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Seismic retrofitting of existing bridges has been in practice for years to meet the stringent seismic requirements set forward by revised design codes. For retrofitting, however, bridge piers are often prioritized while less attention is given to the bridge foundations, which are equally prone to damage under seismic loadings. The current work presents a series of experimental studies in assessing the performance of 2 × 2 pile groups reinforced with micropiles in terms of head-level stiffness and damping under low-to-high levels of static and dynamic loadings, encompassing the influence of loading-induced soil nonlinearity. Practical micropiles inclinations of 0°, 5°, and 10° with respect to the vertical are studied. Experimental results reveal that the head-level stiffnesses of pile groups reinforced with micropiles, contrary to the general expectations, become smaller than the pile group without micropiles at higher levels of applied loading. To elucidate the governing mechanism for such experimentally obtained results, three-dimensional nonlinear finite-element analyses were carried out. Results from the numerical analyses support the experimental results, suggesting that the presence of micropiles may not always increase the head-level stiffness of soil–foundation systems, particularly at higher levels of applied loading where the soil nonlinearity generated at the vicinity of piles and micropiles governs the overall head-level stiffnesses. [ABSTRACT FROM AUTHOR]

AbstractThe application of anchor cable micropile group (ACMPG) in small and medium-sized slope support is gradually widespread. However, the coordination deformation of the structure and the resistance of the soil in front of the piles are less considered in the existing calculation models. Therefore, based on the load transfer approach and according to the structural characteristics of the ACMPG, the calculation method was provided for the resistance of the soil in front of the pile and the tension of the anchor after deformation. And the equations for calculating the resistance of the ACMPG were established. Based on the method of upper bound limit analysis, the display equation had been established for the safety factor of reinforcing the 3D slope of the structure. And finite element models were developed to validate the theoretical model. Finally, a parametric study was conducted to investigate the influence of slope angle, soil friction angles, location, 3D effects, on the slope safety factor and the support effect of piles and anchor cables supporting the structure. The results showed that the theory proposed in this paper can accurately calculate the safety factor of slopes, which is helpful for the design and construction of slope reinforcement. [ABSTRACT FROM AUTHOR]

Micropile groups (MPGs) are typical landslide resistant structures. To investigate the effects of these two factors on the micropile–soil interaction mechanism, seven sets of transparent soil model experiments were conducted on miniature cluster piles. The soil was scanned and photographed, and the particle image velocimetry (PIV) technique was used to obtain the deformation characteristics of the pile and soil during lateral loading. The spatial distribution information of the soil behind the pile was obtained by a 3D reconstruction program. The results showed that a sufficient roughness of the pile surface was a necessary condition for the formation of a soil arch. If the surface of the pile was smooth, stable arch foundation formation was difficult. When the roughness of the pile surface increases, the soil arch range behind the pile and the load-sharing ratio of the pile and soil will increase. After the roughness reaches a certain level, the above indicators hardly change. Pile spacing within the range of 5–7 d (pile diameters) was suitable. The support effect was poor when the pile spacing was too large. No stable soil arch can be formed, and the soil slips out from between the piles. [ABSTRACT FROM AUTHOR]

Micropiles are often implemented through drilling, steel pipe installation, reinforcement and grouting. However, in some parts of the world, especially in areas with fine-grained soils, these shafts are implemented by steel pile driving, followed by reinforcement, and grouting has been expanded considerably. In this study, micropile shafts were installed at the site by both driving and drilling methods. Reinforcement and grouting were carried out by two-step grouting and applying different grouting pressures in the micropiles. Some boreholes (at a distance of 0.3 m from the micropile axis) and test pits were drilled to investigate the penetration radius of the grout at different grouting pressures. Results showed that the bearing capacity of driven micropiles is about 4 to 14% more than that of drilled micropiles due to the soil compaction impacts. The average uniaxial compressive strength of the soil samples after micropiles grouting was dependent on the applied grouting pressure and increased from 25 to 56%. In addition, the direct shear test results showed an increase of 15% in the soil cohesion and an increase of 4° in the internal friction angle for the soil after grouting of the micropiles. [ABSTRACT FROM AUTHOR]

