Field Load Tests Research Articles

흙-못치기 공법을 적용한 사면의 거동 비교

흙-못치기 공법을 적용한 사면에 대해 법면을 숏크리트로 처리한 사면과 프리캐스트 콘크리트 전면판을 적용한 사면의 경우로 나누어 실물 현장시험이 수행되었다. 현장시험결과 얻은 하중-침하곡선을 비교해 볼 때 전면판을 적용한 경우 하중지지능력이 우수함을 알 수 있었다. 현장시험시 재하판에 가해진 총하중에 대해 재하판의 침하양상은 전면판을 적용한 경우 연성기초가 모래지반에 놓이는 경우와 같은 침하분포를 보인다. 숏크리트를 적용한 경우, 재하판의 침하량은 유사한 총하중 수준에서 전면판을 적용한 침하량에 비해 크고 부등침하의 경향도 크다. 전면판 적용시 보강면에 설치한 하중계에 의한 하중분포와 변형률계에 의한 계측결과, 재하판의 침하양상 그리고 경사계에 의한 수평변위양상을 종합적으로 고려해 볼 때 전면판을 적용할 경우 숏크리트를 적용할 때보다 국부적인 변위를 억제하고 보다 넓은 보강면에 하중을 분산시키는 것으로 생각된다. Full scale field load tests were conducted on two kinds of slopes reinforced with soil nail. One of the two slope is the slope with surface treated by shotcrete. The other slope has a surface placed by precast concrete panel. By comparing load-settlement curves, load bearing capacity for the case of pecast concrete panel was bigger than that for the case of shotcrete. Settlemet distribution of loading plate for the case of precast concrete panel was similar to that for the case in which flexible footing lies on sand. Settlement for the case of shotcrete was bigger than that for the case of the precast concrete panel and also was the differential settlement. By considering overall the test data of all the measurements related with load cell, strain gauge, settlement of loading plate and inclinometer, precast concrete panel has the advantage of load sharing in larger area and restriction of local displacement to the shotcrete treated case.

Applicability of the SPT-based methods for estimating toe bearing capacity of driven PHC piles in the thick deltaic deposits

Standard Penetration Test (SPT)-based design methods for pile foundations have been extensively used in Korean practice. However, their applicability for local application has seldom been examined, particularly for the thick deposits, such as in the Nakdong River deltaic area. This paper examines the applicability of three common SPT-based methods to deep sandy deposits in the delta. Routine SPT data, in which the test was completed for each of the N = 50 blows at less than 30 cm penetration in the last two increments of 15 cm, were adopted. A special SPT was conducted to examine the general relationship between penetration and blow counts in dense sands. Based on the special SPT and another well-documented case study, a simple linear extrapolation was developed to estimate data equivalent to N > 50. PDA (Pile Driving Analyzer) tests were also carried out to evaluate energy efficiency of the donut hammer used for the routine SPT. Energy correction factor (CE) was determined as 0.9. Using the corrected N-values, the estimated SPT-based toe resistances were compared with data obtained from PDA tests, field load tests on piles, and a CPT (Cone Penetration Test)-based method. Results indicate that the SPT-based methods generally manifest a rather low reliability. The recommended Meyerhof’s method is deemed applicable for the preliminary design.

Evaluation of In Situ Pavement Material Properties and Behavior through Field Instrumentation and Load Testing

State highway agencies have been experimenting with new concrete mixtures and pavement design features for improving the behavior and performance of concrete pavements. This paper presents the results of a field study undertaken in Maryland with alternative concrete mixtures. The objective of the study was to evaluate the in-place material properties for three concrete mixtures: a control, a fiber-reinforced, and a low-shrinkage concrete mix. Field instrumentation was used for monitoring the deflections and strains of the concrete slabs built with these concrete mixtures. Nondestructive testing (NDT) and back-calculation analysis were then used to evaluate the in situ material properties immediately after construction. Although traditional back-calculation analysis is based primarily on deflection measurements, in this study an iterative approach using NDT methods and measured strain and deflection data was employed for estimating the in situ modulus of subgrade reaction, k. This analysis provided a base ...

