Unit Side Resistance Research Articles

Assessment of Axial Resistance of Piles Considering Consolidation Setup and Aging Setup Using Direct Pile Cone Penetration Test Methods

This paper focuses on evaluating the increase in axial pile resistance subjected to both consolidation and aging setups. Consolidation and aging setup models were first developed to estimate the setup parameters based on databases collected from literature, which include 10 instrumented piles for consolidation setup and 26 test piles for long-term aging. The eight top-performing pile cone penetration test (CPT) methods that were evaluated in a previous study were used to estimate the side resistance of soil layers at 14 days after pile driving. The developed consolidation and aging setup models were then used to extrapolate the results to evaluate the side resistance of each soil layer at the end of consolidation and for long-term aging. The estimated side and total resistances were compared with the measurements from pile load tests considering both consolidation and aging setups. The resistances estimated before and after completion of excess pore water pressure dissipation indicates that significant aging takes place after consolidation setup. The value of consolidation setup parameter ( Ac) was 0.53, and, for aging, the setup parameter ( Ag) was 0.23 in clay and 0.16 in sand. The results show that all pile CPT methods with/without using a consolidation setup model tend to underestimate the unit side resistance of clay soil layers. The use of pile CPT methods in combination with an aging model improved the accuracy of pile CPT methods, and this was verified using load test results for five piles subjected to aging. The Philipponnat and University of Florida (UF) methods showed the best performance on estimating the total resistance of piles subjected to aging.

Field Test Study on Vertical Bearing Characteristics of Coal Rock

Coal rock is rarely used as the foundation bearing strata. For buildings located on coal rock, it is a reasonable and feasible way to obtain the vertical bearing characteristics of coal rock through field tests. Three plate load tests and two bi-directional load tests were carried out, and the design parameters of the vertical bearing capacity of the shallow foundation and the deep foundation were obtained, respectively. The plate load test results show that the pressure–settlement curve of coal rock is a steep-drop-type, and the deformation modulus decreases with the increase of the pressure. The bi-directional load test results show that the unit tip resistance-displacement curve of coal rock is a steep-drop-type, and the load transfer function of the unit tip resistance is an ideal elastic–plastic curve, and the displacement value corresponding to the ultimate bearing capacity is about 1% of the pile diameter. The load transfer function of the unit side resistance of coal rock is a hyperbolic curve. The equivalent pile top load–settlement curve obtained according to the load transfer functions of the unit tip resistance and the unit side resistance is consistent with the equivalent conversion results of the bi-directional load test method.

A new method for extrapolating the load-displacement response of drilled shaft foundations for interpretation of side capacity

In this study, the side capacity of drilled shaft foundations is estimated from partially-mobilized load–displacement field data using a new method in the extrapolation of load–displacement response. A dataset of 138 bi-directional load tests is used to evaluate the degree of mobilization of unit side resistance. A total of 612 unit side-resistance curves obtained from measured strain gauge recordings are utilized in this study. The proposed extrapolation approach is based on a new technique, the Double Tangent method, characterizing the extent of mobilization for each unit side-resistance curve. Roughly, 12% of the dataset exhibits a fully-mobilized load–displacement response, with the remainder exhibiting varying degrees of a partially-mobilized response. Fully-mobilized records are further characterized using the Double Tangent method over different ranges of mobilization, resulting in four regression models based on predominant soil types. Each model is assessed statistically, and a global regression model is found suitable to predict maximum unit side resistance. The global model is further validated using two independent load test datasets, comparing measured values of unit side resistance against predicted values. The model is then used to predict maximum unit side resistance for all partially-mobilized data within the dataset, and the results are compared to two extrapolation techniques currently used in practice. The corresponding resistance-displacement response is extrapolated using a proposed asymptotic curve-fitting function for side resistance, and an example extrapolation is illustrated to showcase how the proposed method can be used in engineering practice.