Soil investigation is very important to check the bearing capacity before constructing any structure. There are different types of soils that cause many problems for the structure in short and long term, which are known as problematic soils. A lot of researchers dealt with improvement and reinforcement of the problematic soils by physical and chemical treatments. The objective of this study is reinforcing the problematic soil with micropiles with different depths and different configurations. In this study, two types of soils, soft clay and loose sand, were used to study the effect of adding micropiles of different depths and different configurations to investigate the best improvement of bearing capacity for shallow foundations on these soils. The results showed that reinforcing the natural soil with micropiles could improve the pressure carrying capacity of the problematic soils. When the design width is changed from under foundation alone to under foundation and 2B width, the soil reinforced with 2B depth of micropiles can raise the soil’s load carrying capacity by 45 to 65% when compared to untreated soil. Just 7% more bearing capacity may be achieved by increasing the depth of the micropiles from 2B to 3B (where B is the footing width); as a result, going deeper than 2B is not advantageous. Additionally, the bearing capacity of the micropiles increases by only 3% when the breadth of the configuration is increased from 1B to 2B; so, wider configurations than 1B are invalid.

Purpose is to identify vertical displacements of the "soil basem strengthened with piles or micropiles based upon drilling-mixing technology" system relying upon parametric analysis of strain state of the mentioned system, and arrangement of the strengthening elements. Methods. Mathematical modeling took place for twelve finite-element models using the computing complex SCAD intended to analyze strength of structures by means of finite-element method. Numerical analysis was carried out with variation of elastic-strain modulus of vertical reinforcing elements and change in distance between them (3d and 6d of micropiles). Findings. Results of parametric analysis have been obtained for a model without a micropile (non reinforced soil base); a model with a single micropile; a model with two micropiles where distance between them is 1.5 m, i.e. 3d of micropiles; and a model with two micropiles where distance between them is 3.0 m, i.e. 6d of micropiles. The performed comparative analysis has made it possible to obtain the results proving the hypothesis by the authors as for the specific nature of vertical displacement formation of the "soil base strengthened with piles or micropiles based upon drill-mixing technology" system. Originality. It has been identified for the first time that basing upon the standardized document for the auger or displacement piles, it is impossible to decrease efficiently vertical displacements while approaching micropiles since distance between the micropiles is 3d for elements, developed on the basis of the drilling-mixing, is minimal. Practical implications. The obtained results of a strain state may become the keystone for the development of the generalized strain theory of the composite "soil base strengthened with piles or micropiles based upon drilling-mixing technology" system as a medium differing in minor changes of strain characteristics. [ABSTRACT FROM AUTHOR]

Micropile groups (MPGs) are typical landslide resistant structures. To investigate the effects of these two factors on the micropile–soil interaction mechanism, seven sets of transparent soil model experiments were conducted on miniature cluster piles. The soil was scanned and photographed, and the particle image velocimetry (PIV) technique was used to obtain the deformation characteristics of the pile and soil during lateral loading. The spatial distribution information of the soil behind the pile was obtained by a 3D reconstruction program. The results showed that a sufficient roughness of the pile surface was a necessary condition for the formation of a soil arch. If the surface of the pile was smooth, stable arch foundation formation was difficult. When the roughness of the pile surface increases, the soil arch range behind the pile and the load-sharing ratio of the pile and soil will increase. After the roughness reaches a certain level, the above indicators hardly change. Pile spacing within the range of 5–7 d (pile diameters) was suitable. The support effect was poor when the pile spacing was too large. No stable soil arch can be formed, and the soil slips out from between the piles.