Performances of Compressive Capacity for Belled Wedge Pile Group

The belled wedge pile, which can improves the friction of pile shaft, tip resistance and reduce the influence of negative skin friction, is introduced. In this paper, the accuracy of FLAC3Dmodel is verified with field load test results. Subsequently, the numerical model was used to study the compressive behavior of belled wedge pile, conventional belled pile, wedge pile, and uniform section pile with the same concrete volume. Furthermore, the compressive behavior of belled wedge pile group was studied in terms of influencing factors such as pile spacing, stiffness of soil at the pile end, and diameter of enlarged pile head. The numerical results show that the compressive advantages of belled wedge pile can be developed adequately when the distributions of the friction of pile shaft and pile tip resistance are equilibrium, and it increases with increasing pile spacing, increasing stiffness of soil at the pile end, and increasing diameter of the enlarged pile head.

EVALUATION OF SIDE RESISTANCE CAPACITY FOR DRILLED SHAFTS

This paper presents an extensive evaluation of axial side resistance of drilled shaft foundations. A wide variety of load test data are used and these data are divided into drained and undrained databases. Representative analytical models, including alpha (α), beta (β), and lambda (λ) methods, are examined in detail using both measured and predicted results to assess their relative merits for the drilled shaft design. Based on these analyses, the undrained shear strength (α-s(subscript μ)) correlations have exhibited better statistics for undrained side resistance prediction, and the undrained strength ratio (α-USR) correlations can be adopted as an alternative analytical method, especially in the case of smaller s(subscript μ). For β method, the stress factors (K/K(subscript o)) are developed from the back-analysis of field load tests. However, the β method has presented more varying results for short shafts in both drained and undrained loading. Among all analytical methods, the λ method is relatively the less reliable prediction model. Specific design recommendations for side resistance analysis of drilled shaft are suggested.

Behavior and Simulation of Deep Cement Mixing (DCM) and Stiffened Deep Cement Mixing (SDCM) Piles Under Full Scale Loading

A new kind of Deep Cement Mixing (DCM) pile called Stiffened Deep Mixing Pile (SDCM) is introduced to mitigate the low flexural strength and unexpected failures of DCM piles. A jet grouting method with a jet pressure of 22 MPa, was utilized in the installation of DCM piles. The SDCM pile consists of a DCM pile with a precast reinforced concrete core pile inserted at its center. Pile and embankment load tests were conducted, and then the results of the field load tests were simulated by a 3D finite element method (FEM) to back-analyze and confirm the related design parameters. These parameters were then used further in numerical experiments. The field test results showed that the settlements and lateral movements of the SDCM pile using a prestressed concrete core pile with area ratio ( A core / A DCM ) of 0.17 and a length ratio of 0.85 was less than those of the DCM pile by 40% and 60%, respectively. Moreover, the SDCM pile foundation increased the bearing capacity by as much as 2.2 times. The average lateral pile capacity of the SDCM piles was 15 times higher than the DCM piles. A strength reduction factor of 0.40 was obtained at the concrete core and the DCM interface from the full scale pullout test. The behavior of both the DCM and SDCM piles was confirmed from the subsequent 3D FEM simulations. From the 3D FEM simulations, the length of the concrete core pile had more influence on the settlements of the SDCM pile than its cross-sectional area. However, both the length and cross-sectional area of concrete core pile affected the lateral resistance of the SDCM pile.