An Experimental Study on Unit Side Resistance of Gaziantep Limestone

In this study, the correlation between the uniaxial compressive strength and unit side resistance of Gaziantep limestone was investigated experimentally for dry and fully saturated conditions. The results were compared with the methods given in the literature which correlate these two parameters. The linear correlations significantly overestimated the measured side resistance values for all tests while the non-linear methods generally overestimated the unit side resistance under fully saturated conditions but provided a reasonable estimation for dry samples. As a result, a linear correlation and non-linear correlation ranges for estimating the unit side resistance of such limestones were also suggested.

Analysis of Vertical Response of Drilled Pile at the Crest of Rock Slope Based on Shear Behavior

This paper proposed a method for analysis of a drilled pile under vertical load at the crest of rock slope. Based on wedge theory, a modified model of normal stiffness of socket wall affected by the slope is obtained. Analyze the shear behaviors of the pile-rock interface, an analytical solution of load transfer of pile at the crest of rock slope is obtained. To evaluate the accuracy of the new method, this method is compared with the results of finite difference analysis. Finally, the method is used to analyze the effect of slope, pile, and rock properties on the unit side resistance and axial force.

Model Test of Jacked Pile Penetration Process Considering Influence of Pile Diameter

In order to investigate the influence of different diameters on pile end resistance, pile side resistance, pile axial force and pile force transmission law of jacked pile penetration, two pairs of embedded sensitized microfiber grating sensors were installed by slotting the pile body. The pile-jacking process of static-pressing viscous foundation soil with different diameters of closed-tube model piles was successfully monitored. The test results show that the pile pressure, pile end resistance and pile side resistance of the two test piles increase linearly with the increase of pile depth. When the pile jacks, the final pressure of the test pile TP1 is higher than that of the test pile. TP2 is 31% higher, pile end resistance is 18% higher, and total side resistance is 57% higher. The results show that increasing the pile diameter can significantly increase the pile side resistance; under different penetration depths, the pile side resistance is from top to end. Continuously exerted, the axial force of the pile body decreases with the depth of the pile and the slope of the distribution curve of the axial forcegradually decreases. At the maximum penetration depth, the axial force of the pile TP1 is 18% larger than that of the test pile TP2; As the depth increases, the unit side resistance at the same penetration depth gradually decreases, that is, the side resistance has a “degradation effect”; at the end of the pile jacking, the percentage of the pile end resistance to the pile force exceeds 50%, that is, the pile end resistance bears most of the load. This research can be used as a reference for the study of pile driving mechanism in clayey and layered clayey soils.

Drilled shaft foundation construction problems

Various problems were encountered during the construction of three full-scale Drilled Shaft Foundations (DSF) at the Monticello Arkansas Test Site (MATS). These construction problems included, but were not limited to: loss of slurry, broken equipment and premature set-up of the concrete. Comparisons between the results obtained from the Bi-directional Load Cell (BLC) testing that was performed on each of the DSF aided in the determination of the effects of the construction problems on the axial capacity of the DSF. The measured unit end bearing resistance values were investigated to determine the effects of using a 1.2 m diameter clean-out bucket on a 1.8 m diameter DSF. In the South 1.2 m diameter DSF, the bottom plate of the BLC moved more than predicted (approximately 10 cm) due to the premature set-up of concrete below the BLC. Soil data obtained by using the Arkansas State Highway and Transportation Department (AHTD) and University of Arkansas (UofA) geotechnical investigation methods, in conjunction with the FB-Deep software program, were used to accurately predict the unit side resistance responses for the three DSF at the MATS. Therefore, the use of these geotechnical investigation techniques and this software programme are recommended for further use within the state of Arkansas. Due to the problems associated with maintaining an open DSF excavation overnight and the associated construction savings that may be obtained by constructing a DSF during a single day (for cohesionless soils), it is recommended that DSF be constructed (drilled and poured) in a single day.