Micropiling is an extensively used method for improving the stability of building foundations and load-carrying capacity of the soil. Unlike regular piling, it can be employed without pile driving equipment and, hence, it is a versatile option of soil reinforcement under space-restricted situations. Since, it is an economical and easy to implement option for soil improvement, this paper intends to study the improvement in bearing capacity and settlement behaviour of a fly-ash bed using fine micropiles under isolated footings, for low-cast and lightweight structures. Fly-ash, a by-product of coal-fired power plants, is used in the experiment because it is extensively used as a filling material for housing projects in low-lying areas and pavements. Micropiles were installed underneath the footing as well as beyond the periphery of footing with varied spacing and extent ratio. The results are depicted through two dimensionless constants, namely bearing capacity ratio (BCR) and settlement reduction factor (SRF). Significant improvements have been observed in load-carrying capacity and settlement potential due to decrease in spacing and increase in lateral extent of micropiles. The optimum configuration of spacing and lateral extend achieved 135% bearing capacity improvement with 71% decrease in settlement. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study summarizes the engineering design and calculation methods of micropiles and proposes a pile length optimization model based on numerical simulation software. Based on the proposed micropile calculation method and optimization method, a specific analysis of a project example was carried out, and a series of calculations, such as micropile design calculation and pile length optimization for the project, was completed. The results show that the miniature pile length optimization model based on numerical simulation finite difference method improves the previous method by automating the optimization process through fast modeling, automatic creation of optimization commands, and output and analysis of optimization results, and realizes the optimization of pile length using numerical simulation, which improves the efficiency of the optimization of the pile length under the premise of guaranteeing accuracy, and achieves the unity of both efficiency and accuracy. The feasibility of this optimization process is proved by engineering examples. The engineering practicability of the micropile design calculation method and optimization method proposed in this study is proved through practice. It provides a reference value for the initial fast and flexible management of small landslides. [ABSTRACT FROM AUTHOR]

The interaction mechanism between micropiles and soil landslides is comprehensively investigated through static model tests and numerical simulations. The results show that the deformation damage mode of micropiles is mainly bending and shear damage. Because of bending deformation, cracks appear at the rear and front of the pile, respectively, about three times the pile diameter from the sliding surface. In addition, the plastic damage becomes more severe when approaching the back edge of the landslide body. Micropiles in the landslide body play a significant role in load sharing; more importantly, there is a certain pattern between the miniature piles. According to the experimental and numerical simulation results, the recommended load-sharing ratio for micropile design under static conditions is as follows: rear-row pile:middle-row pile:front-row pile = 0.411:0.348:0.241. The research in this paper reveals the good effect of micropiles against landslides, explains the mechanism of pile–soil interaction, and provides a theoretical reference for the research and application of micropiles in engineering. [ABSTRACT FROM AUTHOR]

This study investigates the structural bearing capacity and deformation behaviors of micropiles considering various influence factors including the length (L) of micropiles, outer diameter (d) and wall thickness (t) of steel pipes, diameter (r) and spacing (s) of grouting holes, and water cement ratio (w/c) of grout. Multi-stage axial compressive tests were performed on 20 micropiles to obtain their deformation behavior and axial compressive loads respectively corresponding to the cracking of surrounding grout (Pcr), yielding of steel pipes (Py), and global structural failure (Pult). Experimental results reveal that Pcr and Py are respectively 0.20–0.45 and 0.85–0.95 times Pult. In general, Pult decreases with L. Increasing d produces a more significant improvement in Pult compared to increasing t. The influences of r and s on Pult are associated with the weakening of stiffness and strength of the steel pipes. Micropiles with various w/c levels perform similar Pult, whereas their axial displacement at Pult increases with w/c. Under the same L or w/c condition, increasing d leads to an obvious reduction in the axial displacement at Pult. In the existing criteria, the performance of prediction equations for Pult and allowable axial compression load (Pc) was compared and evaluated. Furthermore, several empirical models were proposed to respectively predict Pult and Pc of the micropiles considering the influences of L, d, t, r, s, and w/c and achieve well predictions. [ABSTRACT FROM AUTHOR]

An unstable slope is identical to the low value of their factor of safety (FS). Slope with low FS are in critical condition, which can cause landslides. On the other hand, the presence of triggering factor such as rain and human activities will increase the percentage of landslide. It has happened in Dompyong village. The Rocscience Slide Program, used to analyze slope stability in Dompyong village based on the simplified – bishop method. Based on the analysis, the FS value of the initial condition of slope is 0,85. Therefore, the slope is in critical condition because the FS value is less than 1,07. A combination method of retaining wall and micropiles is used to strengthen slope stability. This method can increase the FS value to 1,370. The slope is in a stable condition relatively because the FS value is more than 1,25.

