Coupled nonlinear thermo-hydro-mechanical finite element simulations were carried out to investigate the behavior of energy micropiles subjected to thermal loading cycles. Two kinds of problems were analyzed: The case of an isolated micropile, for which comparison with previous research on medium-size isolated energy pile is provided, and the case of large groups of micropiles, with the aim of investigating the interaction effects. In both problems, micropiles were considered installed in a thick layer of very soft, saturated clay, characterized by isotropic or anisotropic hydraulic conductivity. Two advanced existing hypoplastic models, one incorporating the thermal softening feature, were used to describe the clay behavior in both problems. The settlements of the micropile head were found to increase during thermal cycles under constant mechanical load, showing a sort of ratcheting. For micropile groups, the settlement increase rate was faster as the spacing between micropiles was reduced. The excess pore water pressures developed at the micropile-soil interface played a significant role on the deformation and displacement fields of the soil-micropile systems, especially in the case of micropile groups, affecting the shear strength developed at the micropile-soil interface. The consolidation process was faster when the hydraulic conductivity was anisotropic, meaning that the development of excess pore water pressure was reduced in this case. As the spacing between the micropiles increased, i.e., as thermal interaction decreased, the heat flux exchanged by a micropile of the group during one cycle approached the heat flux exchanged by an isolated micropile in the same period.

This study presents a novel investigation into the seismic response of micropiles through shaking table tests, diverging from the predominant reliance on numerical analyses in assessing micropiles in liquefiable sites. Three models of shaking table tests were conducted using Iai scaling rules for physical modelling in 1-g conditions. The investigation reveals a significant dependency of micropile efficiency on the frequency of input motions. During the 2 Hz test, the entire model experienced liquefaction; however, in the 3 Hz test, there was a remarkable 29% reduction in excess pore water pressure. Additionally, the study explores the impacts of varying distances between micropiles and examines how liquefaction influences the induced peak accelerations at different depths within the soil media. Notably, recorded accelerations on the surface decreased by up to 76% in the free field tests during liquefaction. This comprehensive exploration advances our understanding of micropile behaviour under seismic conditions, offering valuable insights for soil improvement projects.

In order to study the force characteristics and reinforcement mechanisms of the bank protection capacity of micropile groups under rain seepage, two different scale models were employed using model tests and the finite element method. Focusing on the stress within the micro-piles, the lateral soil pressure against the piles, the displacement at the pile tops, and the overall stability of the embankment reinforced by the micro-piles, engineers can assess the performance and durability of the structure during rainwater scouring. The study shows that rainfall leads to increased soil saturation, which in turn reduces the soil's shear strength. When subjected to loading after rain, micropiles within the same row exhibit similar strains. The thrust from potential landslides at the top of the slope causes the rear row of piles to experience greater flexural deformation. The difference between the soil pressure values of the same row after rainwater infiltration is small, and the overall soil pressure value increases in a stepwise manner with the increase of loading volume. The micropile support helps reduce soil displacement. The displacement of the middle and front row of piles is significantly lower compared with the back row by 32.3 % and 35.7 %, respectively. The pile group can limit the soil displacement within a certain range, which is beneficial for improving the stability of bank slopes under rainfall scouring. The micropile group enhances the overall slip resistance of the bank slope and can inhibit the development of the slip and crack surface of the bank slope to a certain extent. In engineering design, it is crucial to determine an appropriate pile spacing. A too small spacing can prevent the piles from achieving their optimal bending strength, whereas too large a spacing may lead to the risk of the bank slope as a whole experiencing overturning damage.

Soil-rock interface landslides are common geological hazards in mountainous regions. While conventional cement-based micropiles are widely used for slope stabilization, their long curing time limits their application in emergency treatments. This study introduces polymer micropiles as a rapid-response alternative, leveraging the quick-setting and high tensile strength properties of polymer grouts. Field-scale tests and numerical simulations were performed to investigate the mechanical response and settlement deformation characteristics of the bedding slopes reinforced with polymer micropiles under loading. Results showed that polymer micropiles significantly improved slope bearing capacity, reduced crest settlement, and decreased surface displacement. Specifically, the bearing capacity of slopes reinforced with single and double rows of polymer micropiles increased by 111% and 211%, respectively, compared to the unreinforced slope. Settlement at the slope crest decreased by 76.9% and 90.4%, while lateral displacement at the slope toe was reduced by 77.8% and 92.8%. The final slope morphologies showed significant differences, with pronounced extrusion and soil detachment observed in the untreated slope, contrasted by only minor surface cracks in the polymer micropile reinforced slope. The simulations revealed that the micropiles fractured at the sliding plane when reaching the ultimate bearing capacity, indicating the compatibility of polymer micropile with the slope soils and the reinforcing effect of the micropiles. These findings demonstrate the feasibility and effectiveness of polymer micropiles for emergency landslide stabilization, offering a critical window for disaster response and permanent slope stabilization efforts.

The practical application of micropiles in landslide reinforcement and prevention advanced before theoretical research, significantly limiting their application and promotion. To determine the damage patterns and stress distribution of micropiles during sliding failure in reinforced shallow landslides, three sets of physical modeling tests were performed. These tests examined the stability of shallow soil slopes with and without micropiles, including single-row and three-row configurations. During the tests, the foot displacement of the landslide, the top displacement of the micropiles, and the strain within the micropiles were monitored throughout the loading process. Following the tests, the landslide was excavated to observe the damage patterns in the micropiles. The experimental results showed that the pile-soil composite structure formed by three rows of micropiles, together with the soil between them, significantly improved the stability of the landslide and demonstrated effective anti-sliding effects. The stress distribution curve of the micropile was inversely S-shaped, with the peak stress located near the sliding surface. Within the micropile group, the first row exhibited the highest stress, and the micropiles nearest to the free face experienced the greatest displacement. Through the micropile-reinforced landslide tests, we identified three stages in the slope's sliding damage process and the stress distribution pattern of the micropiles. The research findings offer valuable insights into the anti-sliding mechanism of micropiles, which can guide design and construction.

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 x 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 degrees, 5 degrees, and 10 degrees 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.

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.

The use of a micropile group is an effective method for small and medium-sized slope management. However, there is limited research on the pile-soil interaction mechanism of micropile groups. Based on transparent soil and PIV technology, a test platform for the lateral load testing of slopes was constructed, and eight groups of transparent soil slope model experiments were performed. The changes in soil pressure and pile top displacement at the top of the piles during lateral loading were obtained. We scanned and photographed the slope, and obtained the deformation characteristics of the soil interior based on particle image velocimetry. A three-dimensional reconstruction program was developed to generate the displacement isosurface behind the pile. The impacts of various arrangement patterns and connecting beams on the deformation attributes and pile-soil interaction mechanism were explored, and the pile-soil interaction model of group piles was summarized. The results show that the front piles in a staggered arrangement bore more lateral thrust, and the distribution of soil pressure on each row of piles was more uniform. The connecting beams enhanced the overall stiffness of the pile group, reduced pile displacement, facilitated coordinated deformation of the pile group, and enhanced the anti-sliding effect of the pile-soil composite structure.