Analysis of anchor foundation with root caissons loaded in nonhomogeneous soils

This paper presents a novel type of deep foundation — an anchor foundation with root caissons, which improve the soil–caisson interaction using penetrating roots. A simplified analytical procedure is proposed for calculating responses of the new anchor foundation subjected to combined vertical, horizontal, and moment loadings. Caisson–soil interaction is simulated by a Winkler subgrade reaction model, with an improved Winkler spring constant to consider the reinforcement effect of roots. The method incorporates limiting soil stress to investigate soil nonlinear behavior and a transfer matrix to represent nonhomogeneous soils, with a passive caisson model accounting for group effects. The effectiveness of the present approach is evaluated by comparison with full-scale field load tests and a finite element analysis on a small-scale anchor foundation to give a preliminary design guideline for the Ma’anshan Yangtze River Bridge in China.

연약 암염층(Sabkha)에 보강된 스톤컬럼의 침하거동에 관한 해석방법 비교연구

본 논문에서는 일련의 현장시험과 수치해석을 통해 연약 암염층(Sabkha)에 보강된 스톤컬럼의 침하거동 특성을 평가하였다. 스톤컬럼으로 보강된 복합지반의 침하거동특성을 평가하기 위해 Saudi의 Kayan 지역에 시공된 스톤컬럼에 대한 현장 재하시험을 수행하였다. 스톤컬럼의 보강효과를 평가하기 위해 현장시험결과와 Pribe의 간편법, 그리고 수치해석 결과를 상호 비교 분석 하였다. 수행된 연구결과, Priebe 제안식으로 산정한 침하량은 스톤컬럼이 시공된 실제 현장의 침하량보다 과다하게 평가함을 확인하였다. 또한, 수치해석을 통해 스톤컬럼이 보강된 복합지반의 거동을 예측할 때, 주변에 시공된 스톤컬럼들의 구속에 의한 지지력이 향상되는 효과를 적절히 고려해야 함을 알 수 있었다. In this study, a composite behavior of stone columns reinforced in a soft ground, Sabkha, has been evaluated by performing a series of field measurements and numerical analyses. Field load tests were performed to verify the effect of the composite ground reinforced by stone columns in Kayan, Saudi. The settlement measured in the field test was compared with the settlement calculated by the Priebe method and the numerical analysis using ABAQUS. It is found that the settlement estimated using the Priebe method significantly overestimated the settlement measured in the field test. In addition, it is confirmed that consideration of confining effect exerted by surrounding adjacent stone columns in a numerical simulation is indispensable to estimate accurately the settlement of stone column composite ground.

Analysis of soil resistance on laterally loaded piles based on 3D soil–pile interaction

The load distribution and deflection of large diameter piles are investigated by lateral load transfer method ( p– y curve). Special attention is given to the soil continuity and soil resistance using three-dimensional finite element analysis. A framework for determining a p– y curve is calculated based on the surrounding soil stress. The appropriate parametric studies needed for verifying the p– y characteristic are presented in this paper. Through comparisons with results of field load tests, the three-dimensional numerical methodology in the present study is in good agreement with the general trend observed by in situ measurements and thus, represents a realistic soil–pile interaction for laterally loaded piles in clay than that of existing p– y method. It can be said that a rigorous numerical analysis can overcome the limitations of existing p– y methods to some extent by considering the effect of realistic three-dimensional combination of pile–soil forces.

Load testing and GPR assessment for concrete bridges on military installations

The US Army owns and maintains approximately 2000 bridges on its installations spread out in the United States and around the world. From this inventory, 67% are concrete bridges, most of which do not have design or as-built plans to effectively evaluate their condition/capacity. In addition, military vehicles have unique characteristics that are difficult to take into account when analytical analyses are performed. For these purposes, the US Army Engineer Research and Development Center has been adapting non-destructive techniques. The most promising concept explored thus far involves bridge rating through non-destructive load testing in combination with Ground Penetrating Radar (GPR) techniques. Field load testing techniques are valuable for evaluating the capacity of existing bridges and accurately characterize the structure’s live-load response while GPR techniques provide valuable information regarding the internal reinforcement as well as the condition of the concrete. This article will provide a brief description as well as the results from recent evaluations performed on reinforced concrete bridges at military installations.