IMPROVEMENT OF PIPELINE SETTLEMENT USING MICROPILESABSTRACTLoose sand soil is one of the problematic soils and according to that, buried pipelines interact with the loose sand soil. Also, pipelines are subjected to additional stresses transmitted by the settlement of the loose sand soil which increase stresses and displacements in the pipes and eventually leading to breakage. therefore, using micro - piles to improve soil below pipeline is important. Plaxis 3D numerical analysis software was used to investigate numerically the improvement of soil behavior below pipeline Micro-piles were installed as a cross piles configuration below pipeline and as a confining setup. Parameters studied are piles spacing, piles diameter, length and effect of water. Pipeline was subjected to surface loads from fully loaded truck. It was found that using micro-piles decreases considerably the settlement of pipelines resting on loose sands.Keywords: Loose Sand, Pipelines, Settlement, Improvement, Numerical Analysis, Plaxis 3D, Cross Piles, Confined Piles

This study summarizes the engineering design and calculation methods of micropiles and proposes a pile length optimization model based on numerical simulation software. Based on the proposed micropile calculation method and optimization method, a specific analysis of a project example was carried out, and a series of calculations, such as micropile design calculation and pile length optimization for the project, was completed. The results show that the miniature pile length optimization model based on numerical simulation finite difference method improves the previous method by automating the optimization process through fast modeling, automatic creation of optimization commands, and output and analysis of optimization results, and realizes the optimization of pile length using numerical simulation, which improves the efficiency of the optimization of the pile length under the premise of guaranteeing accuracy, and achieves the unity of both efficiency and accuracy. The feasibility of this optimization process is proved by engineering examples. The engineering practicability of the micropile design calculation method and optimization method proposed in this study is proved through practice. It provides a reference value for the initial fast and flexible management of small landslides.

A landslide occurred on November 24, 2019, in weathered phyllite at the western longwall of Yabaling open pit of Anqian iron mine in Anshan City, Liaoning Province, China. The landslide was estimated to be 3.0 × 104 m3 in volume and caused severe damage to the road of transporting waste materials. This landslide was a typical jointed rock mass landslide, and the cause of the landslide was related to four factors: open-pit mining activity, the weak rock, discontinuities, and the high rainfall. According to the failure characteristics, the landslide area was divided into three parts: the tension-cracking area, the sliding-deformation area, and the colluvium area. The failure mechanism of the landslide was investigated through a back analysis combining nonlinear Hoek–Brown criterion and FLAC3D program with a parameter reduction technique. The results showed that the predicted sliding surface at the critical state matched closely the field observations. A remedial scheme of landslide stabilization including four rows of micropiles was proposed and the stabilization mechanism of the micropiles was discussed. The shear strain increment contours show that the micropiles arrested the original sliding surface and controlled the movement of the sliding mass behind them, and thereby significantly improved the stability of the landslide. This paper also presents the results obtained from the parametric analysis in order to understand the impact of strength parameters on the long-term stability of the stabilized slope. The findings improved understanding of the failure characteristics and mechanism of jointed rock mass landslides may be used for evaluating the stability of slopes and early identification for both active and inactive open-pit mines. [ABSTRACT FROM AUTHOR]

Copyright of Ingeniería (0121-750X) is the property of Ingenieria and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There are various methods for reinforcing a railway track subgrade, but the greater challenge lies in improving an existing railway track in the least possible time with minimum disruption to rail traffic. Micropiles can provide an alternative solution for the improvement of existing railway tracks. The application of micropiles does not require blocking of rail traffic or dismantling of existing tracks. This study aims to evaluate the effectiveness of micropiles as a ground improvement technique for existing railway tracks. Micropiles were tested on two types of soil–clay and silt. A complete parametric study varying the geometrical configurations of micropiles was conducted using the FEM. Variation of micropile geometry in terms of, for example, diameter, length, spacing, and angle of inclination was also discussed. The results of FEM analysis were further utilized to train a genetic programming (GP) model. Empirical equations for the prediction of track displacement were drawn up using GP analysis; the behavior of tracks for different reinforcement conditions was also discussed. The resultant equations can also be effectively used for predicting track performance under given conditions. [ABSTRACT FROM AUTHOR]

