatures, expanding active layers, ground ice melting, etc. Thus, the pile’s long-term bearing capacity must be understood, and methods for evaluating its stability in permafrost regions must be developed. The bearing capacity of a pile foundation in a permafrost region is caused by the freezing strength of the pile–soil interface and support force at the pile bottom. Based on the formation mechanism of the bearing capacity of pile foundations in permafrost regions, the stability ratio of the freezing area and the freezing strength between the pile and soil are proposed to evaluate the thermal stability of the pile’s bearing capacity in permafrost. Using the method, a bearing capacity study on a single pile in typical moist permafrost and two piles in a permafrost region where warm groundwater is underground is performed. Compared with the field-measured value, the evaluation method proves to be correct and effective. Using the two parameters dependent on the soil–pile interface temperature, the effect of the thermal stability of pile bearing capacity may be described intuitively. Thus, both parameters are conducive to the analysis of pile bearing capacity formation mechanism in permafrost.

Influence of Karst Caves at Pile Side on the Bearing Capacity of Super-Long Pile Foundation

The differences in development and situation of karst caves lead to two kinds of karst caves, and the karst cave may be on the pile side or at the pile bottom, which has a different influence on the bearing capacity of pile foundation. The paper presents a numerical analysis of the influence of karst caves at pile side on the bearing capacity of super-long pile foundation in karst areas. According to the size of pile foundation of a real bridge project, this paper modelized karst caves and investigated the karst cave from the effect of length, height, and thickness of roof on horizontal and vertical bearing capacity of pile foundation. The main conclusions can be drawn as: when the horizontal displacement at the top of pile foundation is greater than 0.05 m, the horizontal load is correlated positively with the length of karst cave; when the vertical displacement is greater than 0.07 m, the vertical load is correlated negatively with the thickness of the roof of karst cave. However, the height of karst cave has little effect on the bearing capacity; also the existence of karst cave has little influence on the dynamic response of pile foundation. The results of this study can be important with reference to the design and construction of pile foundations in karst areas.

Study on Model and Tests of Sheet Pile Wall with a Relieving Platform

A new type of retaining wall, the sheet pile wall with a relieving platform, is introduced in this paper. Based on the prototype retaining wall with a height of 12 meters, the model tests with a geometric similarity ratio of 7 are designed and we focus on the model production and analysis on the test results. Some comparative analyses between the measured values and the calculation values by using the theoretical calculation method and finite difference method are carried out, including Earth pressure behind the wall, prepile resistance force, the bending moment, and the deformation of rib pillars in the retaining wall. The results show that Earth pressure behind the wall has a linear increase with the depth and lies between Rankine Earth pressure and Earth pressure at rest. Moreover, the prepile resistance force can be approximated by the m method, and the bending moment can be also used for approximate calculation by the m method and is larger than the results calculated by the finite difference method. It is also observed that there is a zero‐displacement point on the pile bottom, and the Earth pressure above the point behind the pile develops from Earth pressure at rest to the active Earth pressure; the Earth pressure under the point behind the pile develops from Earth pressure at rest to the passive Earth pressure. Therefore, the Earth pressure behind the bottom wall is larger than the calculated value by the Rankine theory. Finally, the displacement of the rib pillars is greater than the calculated results using the finite difference method and exceeds the standard requirements, owing to the failure of the retaining wall, and the unloading board needs to be constructed to improve the retaining wall’s behaviour. These findings verify the model’s credibility and provide an underpinning for studying the behavior of the retaining wall.

