Rock Socketed Research Articles

Load-bearing Behavior of Offshore Rock Socketed Monopile Foundation Regarding Different Rock Mass Classification

With the increasing electricity demand in China, wind power has been heavily developed in recent years. It is important to stabilize the wind turbine foundations in rock bedded near the sea area while installation. Based on different rock classification standards (GB 50218 and GSI), this paper numerically analyzed the load capacity of rock socketed monopile. When the rock class is high (class III and above), under effective socketed depth, the rock-socket effect is important, and the pile tip deflection is nearly 0, which could be considered as a clamping constraint. In this case, even if the rock quality around the pile tip decreases a little or becomes a little weakened, the pile deformation and internal force will not change a lot. However, when the rock mass class is lower than IV, the pile tip load capacity will largely decrease. The definition of rock mass parameters is also important when analyzing rock socketed monopile. In conclusion, it is suggested to take GB 50218 as a reference. BQ engineering rock mass classification and its corresponding rock mass parameters could be applied. Also, the M-C model is suggested to be used for some related work.

Optimization of Empirical Methods in Determining the Load Capacity of Rock Socketed Piles

Optimization of Empirical Methods in Determining the Load Capacity of Rock Socketed Piles

Side Resistance of Drilled Shafts in Weak Fine Grained Sedimentary Rock

Load transfer mechanism in side resistance of rock socketed drilled shafts has been studied for the past four decades using results of axial load tests and theoretical methods. Various models for prediction of side resistance have been proposed. Only few studies (e.g., Horvath et al. 1983; Rowe and Armitage 1987; Hassan et al. 1997, Miller 2003, Abu-Hejleh et al. 2003) have been completed on socket side resistance of drilled shafts in weathered and fractured fine-grained rock. These studies, however, were based on only a limited number of load test data. A survey of current predictive models has been conducted. This survey shows most of the current models include strong and intact rocks in their databases. Almost all of the current models use a power function to correlate side resistance of rock socket to rock unconfined compressive strength. A database of side resistance of large diameter drilled shafts in only weak fine-grained rocks, such as, weak shales, mudstones, and siltstones (i.e., Intermediate Geomaterial first introduced by O’Neil et al. 1996, Hassan et al. 1997, and O’Neill and Reese 1999) has been complied in this study. The range of weak rocks considered herein corresponds to an unconfined compressive strength of 0.48 to 4.8 MPa. Analysis of this database shows that a linear model best predicts the side resistance of drilled shafts in weak fine-grained sedimentary rocks.

Estimation of lateral capacity of rock socketed piles in layered soil-rock profile

Large diameter rock socketed piles were preferred for the purpose of transmission of a huge volume of both vertical and lateral load from superstructure to a deeper depth safely without any structural defects. A series of experimental program was conducted on model pile for studying the behaviour of the rock socketed pile under static lateral load in a soil-rock layered profile system. The model piles were instrumented with displacement and force transducers for measuring the magnitude of the pile movement and load transferred by the pile. The experimental results showed that the rock socketed pile lateral capacity has significantly affected by the depth of embedment of the pile in soil and depth of rock socket. There was a considerable increase in the lateral capacity of the pile when the depth of socketing is three times the diameter of the pile into rock with a minimum embedment. In the 3D socketed piles, the lateral capacity of the pile is almost 18 times higher than the non-socketed piles. From the experimental study, it is also observed that when the piles socketed more in to the hard strata (rock), the depth of fixity increases and the lateral displacement reduces substantially.

Revisiting Methods for the Design of Rock Socketed Piles

AbstractThe three principal methods specifically developed for the design of rock socketed piles were originally presented in the 1980s. One of the methods is an empirical technique based on the no...