Featured Application: The paper is useful for those who are interested in the seismic behavior of micropiles and micropiled structures; furthermore, it is presenting the concept of associating micropiles with seismic dampers and the idea of using micropiles to enhance the seismic behavior and resilience of structures (for new structures or to retrofit existing ones). The aim of this paper is to present the relevant information and development available in the scientific literature regarding the seismic behavior of micropiles (MPs) and micropiled structures (MPed). The seismic behavior of MPs is not very well studied, but MPs are used in retrofitting of old buildings and for new resilient buildings, and in terms of seismic behavior they have a high potential. Additionally, their association with seismic dampers for improving the seismic behavior of buildings is not yet fully studied and it represents a major topic of interest for both new structures and historical monuments. After the introductory part, the paper describes all relevant information regarding MPs, as types and technology, seismic behavior, applications for increasing seismic resilience, and experimental and numerical modeling. [ABSTRACT FROM AUTHOR]

Root piles are injected and installed during mortar shaft construction, using pressures of up to 500 kPa. The executive control is typically done through static load testing, an expensive and time-consuming method. Static load tests on eight controlled piles (diameters between 310 mm and 410 mm) were performed, aiming at evaluating pile ultimate load. This study suggests an innovative, non-destructive approach to validate root pile field performance, using a digital speedometer connected to the drilling rig’s rotating head. The proposed method monitors variables related to bearing capacity during pile installation and proposes an empirical equation to estimate the ultimate bearing capacity of root piles. For the assessed piles, the predictions obtained with the proposed equations agreed fairly well with results from static load tests, proving it as a feasible and helpful option for the executive control of root piles, especially when load tests are not available.

Root piles are injected and installed during mortar shaft construction, using pressures of up to 500 kPa. The executive control is typically done through static load testing, an expensive and time-consuming method. Static load tests on eight controlled piles (diameters between 310 mm and 410 mm) were performed, aiming at evaluating pile ultimate load. This study suggests an innovative, non-destructive approach to validate root pile field performance, using a digital speedometer connected to the drilling rig's rotating head. The proposed method monitors variables related to bearing capacity during pile installation and proposes an empirical equation to estimate the ultimate bearing capacity of root piles. For the assessed piles, the predictions obtained with the proposed equations agreed fairly well with results from static load tests, proving it as a feasible and helpful option for the executive control of root piles, especially when load tests are not available. [ABSTRACT FROM AUTHOR]

Micropiles can act as structural support for a new foundation and sustainable solution for existing foundations with advantages such as high load-carrying capacity and use in in situ conditions. Installing micropiles around the footing at some distance from the footing edge could turn out to be extremely helpful for existing distressed foundations where improvement is needed. An experimental investigation is carried out on a laboratory model square footing in the ongoing study, placed on sand, with micropiles driven around the footing. A parametric study focusing on the effect of the slenderness ratio of the micropiles, the state of sand beds, the micropile spacing ratio (S/b), and the micropile edge distance ratio (ED/d) are analyzed. The results demonstrate that the micropiles can appreciably improve the footing's settlement characteristics and load-bearing capacity when placed around it. The load-carrying capacity shows some appreciable increase by increasing the slenderness ratio of micropiles, but increasing the slenderness ratio beyond 20 is insignificant. For unreinforced footing, a denser form of sand was found more advantageous in terms of bearing capacity, while as for reinforced footing, micropiles provided maximum improvement for medium-density sand. The improvement in bearing capacity is approximately 22.2% when the spacing ratio is reduced from 0.5 to 0.3. Also, for an edge distance ratio of 3, the improvement in the bearing capacity ratio is 76% higher than that of unreinforced footing. Multivariate linear regression showed a strong correlation between the experimental and predicted bearing capacity ratio. [ABSTRACT FROM AUTHOR]

So far insufficient research has been done on the long-term behavior of micropiles embedded in a clay medium, even though this has a significant influence on the expected total settlement. This paper considers a square foundation placed on a clay bed and tested under vertical loads until the clay reached its bearing capacity. Subsequently, the plate was underpinned with four micropiles, and the load test was repeated. These test data were used to validate the coupled hydraulic-mechanical three-dimensional finite difference model presented in this paper. In the numerical modelling, four different load transfer scenarios were considered to simulate different approaches to adding floors to an existing building. Consolidation periods of zero months, six months, and five years between the application of the load due to the existing building, and the application of loads due to additional storeys were considered. The six-month period represents a short-term, and the five-year period a long-term scenario. Following the first consolidation period and the application of loads representing additional storeys, a second consolidation period was implemented, such that the combined length of the two consolidation periods was five years. In this study, the results showed that the installation of micropiles immediately after the completion of existing floors is most successful in controlling the settlement of additional floors later on.