The effect of sidewall roughness on the shaft resistance of rock-socketed piles

Piles socketed into rock are increasingly used to support loads from large-span bridges and heavy buildings. Peak side resistance is typically related to unconfined compressive strength, sidewall roughness and rock mass quality. This paper presents the results of tests on piles socketed in a weak, artificial rock made of sand, cement, gypsum powder and water. The test results are compared with methods of estimation in which the roughness of the pile–rock interface is modeled explicitly by assuming sinusoidal undulations along the interface. The testing program includes 10 model piles. Some of these piles have nonzero base resistance; others are unsupported at the base. The results indicate that both the degree of roughness of the socket sidewall and the base stiffness are of major importance to the load response of rock-socketed piles. The ultimate unit side resistance was observed to increase substantially with both increasing sidewall roughness and increasing base stiffness, but there is an upper limit to socket roughness beyond which very little increase in side resistance can be obtained. Most of the available correlations used to predict the ultimate side resistance of rock-socketed piles produced conservative estimates for the test piles in this study.

Developing a Model to Estimate Pile Setup for Individual Soil Layers on the Basis of Piezocone Penetration Test Data

This paper analyzes the results of 15 instrumented prestressed concrete test piles that were driven in four sites in Louisiana as part of a pile setup study. Static and dynamic load tests were conducted at specific time intervals to quantify the amount of setup after the end of driving. Laboratory and in situ soil investigations, such as the Piezocone penetration test (PCPT), were conducted at each test pile location to evaluate the subsurface soil condition. Vibrating wire strain gauges were installed in pairs in all instrumented test piles to measure the load transfer and increase in side resistance of individual soil layers over time. The load test results showed that setup followed a linear logarithmic trend. The unit side resistance, instead of the total pile resistance, was used to measure the logarithmic setup parameter A for individual soil layers along the pile lengths. Observations from the test results showed that the average A values for clayey and sandy soil layers for the four tested sites were 0.31 and 0.15, respectively. Analyses of the setup of individual soil layers showed that the parameter A decreases with increased corrected cone tip resistance measured by PCPT. A simple linear regression model is proposed to predict the side resistance setup for individual soil layers by correlating the setup parameter A with the corrected cone tip resistance.

Response of a drilled shaft foundation constructed in a redrilled shaft excavation following collapse

Two drilled shaft foundations (DSFs) of equal size (1.2 m diameter) were installed at the Turrell Arkansas Test Site (TATS). The soil stratigraphy at the TATS consisted of 6.1 m of clay underlain by 3.0 m of silt underlain by sand. After drilling the excavation for the North 1.2 m DSF, the silty soil collapsed from the sidewall of the excavation into the bottom of the excavation. Following the collapse, the excavation was redrilled and the construction of the DSF was completed. The measured capacity, unit side resistance, and end bearing resistance of the South 1.2 m diameter DSF were predicted by using software programs and mean values of soil data. The measured response of the North 1.2 m diameter DSF was backward modeled to determine the appropriate strength and stress reduction. Based on the measured data for this site, a 10 percent reduction in unit weight within the silt layer and a modification of the soil properties within the top 3.0 m of the sand layer produced predicted responses that matched t...

Load tests on drilled shaft foundations in moderately strong to strong limestone

AbstractThree drilled shaft foundations (DSFs) were constructed in moderately strong to strong limestone at the Siloam Springs Arkansas Test Site (SSATS). The embedment lengths within the limestone were 3·0, 1·5 and 2·1 m for the DSFs with diameters of 1·2, 1·8 and 1·2 m, respectively. The DSFs were instrumented to facilitate cross-hole sonic logging testing and full scale load testing using bidirectional load cells (BLCs). Lessons learned from construction included the: (1) proper concrete pouring techniques; (2) ability to retrofit improperly installed telltale instrumentation; and (3) influence of rock socket length within moderately strong to strong limestone. Recommended design, construction and testing techniques in moderately strong to strong limestone are presented. Based on the full scale testing, t–z model recommendations for weathered limestone and moderately strong to strong limestone are presented and discussed. Comparisons between measured unit side resistance and current design recommendati...