Full-Scale Field Load Testing of Storm-Water Storage Chamber Structures

One of the latest solutions available for storm-water storage purposes is the underground chamber structure. Recently, a research team at Ohio University conducted a series of field load tests on the underground chambers. Four chamber structures were placed side by side in an excavated area, backfilled with coarse granular soil, buried under a soil cover of 0.46 m (18 in.), instrumented with sensors, and subjected to a series of controlled live load tests at a field project site. The sensor readings and visual inspection results indicate that the chamber with the specified minimum soil cover had no problem in supporting a wheel load of 52.3 kN (11.8 kips) and an axle load of 109.0 kN (24.5 kips) in both the transverse and longitudinal directions. Maximum reduction in the rise dimension was only approximately 2.3% when the chambers were subjected to the live loads. The vertical soil pressure readings measured at the chamber crowns were within 15% of the values given by a live load spreading formula include...

Relationship between Texas Cone Penetrometer Tests and Axial Resistances of Drilled Shafts Socketed in Clay Shale and Limestone

Modern methods for designing drilled shafts in soft rock require knowledge of the compressive strength and modulus of the rock. However, rock jointing at many sites prohibits the recovery of samples of sufficient length and integrity to test rock cores in either unconfined or triaxial compression tests. Since rational design procedures usually require values of compressive strength, surrogate methods must be employed to estimate the compressive strength of the rock. The surrogate methods considered in this study was Texas cone penetrometer tests, and performed at several sites in North Central Texas. In order to develop the relationships between Texas cone penetrations and side and base resistances of rock socketed drilled shafts, three field load tests were conducted. Based on the field study and literature reviews, a relationship between Texas cone penetration tests and axial resistances of rock socketed drilled shafts was proposed.

Point bearing stiffness and strength of socketted drilled shafts in Korean rocks

The load distribution and deformation of rock-socketted drilled shafts subjected to axial loads were evaluated via a load-transfer approach to quantify the point bearing load transfer characteristics of rock-socketted drilled shafts based on Hoek-cell triaxial compressive tests and a three-dimensional numerical analysis with varying rock strengths and rock mass conditions. It was found that the ultimate unit point resistance ( q max ) was influenced by rock mass discontinuities; moreover, the initial tangent of the point bearing load transfer curve ( G i ) was highly dependent on the rock mass modulus and pile diameter. Thus, a point bearing load transfer function for drilled shafts socketted into rock is proposed. Through comparison with the results of field loading tests, it was found that the point load transfer function proposed in the present study is in good agreement with the general trend observed by field loading tests.

Design, test and field application of a GFRP corrugated-core sandwich bridge

This paper describes the design procedures and the construction process of a glass fiber reinforced polymer (GFRP) corrugated-core sandwich bridge superstructure. This all-GFRP bridge superstructure was installed in Korea. Based on field load testing and finite element analysis, the effectiveness of the proposed system was demonstrated. The paper also discussed connection details as well as the dynamic effects on the FRP sandwich superstructure due to truck live load. Finally this paper illustrated the time, labor, and cost invested in the project and explained why bridges with FRP superstructures can be economically competitive in the future.

CALIBRATION OF TSUNAMI LOADING ON A DAMAGED BUILDING

The survival of a large number of buildings in southern Thailand with minor structural damage under 2–6 m inundation heights above the ground in the 2004 Indian Ocean tsunami tragedy suggests that it is necessary to calibrate the formulas stipulated by FEMA-55 [2000] for computing tsunami loadings. In this study, the weather monitoring building of the Meteorological station at Takua Pa, Phang Nga is used as the case study. The building suffered only minor structural damage to the columns and girders. However, most of the nonstructural members such as infill brick panels were damaged, except a few which contributed to significant reserve strength against the tsunami attack. The FEMA-55 loading is calibrated with the actual building performance from a field load test. The maximum velocity that occurred at the site in that event is assessed, and a velocity suitable for computation of tsunami load for southern Thailand is recommended.