Digging tunnels in areas of low strength often leads to a decompression of the face, which can lead to significant ground movements as well as to face failure. Thus, tunneling through a soft ground, with a thin soil cover, where the ground arch effect is not effective enough, can be catastrophic for the construction site personnel. The objective of this paper is to examine the influence of frontal bolting and vertical reinforcement on the behavior of the massif in a section of the T4 tunnel in Algeria. The modeling consists on the one hand in considering a simplified approach for the reinforcement of the core-face and on the other hand in establishing micropiles as vertical reinforcement in the shallow overburden zone. The analysis of the results of this work showed that face bolting can result in an improvement in face stability and a decrease in face deformation. It also showed that the micropiles pre-reinforcement technique may also be necessary to generate an arc effect, an essential condition for the short- and long-term stability of shallow tunnels. [ABSTRACT FROM AUTHOR]

In this study, a large-scale model test was performed to investigate the effect of the single-row and double-row micropiles on the landside stabilization. For two different testing configuration settings, the bending moment along the micropiles, failure mode, and force condition were captured and compared. It is found that the landslide thrust on piles was distributed in a triangular shape. The piles in the front row carried greater pressure than the piles in the rear row. The resistance of the sliding body behind the pile was distributed in a parabolic shape, and mainly concentrated on the middle of the pile. The piles were destroyed due to the combined shearing and bending impact applied near the slipping surface. The boundary of the failure zone was from the position of two times the pile diameter under the slipping surface to the position of two and a half times the pile diameter above the slipping surface. Under the action of the landslide, each row of piles deformed at the same time. The capability of landslide stabilization for double-row piles was better than that of a single-row pile. The sections of the pile above slide surface were mainly subjected to negative bending moments and were distributed mainly within the pile length range of one-third of the anti-sliding section above the sliding surface. The pile body of the embedded section located in the range of ten times the pile diameter below the sliding surface was subjected to a positive bending moment.

Featured Application: This paper investigated the reinforcement and stabilization effects of micropile on slopes by carrying out static and dynamic model tests. Through systematic research and comparison, the reinforcing mechanism, seismic response mechanism, and failure modes of the micropiles are discussed to provide a more reliable basis for the micropile design in landslide prevention and slope stabilization design. To study the static and dynamic response of micropile-reinforced slopes, static model tests and shaking table tests were performed. The failure modes, the pile-slope interaction, the displacement, and the static/dynamic earth pressure distributions were analyzed based on static and dynamic model tests with a prescribed sliding surface. The test results indicated: (1) The micropile failure mode is mainly bending failure under both loading conditions. As far as the damage to the pile body is concerned, under static loading, the rear row piles showed more damage than the middle row piles followed by the front row piles. Under dynamic loading, the damage of the rear row piles was approximately the same as the middle row piles, which was greater than the front row piles; (2) The earth pressures in front of and behind each row of micropiles and the axial force of the pile body distributed triangularly for both loading conditions, with the bending moment of the pile body distributed in an "S" shape; (3) The landslide thrust experienced by the micropiles has a relatively large group effect. The group effect or shear ratio parameters are recommended for each loading case; (4) The interaction between the micropiles and the soil landslide presents evident progressive failure and load transfer between the rows. [ABSTRACT FROM AUTHOR]

In this study, the axial and lateral load-carrying behavior of encased micropile (MP) with perforated configuration was investigated. The perforated casing adopted in this study was a casing with holes on the casing surface to increase the frictional and bending resistances. Experimental tests and finite-element (FE) analyses were performed to characterize the interface friction and the effect of the perforated casing, considering the inclined condition of MP. The experimental tests showed that the interface friction angle of the perforated casing was close to the sand friction angle, whereas that of the smooth-surface casing was nearly half of the sand friction angle. The frictional characteristics of the smooth and perforated casings obtained from the experimental tests were used in the FE analysis. The perforated casing was sufficiently effective to maintain the reinforcing effect of the casing on the lateral load capacity. The axial load capacity of MP with the perforated casing was 22.4% higher than that with the conventional smooth casing. A similar improvement was observed for inclined MPs. It was indicated that the perforated casing was beneficial for both axial and lateral loading capacities. [ABSTRACT FROM AUTHOR]