Three-dimensional numerical analysis of the stress transfer mechanism of XCC piled raft foundation

An X-section cast-in-place concrete (XCC) piled raft is a new type of foundation that uses piles with X-shaped cross-sections. Compared to a traditional circular cast-in-place concrete (CCC) pile, an XCC pile of the same cross-sectional area has a larger side resistance due to its larger cross-sectional perimeter. Although the pile capacity and load transfer mechanism of the XCC piled raft have been studied, the influence of this X-shaped geometry on the stress transfer between pile and surrounding soil is still not fully understood. To investigate the effects of the cross-sectional geometry, three-dimensional numerical analyses are conducted on an XCC and a traditional CCC piled rafts using the finite element method. The numerical results are verified by a field test of an XCC piled raft. Computed results reveal that lateral soil arching develops to a distance of approximately twice pile diameter surrounding the XCC pile, which can be demonstrated by the rotation of the principal stresses, leading to a non-uniform effective normal stress across a given cross-section and along the pile depth. The magnitude of the unit side resistance that acts on the concave surfaces of the XCC pile is up to twice the magnitude of the unit side resistance that acts on the flat surfaces. For a given applied load, the total side resistance mobilised on the XCC pile is usually larger than the total side resistance of the CCC pile, by a factor that ranges from 0.5 to 10, depending on the pile depth. Therefore, approximately 66% and 46% of the applied load is carried by the XCC and CCC piles respectively, and simultaneously, approximately 45% and 24% of the applied load is taken by the side resistance of the XCC and CCC piles, respectively. The larger effect of the XCC piled raft contributes to the cross-sectional geometry, which results in a larger perimeter and arching effects.

Roughness and Unit Side Resistances of Drilled Shafts Socketed in Clay Shale and Limestone

Rock socketed drilled shafts are being used increasingly to support heavily loaded structures. Rock sockets provide resistance to the load through a combination of side and base resistances. In this study, the effect of drilling tools such as an auger and a core barrel on the unit side resistance was investigated. A total of four field studies were performed on clay shale (compressive strength of 1–2 MPa ) and limestone (compressive strength of 10 MPa ). Borehole roughnesses produced by the different types of drilling tools in clay shale and limestone were measured using a laser borehole roughness profiler developed in this study to measure roughness to 0.5 mm in the boreholes. Based on the results of this study, it was observed that the drilling tools developed different socket roughnesses, which in turn affected the side resistances of the rock socketed drilled shafts.

Load Transfer Characteristics of Socketed Piles in Mumbai Region

This report uses load-transfer approach for analyzing the load-displacement response of piles socketed in weathered rocks typically found in Mumbai region. The field information used in the load-transfer analysis is obtained from conventional site investigations and does not necessitate elaborate tests. The load transfer behaviour of each stratum is expressed as a non-linear function. Empirical relations are used to express rock mass modulus and limiting values of unit side and base resistance in terms of unconfined compressive strength of intact socket material, which implicitly take into account the site-specific conditions. More than twenty pile load test data were back-analyzed before generalizing the governing parameters applicable to this region. This report demonstrates a wide range of applications of load transfer approach which includes the load-displacement behaviour and separation of elastic and net pile displacements.

Side Load-Transfer Mechanisms in Drilled Shafts in Soft Argillaceous Rock

Elastic-plastic axisymmetric finite-element analyses were performed to investigate the side load-transfer mechanism of drilled shafts socketed into cohesive intermediate geomaterials (very hard clays/very soft rocks). The roughness of the concrete-geomaterial interface was modeled explicitly by assuming sinusoidal undulations along a discontinuous surface. Smooth interfaces were also modeled. The results of the analyses indicated that the elastic response of rough sockets extends as the initial normal interface stress, σn, increases. Value σn does not affect the maximum unit side resistance, fmax, of sinusoidal sockets significantly, as shearing of the geomaterial occurs by gouging through the geomaterial asperities emanating from locations between the roots and crowns soon after separation occurs at the backs of the asperities. However, σn is a principal factor affecting fmax in smooth sockets. The sliding friction at the interface plays a major role in the development of load transfer, and internal friction of the geomaterial plays a less significant role. The behavior of smeared sockets was also investigated. A relatively small thickness of residual remolded geomaterial along a rough interface was found to reduce load transfer significantly.