Evaluation of peak side resistance for rock socketed shafts in weak sedimentary rock from an extensive database of published field load tests: a limit state approach

This paper presents analyses of the measured peak side resistance of rock sockets constructed in weak claystone, shale, limestone, siltstone, and sandstone. The peak side resistance is obtained from in situ axial load tests on drilled shafts, anchors, and plugs. The parameters that affect the development of peak side resistance are determined using in situ load test data. It is found that peak side resistance increases with the unconfined compressive strength and deformation modulus of the weak rock, and decreases with the increase in length of the shear surface along the rock socket sidewalls. The increase in socket diameter also slightly decreases the peak side resistance. Additionally, it is found that the initial normal stresses do not significantly affect the measured peak side resistance in the in situ load tests. The in situ load test data are used to develop an empirical design equation for determination of the peak side resistance. The proposed model for peak side resistance and the reliability analysis are used to determine the corresponding resistance factors for use in the load and resistance factor design framework for assessment of the strength limit state.

Analysis of Bearing Capacity of Rock Socketed Pre-Bored Super Strength Piles Based on Dynamic Load Test Results

Analysis of Bearing Capacity of Rock Socketed Pre-Bored Super Strength Piles Based on Dynamic Load Test Results

Load Distribution Behaviour of Bored Pile in Various Soil Formation: Rock Socket in Limestone, Schist and Sandstone

Rock socketed bored pile is a solution when the load from the structure is very high and/or accessible bearing surface hasan inadequate bearing capacity. The study is based on instrumented bored pile socketing into different types of rock namely.limestone, schist and sandstone at three sites. The result for three (3) test piles namely PTP1, UTP-1 and TP2 shows most of the load are resisted by friction rather than end bearing at the pile working load. The load apportioned to end bearing at higher loads varies for the three test piles. Comparison of observed mobilised skin friction in the rocks with empirical methods indicates that prediction values from Williams and Pells [1] over design for two out of the three test piles and that by Hovarth [2] are under design for two out of the three test piles.

The Soft Rock Socketed Monopile with Creep Effects – A Reliability Approach based on Wavelet Neural Networks

AbstractIn the present study the numerical model of the pile embedded in marl described by a time dependent model, based on laboratory tests, is proposed. The solutions complement the state of knowledge of the monopile loaded by horizontal force in its head with respect to its random variability values in time function. The investigated reliability problem is defined by the union of failure events defined by the excessive horizontal maximal displacement of the pile head in each periods of loads. Abaqus has been used for modeling of the presented task with a two layered viscoplastic model for marl. The mechanical parameters for both parts of model: plastic and rheological were calibrated based on the creep laboratory test results. The important aspect of the problem is reliability analysis of a monopile in complex environment under random sequences of loads which help understanding the role of viscosity in nature of rock basis constructions. Due to the lack of analytical solutions the computations were done by the method of response surface in conjunction with wavelet neural network as a method recommended for time sequences process and description of nonlinear phenomenon.

Static Load Tests in an Instrumented Rock Socket Barrette Pile

The foundation for the new Petrobras headquarters building in Salvador, Bahia, northwest of Brazil, had barrette pile rock socketed units chosen as the best engineering solution, due to shallow top rock, given schedule and cost. Even though the soil strata was stiff to very stiff silt, the required design load was not able to be based on soil side resistance only, resulting in a rock socket design. A 300 kPa ultimate shear stress was assumed by the designers and static load tests were performed to verify this parameter. This paper evaluates the results obtained from the test without discussing the designer assumption. Rock socket shear stress verification was made possible by placing an expanded polystyrene block below the pile steel cage, eliminating any possible bottom resistance. Beyond the usual top instrumentation, electric retrievable extensometers were installed along the shaft to afford depth load transfer evaluation. This paper presents the results of the load tests as well as an application of analytical and semi-empirical methods available in the literature to prove their usefulness and effectiveness, revealing and confirming many aspects of field behavior.

Numerical Simulation Analysis of Bearing Characteristics on Super-Large Diameter Rock Socketed Pile

Wujiang Bridge is located on the Wujiang River in Chongqing Province in China. Based on test method of numerical simulation, the bearing characteristics of this large-diameter rock-socket pile with super-thick pile caps have been analyzed, including pile foundation load-bearing characteristics, pile-soil load sharing, and stress flow analysis of thick pile caps. The results indicated that Q-s curve of this kind of pile is approximate to linear. Under the action of ultimate load, the main load was supported by pile end résistance. And according to main stress distribution of pile cap, there is an obvious spatial truss effect phenomenon in it.