An oil sand pseudo-elastic model for determining ground deformation under large mobile mining equipment

Strain softening of oil sand under dynamic loading from large mining equipment inhibits the ability of the equipment to function at optimal design performance. This paper looks at the findings of dynamic plate load tests, which effectively mimick the loading and unloading action of a shovel track pad. A pseudo-elastic model was proposed based on the results of the dynamic plate load testing to predict the deformation of oil sand under cyclic loading. Both field and laboratory cyclic plate load tests were performed on oil sand materials. The field tests were performed with different plate sizes, or footprints. The load was normalized based on the pressure stiffness concept in units of pressure per unit deformation. FLAC was used to model the field plate load test deformation with the elastic concept. The laboratory tests were performed at room temperature with more control on the load, loading rate, and cycles than possible during the field testing. Tests were conducted using a circular plate of 14.9 cm diameter, at stress magnitudes of 200, 400, 500 and 600 kPa. The plate load tests were conducted for varying loads, holding, and relaxation times of 0, 2, 5 and 10 min respectively for each magnitude of stress. The outcome of laboratory plate load tests show that after frequent cycles, the pressure stiffness (ratio of stress to deformation) converges on a plateau value of 8 kPa/mm. The proposed approach can be used to evaluate oil sands ground performance, enhancing the prediction process for ground deformation under the operation of ultra-class mining equipment.

Damage condition and field loading test of the continuous non-composite I-girder steel bridge with deck joints used for about 50 years

Damage condition and field loading test of the continuous non-composite I-girder steel bridge with deck joints used for about 50 years

Crack Detectability and Durability of Coaxial Cable Sensors in Reinforced Concrete Bridge Applications

The working mechanism and the measurement principle of topology-based crack sensors made of coaxial cables are briefly reviewed. The sensitivity, spatial resolution, and ruggedness of two coaxial cable sensors, respectively made of rubber and Teflon dielectric materials, were compared and validated with laboratory testing of a 4/5-scale, T-shaped, reinforced concrete beam-column specimen. Two Teflon sensors were installed on one of the solid decks of a three-span continuous highway bridge to investigate their durability and measurement repeatability. Laboratory tests indicated that both types of sensors have high sensitivity, but the Teflon sensor has a higher spatial resolution and a negligible spillover effect of any significant cracks. At a 90-degree bend, however, the Teflon sensor is more susceptible than the rubber sensor to the rubbing action of the outer conductor of a coaxial cable against its dielectric layer. No cracks were observed during the field load tests of the instrumented bridge. Both sensors indicated high durability in real-world application but a certain variation of waveforms was measured over a period of 5 years because of the use of different instruments. Future research is directed to develop an online calibration of crack sensors with a small portion of built-in standard cable at the end of the cable sensor.

Behaviour of geosynthetic-encased granular columns in porous collapsible soil

ABSTRACT: The construction of embankments on soft saturated soils can be a challenge due to the low shear strength and high compressibility of these soils. The same may be true for constructions on porous collapsible soils, because the collapse of the soil structure can lead to large foundation soil deformations leading to damage to the embankment, particularly in the case of bridge abutments. Conventional piles and granular columns have been used to stabilize such embankments when there are limits for embankment settlements. More recently, geosynthetic-encased granular columns have been increasingly used as an alternative solution. This study examined the performance of geosynthetic-encased columns for the stabilization of embankments on porous collapsible structured unsaturated soil. Field load tests were performed on conventional sand and gravel columns and on geotextile-encased sand columns and on geogrid-encased gravel columns. During testing, the collapse of the surrounding soil was induced by water injection through the granular column top to investigate the influence of the casing on the column performance. The results obtained show that significant increases on pile load capacity can be obtained depending on the materials used and construction conditions. The effects of foundation collapse can also be reduced with the use of a geosynthetic casing in the granular column.

Axial Compression of Footings in Cohesionless Soils. II: Bearing Capacity

An extensive database of full-scale field load tests was used to examine the bearing capacity for footings in cohesionless soils. Each load test curve was evaluated consistently to determine the in...