Side Friction of Rock‐Socketed Piles Involving Thick Sediment

This paper investigates the skin friction transfer characteristics of the rock‐socketed section of a rock‐socketed pile resting on thick sediment by conducting in situ core‐drilling tests and static loading tests. Test results show that when using the impact hole‐forming method in weakly cemented soil, a layer of sediment is deposited at the pile bottom. Due to the existence of sediment, when the load reaches a certain value, sudden and large subsidence is observed. This indicates that the end resistance does not contribute to the bearing capacity. Thus, it is not appropriate to consider both end resistance and side resistance in the existing design method of a rock‐socketed pile. The bearing capacity of a single rock‐socketed pile should be determined according to the side resistance of the soil layer and rock‐socketed section only. Numerical analysis is performed to determine the deformation and load‐carrying capacity of the pile and the distribution of friction on the sides of the rock‐socketed segment. Under a given applied load, small settlement is observed when socketed thickness and rock strength are relatively large. The distribution of side friction of the socketed segment along the vertical direction shows a double‐peak saddle shape. When the socketed thickness and rock strength are relatively smaller, the lower peak is higher than the upper peak, and conversely, when the socketed thickness and rock strength are relatively larger, the lower peak is smaller than the upper peak. For a given applied load on the pile top, smaller socketed thickness results in larger settlement and side friction. Due to the thick layer of sediment, the axial force of the rock‐socketed segment of the pile gradually decreases along the vertical direction from the applied load on the pile top to zero at the bottom. According to the mechanical properties at different shear stages, a function is derived for the complete constitutive model for a pile‐rock interface. Analytical solutions for the friction of a single pile are obtained under the conditions of failure and elasticity deformation of the surrounding rock. Its load transfer equation is derived as well. Accordingly, an equation is proposed for calculating the bearing capacity of rock‐socketed piles resting on sediment at the bottom.

The long piles interaction with the surrounding and underlying soils, taking into account the linear and nonlinear rheological properties

The article presents the long incompressible pile with a two-layer base interaction problem formulation and solution, taking into account the underlying soil visco-plastic properties by the analytical method. A significant change in the stress-strain state at the base of an incompressible pile when stress changes around the pile side surface is shown. It is shown that in such conditions, the stress under the pile bottom varies significantly over time, which can lead to the pile bearing capacity loss in the long run.

Experimental study on deformation characteristics of collapsible loess under isotropic stress

In order to study the deformation characteristics of collapsible loess and to construct different vertical stresses, different isotropic stresses are used to represent the vertical stresses, and their corresponding stresses are set to be the hidden stresses in different positions of collapsible loess foundation are analyzed by using 0, 50, 100, 220, 330 and 400 kPa. In this study, various kinds of deformation analysis of collapsible loess are needed. Ground settlement tester, GJY K0 tester produced by Suzhou Longstan Automation Factory and ADINA software are used. Experiments show that different isotropic stresses are applied to the foundation, and the hidden stresses of the loess are gradually decreasing under the action of different filling heights. At the same time, the higher the height of the fill, the faster the decline of the underlying stress of the foundation loess. With the increase of time at the bottom of the cushion, the corresponding underlying stress at the midline decreases, while with the increase of the height of the fill, the corresponding underlying stress at the midline rises. Study of the underlying stress at the bottom of the pile is set up differently. Under certain time and position of the pile bottom, increasing the isotropic stress can increase the hidden stress at the corresponding pile bottom, and change the filling height at the pile bottom has little effect on the hidden stress at the pile bottom. Under the combined action of water content and isotropic stress, they are positively correlated with the change of lateral stress. With the increase of isotropic stress, the K0 coefficient rises as a whole. This study can provide a strong reference for the deformation characteristics of collapsible loess itself, and help construction workers to improve the safety of the project in the field of engineering construction.

Study of Shaking Table Test of Rigid-subrigid Pile Composite Foundation under Sandy Field Condition

To study the seismic response of rigid-subrigid pile composite foundation, shaking table test was conducted under sandy field condition. The experimental results show that the acceleration response strength of the pile top is greater than that of the pile bottom, and is smaller with the increase of buried depth; seismic wave types will have an impact on the acceleration amplification effect; from pile bottom to pile top, the peak value of Fourier spectrum increases gradually, and the frequency distribution of Fourier spectrum in frequency domain does not change. The frequency range of the peak value of Fourier spectrum under three kinds of seismic waves is different; with the peak acceleration of the input excitation increase, the strain peak of pile body changes more and more significantly along the length direction, and the strain peak of rigid pile appears abnormal, which is the weak part of seismic resistance.