In this paper, the lateral load-carrying behavior of inclined micropiles installed in various soil–rock layer conditions was investigated based on the results from the model load tests and finite-element analyses. The effects of micropile inclination angle, load direction, and rock-embedded ratio were considered in the study. Improved load-carrying behavior was obtained from negatively inclined micropiles in rock with the load direction of 0°, whereas it was disadvantageous for the load directions of 90° and 180°. The lateral load capacity of micropiles for the mixed layer condition increased with a rock-embedded ratio and became larger at a higher inclination angle. Marked increases in the lateral load capacity were observed for rock-embedded ratios larger than 0.8, below which the increases were moderate. The inclination and rock-embedded conditions of micropiles were both adequate to enhance the lateral load-carrying behavior of micropiles, whereas the effect of the rock-embedded condition was less beneficial unless largely embedded. It was also indicated that the maximum benefit of micropiles embedded in rock could be achieved by further reinforcing the stiffness in the upper part of micropiles within the soil layer. It was confirmed that the previously proposed method to estimate the lateral load capacity of inclined micropiles in the sand could be effectively used for the case in rock and the mixed soil–rock layer condition for practical purposes. [ABSTRACT FROM AUTHOR]

A series of shaking table tests were conducted on unreinforced and micropiles-reinforced soil landslides to investigate the seismic response of micropiles-reinforced landslide and the dynamic mechanical behaviour of micropiles in landslide under earthquake. The test results indicate that: (1) The micropiles can raise the anti-seismic performance of landslide, and it can efficiently delay the development of earthquake landslide hazards. (2) After earthquake, the flexural failure of micropile mainly occurs in the area that 1.4–4 times pile diameter above the sliding surface and the area that 1.4–3.4 times pile diameter below the sliding surface. (3) After reinforced by micropiles, the acceleration response on the slope surface of landslide can be decreased, especially the slope toe. (4) Both thrust of sliding mass and resistance of sliding bed are mainly concentrated near the sliding surface. The dynamic bending moment distributions of the three rows of micropiles present as reverse ‘S’. The maximum bending moment of the pile above sliding surface is located at the point that 3.7 times pile diameter above sliding surface, and the maximum bending moment of the pile below sliding surface is located to the point that 1.43 times pile diameter below sliding surface.

The main objective of the present paper is the application of a design method, traditionally used for medium- and large-diameter piles, to nongrouted hollow steel bar micropiles with very small diameters. The compressive resistance of this piling system, which is generally used for underpinning works, can be controlled during installation. The adopted analytical design method is based on the results of cone penetration tests to calculate the resistance of the micropiles under compression. Thanks to the availability of field data from micropiles installed at different sites, it was possible to fit the analytical method and to compute the characteristic value of micropile resistance. A Monte Carlo analysis has been used to test the reliability of the method and determine the reduction correlation factor for the calculation of the characteristic resistance. The obtained results show how the analytical method can be effectively adopted for micropiles installed in prevalently coarse-grained soils. An appropriate value of the correlation factor that fulfills the reliability requirements has been derived. On the one hand, this correlation factor is only slightly lower than that prescribed by European regulations (Eurocode 7); on the other hand, it appears much less conservative than that prescribed by the Italian Code. The adopted statistical approach appears rather promising to develop appropriate design methods for similar micropile systems in different soils. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present the relevant information and development available in the scientific literature regarding the seismic behavior of micropiles (MPs) and micropiled structures (MPed). The seismic behavior of MPs is not very well studied, but MPs are used in retrofitting of old buildings and for new resilient buildings, and in terms of seismic behavior they have a high potential. Additionally, their association with seismic dampers for improving the seismic behavior of buildings is not yet fully studied and it represents a major topic of interest for both new structures and historical monuments. After the introductory part, the paper describes all relevant information regarding MPs, as types and technology, seismic behavior, applications for increasing seismic resilience, and experimental and numerical modeling.