Lateral Load Capacity of Rock Socketed Piers Using Finite Difference Approach

In the present work it has been proposed to study the pier foundation of bridge supported on two piers. The piers are situated on left and right bank of river. The rocks present at site indicate presence of lower Shiwalik rocks with alteration of sandstone/ clay rocks. A finite difference scheme is used to analysis the pier rock socket foundation. A computer code is developed in FORTRAN 90 to determine the displacements and stresses at each node of discrtized rock domain. By using this methodology lateral load capacity of rock socketed pier foundation is to be determine.

Calculation Method for the Socketed Length of the Rock Socketed Pile by the Settlement of the Pile Top

AbstractThe load transferring mechanism was investigated and then used to establish the load transferring equation. A calculation method for the vertical load transferring characteristic of the rock socketed pile was proposed to make up for the deficiency of that method in current norms. This method can derive not only the expression of the socketed length of pile, but also the load sharing ratio at the pile tip. Case histories were used to observe the variation of the socketed length and the load sharing ratio at the pile tip over the settlement at the pile top. The results indicate that the required socketed length increases as the settlement requirement at the pile top decreases. The larger the settlement at the pile top, the higher the load sharing ratio at the pile tip. The increment of the socketed length ratio results in the descent of the bearing ratio of the pile tip resistance when other conditions remain unchanged. The method can determine the socketed length of the pile both safely and economi...

Kinematic and Inertial Effects of Earthquakes on Rock Socketed Single Piles in a Two-Layered Medium

The behaviour of piles in a two-layered soil medium subjected to earthquake ground accelerations are investigated using finite element method. The kinematic and inertial effects on rock socketed piles in a two-layered soil medium are investigated in this study considering the soil properties relevant to Sri Lanka. Hyperbolic nonlinear constitutive model is used for modelling the behaviour of the fully coupled soil medium. The effect of the earthquake was simulated by lateral ground acceleration applied to the bedrock and in this respect two earthquake records measured at a considerable distance away from the epicentre are used in the numerical simulation to take into account large epicentral distance to an anticipated earthquake that might affect Sri Lanka. The validity of the results of the proposed model was established by comparing with the trends observed in similar studies reported in the literature. A detailed parametric study of the kinematic bending moments developed in piles at the layer interface of the two-layered medium is carried out using the developed model. Furthermore, the effects of the inertial forces on the kinematic bending moment developed at the layer interfaces are investigated by varying the pile diameter and the effective masses at the pile head. Moreover, the variation of the bending moments, developed in the pile due to the combined effects of the kinematic and inertial responses of the pile-soil system, with the effective mass at the pile head for different pile diameters is also investigated.

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.

A New Approach to Estimate Side Resistance of Rock Socketed Drilled Shafts

The uniaxial compressive strength of intact rock is widely used as the sole factor to estimate the side resistance of drilled shafts socketed in rock. However, the side resistance should also depend on in situ rock mass characteristics such as rock type, strength, joint frequency, and weathering conditions. In this study, a new approach is proposed to estimate the side resistance of rock socketed drilled shafts. The approach is based on the GSI rock mass classification, and the Hoek and Brown failure criterion. Inclusion of all these factors into the proposed method explains, to some extent, the differences that are obtained when various empirical methods are used. Comparisons between observed side resistances from field case studies and estimated side resistances with the proposed method show a good correlation. The method appears to be robust since the results are relatively insensitive to estimation from the different rock mass classification and properties and are comparable with predictions from previous empirical correlations.

Side resistance rock sockets in sandstone, mudstone, and shale

The fundamental parameters of rock strength, rock mass stiffness, and interface roughness that control the development of side shear in a rock socketed pile are discussed on the basis of results from laboratory model socket tests, constant stiffness direct shear tests, and instrumented prototype piles. Based on the understanding of these fundamental parameters and on a survey of socket field test results, an empirical design method is proposed for side shear only sockets. This design method considers both the maximum load capacity and settlement criteria for single sockets.