Stress State of Conical Granular Pile

The authors analyze the effect revealed at the Institute of Mining, SB RAS in the 1970s. This effect consists in a noticeable off-center displacement of the maximum normal pressure on the bottom of a conical pile when heaped. The new experimental data are presented. The stress-stress analysis of the pile between two parallel smooth plates is solved using a 3D discrete element method. The calculations prove the indicated effect.

Reinforcement Effects of Isolation Piles on the Adjacent Existing Tunnel in Building Construction

Similar material model test and numerical simulation method were used to study the reinforcement effect of isolation piles on the existing shield tunnel structure in the adjacent building construction for analyzing foundation pit excavation and new building construction approaching existing shield tunnel engineering. The numerical simulation orthogonal experiment was used to optimize four isolation pile parameters. The conclusions were obtained as follows: (1) Isolation piles could share horizontal load of the soil at the rear side of the support structure and reduce horizontal displacement of the soil. As a result, maximum horizontal displacement of the tunnel structure and differences in horizontal displacement between the tunnel structure roof and the floor after foundation pit excavation and building loading were decreased. The horizontal displacement and torsional deformation of the tunnel structure toward the direction of the foundation pit were controlled, and the increase in internal forces of the transverse tunnel structure was also restrained. (2) At the elevation above the tunnel roof, the increase in burial depth of the isolation pile top slightly affected the reinforcement effect on the tunnel structure. The increase in burial depth of the isolation pile bottom could improve the reinforcement effect. Thus, burial depth of the isolation pile bottom should be properly increased in the engineering practice. The reduction in pile spacing could improve the reinforcement effect. Accordingly, pile spacing should be properly selected in the engineering practice. With the increase of diameter of the isolation pile, the reinforcement effect of isolation piles increased obviously. (3) Pile diameter had the greatest influence on the reinforcement effect of isolation piles, followed by burial depth of the pile bottom, pile spacing, and burial depth of the pile top. Orthogonal experiments indicated the following optimal parameter values: a pile diameter of 1.2 m, a burial depth of the pile bottom of 2H, a pile spacing of 1.6 m, and a burial depth of the pile top of 0.75Z.

Powder-spreading mechanisms in powder-bed-based additive manufacturing: Experiments and computational modeling

The packing density of the powder layer plays a key role in the final quality of the parts fabricated via powder-bed-based (PBB) additive manufacturing. This paper presents a combined experimental and computational modeling study on the scraping type of powder-spreading process, in order to understand the fundamental mechanisms of the packing of the powder layer. The deposition mechanisms at the particulate scale, including particle contact stress and particle velocity, are investigated, using the discrete element method, while the macro-scale packing density is validated by experiments. It is found that there is a stress-dip at the bottom of powder pile scraped by the rake. This stress-dip makes the powder particles uniformly deposited. Three kinds of deposition mechanisms dominating the powder-spreading process are identified: cohesion effect, wall effect, and percolation effect. The cohesion effect, which leads to particle agglomerations and thus reduces the packing density, becomes stronger with the decrease of particle size. The wall effect, which leads to more vacancies in the powder layer, becomes stronger with the decrease of layer thickness or the increase of particle size. The percolation effect exists in bimodal powder particles, which leads to particle segregation within the powder layer and thus reduces the packing density. The three kinds of deposition mechanisms compete with each other during the powder-spreading process and make combined effects on the packing density of the powder layer.

Applications of Morison's equation to circular cylinders of varying cross-sections and truncated forms

Abstract Morison's equation is used for formulating forces and moments due to waves acting on circular cylinders of varying cross-sections and truncated forms. First, the usual case of bottom-mounted constant-diameter circular piles extending from seabed to free surface is revisited and then forces and moments for the truncated form are formulated. Further, linearly and parabolically varying diameter cases are considered for both bottom-mounted and truncated cylinders. The formulations are derived using linear wave theory; however, by adopting a heuristic nonlinear approach integrals are evaluated from pile bottom to wave crest instead of still water level. Corresponding linear formulations are obtained as special cases by simply setting the non-dimensional nonlinearity parameters to zero. Thus, for each cylinder configuration two different force and moment formulas are presented by integrating to actual free surface and to still water level. All the results are arranged in forms which are practically easy to use. Finally, analytical expressions for determining maximum total force and moment values are given and sample calculations are presented for all configuration types.

Absolute timing of Caledonian orogenic wedge assembly, Central Sweden, constrained by Rb–Sr multi-mineral isochron data

Multi-mineral Rb–Sr isochron ages for mylonites of the Caledonian nappe pile (Jämtland, Sweden) constrain the orogenic evolution of the central Scandinavian Caledonides. An age of 437.8 ± 3.9 Ma from a metamorphic leucosome in the central nappe stack dates crystallization of migmatized gneiss. Thirteen isotopic ages derived from mylonites across all structural levels are between 434.6 ± 6.9 Ma and 426.3 ± 3.1 Ma. These results, complemented by a dense network of kinematic field data, are interpreted to reflect the timing of protracted top-to-the-ESE general shear under decreasing amphibolite- to upper-greenschist-facies conditions across all nappes. Three samples, derived from the top, middle and bottom of the nappe pile, yield additional deformation ages between 416.0 ± 3.6 Ma and 410.1 ± 3.0 Ma. These ages are interpreted to represent post-assembly imbrication of the nappe stack under decreasing metamorphic conditions. The new tectonochronologic data are consistent with a tectonic model that explains nappe stacking in Jämtland by three stages of ESE-directed in- and out-of-sequence thrusting. In the first stage, postdating earlier subduction–exhumation of the high-grade metamorphic Seve Nappe Complex, the latter was emplaced in-sequence in the lower/mid-crust above nappes in its footwall (foreland) at c. 430 Ma. This event is related to the collision of Baltica with an island arc. Concurrently at c. 430 Ma, determined by paleogeography and structurally unrelated to the first stage, second-stage out-of-sequence thrusting emplaced the Köli Nappe Complex atop the developing nappe stack during final Baltica–Laurentia collision. Eventually, imbrication and exhumation of the composite Jämtland nappe stack in the uppermost middle crust during the third stage at c. 414 Ma was caused by continuous underthrusting of Baltica beneath Laurentia. This three-stage thrust model reflects the complex interactions of Baltica–arc–Laurentia collisions that were accommodated by two merging subduction zones.

Double layer load cell test of self-balanced method for bearing capacity of super-long bored piles

The large diameter super-long bored pile’s bearing capacity is generally very high. The self-balanced method is a new type of static load test method, and it is suitable for the test. At Yueqing Bay No. 1 Bridge, a pile with diameter of 2500 mm and length of 112.0 m was discussed in detail. The post grouting technology at pile bottom was used. The self-balanced method was carried out before and after post grouting. The double layer load cell test method was introduced. The ultimate bearing capacity of the upper, the middle, and the lower part piles were obtained. The test results were converted to the traditional top-down method. The ultimate bearing capacity before grouting was 46932 kN, and it was 70680 kN after grouting. The increment percentage was 50.6%.

A novel measurement method of toe debris thickness for bored piles based on one-dimensional wave theory

The existence of toe debris at the bottom of the bored pile will reduce the bearing capacity of the pile. This paper develops a novel equipment to measure the thickness of toe debris for bored piles. The equipment consists of a test rod, test hammer, velocimeter, transmission cable and data receiving and processing device. Based on the one-dimensional wave theory, the mechanism of the sudden change of the velocity time curve received at the top of the test rod is analyzed, which is caused by the change of the wave impedance at the interface between the test rod and the sediment, thus the feasibility of the equipment is verified in theory. Finally, numerical simulations of toe debris under various working conditions are carried out to verify the reliability of the equipment. The results show that the test curves are sensitive to the materials of test rod using proposed equipment when the thickness of toe debris is equal or greater than 50 cm, and the test values are all larger than actual values, which meet the requirement of relevant specifications. The test results are more accuracy when the thickness of toe debris is less than 50 cm. when the excited force is large, not only the sudden change is easy to be discriminated, but also the test accuracy can be assured. The remainder toe debris meet the requirement of relevant specifications after clearing pile hole according the proposed method. And the device is not affected by the properties of the sediment material, which indicates that the proposed equipment can perform well to test the thickness of toe debris.