This study investigates the influence of wood pellet fly ash blended binder (WABB) on the mechanical properties of typical weathered granite soils (WS) under a field and laboratory tests. WABB, composed of 50 % wood pellet fly ash (WA), 30 % ground granulated blast furnace slag (GGBS), and 20% cement by dry mass, was applied at dosages of 200-400 kg/m3 to four soil columns were constructed at a field site deposited with WS. After 28 days, field tests, including coring, standard penetration tests (SPT), and permeability tests, revealed enhanced soil cementation and reduced permeability, indicating a denser soil matrix. Unconfined compressive tests (UCT) and free-free resonant column (FFRC) tests on field cores at 28 and 56 days, compared with laboratory specimens and previously published data, demonstrated strength gains 1.2-2.1 times higher due to field-induced stress. The presence of clay minerals influenced the WABB's interaction and microstructure development. Correlations between seismic waves, small-strain moduli, and strength were developed to monitor in-situ static and dynamic stiffness gain of WABB-stabilized weathered granite soils.

The effect of the load level on long-term thermally induced pile displacements and the impact of cyclic thermal loads on the bearing capacity of energy piles are investigated via a full-scale in situ test in Delft, The Netherlands. The pile was loaded to a specific target of 0, 30, 40, or 60% of its calculated ultimate bearing capacity. At the end of each loading step, up to ten cooling-natural heating cycles were applied. The pile behavior during monotonic cooling and cyclic cooling-natural heating in terms of the displacement along the pile is reported, with a focus on permanent displacements. During monotonic (pile/ground) cooling, a settlement of the pile head and an uplift of the pile segment near the pile tip were observed in all four tests. In addition, under higher mechanical load, the pile head displacement was larger while the uplift was lower due to the imposed mechanical load. During cyclic thermal load, under zero mechanical load, pile head displacement was fully reversible while permanent uplift of the lowest pile segment was observed and attributed mainly to the permanent dragdown of the surrounding soil. Under moderate mechanical loads (30 and 40%), thermal cycles induced an irreversible pile head settlement, which stabilized with an increasing number of cycles. In addition, a permanent pile settlement along the pile was observed at the end of these tests. Under high mechanical load (60%), the irreversible settlement along the pile continued to increase with only a slight reduction in rate, being higher compared to moderate mechanical loads. In this test, a normalized pile head settlement of 0.124% was observed after ten thermal cycles. The permanent settlement of the pile under thermo-mechanical loads was mainly attributed to the contraction of sand beneath the pile tip and thermal creep at the soil-structure interface. The pile bearing capacity was observed to increase after thermo-mechanical tests, mainly due to the residual/plastic pile head displacement, which in turn densified sand leading to an increase in tip resistance.

Numerous full-scale in situ tests have been conducted to assess the effect of thermal cycles on the pile response. However, those studies investigated the response of only precast and cast in-situ energy piles, with limited focus on the impact of the applied mechanical load on the pile response. This study presents the results of a field test conducted on a new type of energy pile, i.e. a displacement cast in-situ energy pile in multilayered soft soils, subjected to different fixed mechanical loads while undergoing simultaneous thermal cycles. Four tests were carried out, each corresponding to various axial loads ranging from 0 % to 60 % of the pile's estimated bearing capacity. After applying the axial load on the pile head (0 %, 30 %, 40 %, or 60 % of the bearing capacity), the pile was subjected to up to ten thermal cycles. The highest magnitudes of thermal axial strains were observed near the pile top due to the lowest restraint provided by the made ground layer in all tests. Under zero (0 %) mechanical load, the thermal axial strains near the pile head were elastic and recoverable, while residual strain was observed near the toe. Under reasonable working mechanical loads (30 %, 40 %, or 60 %) residual strains were observed near both the pile head and the toe, with higher residual strains observed under higher mechanical loads. The results indicate that the cyclic thermal loadings could induce an increase in the compressive stress in the energy pile, attributed to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects counteracts thermally induced tensile stress and thus leads to an insignificant effect on the energy pile during cooling. A limited impact of the shaft capacity was observed and was mainly attributed to the drag-down of the surrounding soil and thermal creep along the pile-soil interface.

The PHC (pre-stressed high-strength concrete) pile foundation, serving as an innovative supporting structure for solar power stations, is subjected to complex loading conditions in engineering scenarios. In this study, field tests of the full-scale PHC Pile foundation were conducted in sand layer, loess layer, and double-layer sites to investigate its operational behavior under different load conditions. The study assessed the inclination of the column top, ground displacement, and torsion to analyze the stress and deformation characteristics of PHC pile foundations. The deformation of PHC short pile foundations exhibited distinct phases. Torsional load reduced the column crack load by 30%. The pile cap effectively controlled plastic deformation, minimizing foundation deformation, while torsional load increased lateral deformation. Under cyclic load, the PHC pile behaved with an approximate elasticity characteristic within the test load range. The deformation increased by approximately 10%. Furthermore, three-dimensional numerical simulations analyzed the effects of foundation dimension, bending-moment-to-lateral-load ratio, torque-to-lateral-load ratio, and pile cap size on internal forces and deformation. Simulations indicated that increasing the pile cap length was more advantageous for reducing deformation and internal forces. The bending-moment-to-lateral-load ratio was significant in design, while the torque-to-lateral-load ratio had a negligible impact. A comprehensive design program is proposed based on field tests and numerical simulations, considering deformation and bearing capacity. The study confirms the reliability of the PHC pile foundation as a support structure for heliostats, aiming to offer valuable insights for practical applications.

Examples of upscaling phenomena with experimental techniques are presented and discussed within the framework of compacted soils for hydraulic and environmental earthworks and engineered barriers for the energy sector. A series of laboratory experiments at different scales are presented and interpreted to focus on the need for experimental upscaling in compacted soils since distinctive behavioural features can only be detected at specific length scales. Permeability results on fine-grained soils and artificially prepared sand/bentonite mixture at different scales will be discussed with microstructural tests regarding 'dry' or 'wet side' compaction, element and mock-up tests on compacted soils in the laboratory, and field tests on a compacted trial embankment and demonstration test to explore anisotropic and heterogeneous features. The presented examples will help to motivate new experimental research subjects and promote experimental protocols at different scales ranging from mm-scale (micro), cm-scale element tests, dm-scale mock-ups and m-scale (trial/demonstration tests) to help understand and approach some fundamental questions observed at the application scale of compacted soils.

The construction of fill slopes becomes a critical aspect when there is a need to change the terrain or create new terrain. However, due to the poor engineering properties of the fill material, especially when red sandstone with notable disintegration properties is used, the risk of slippage or collapse may occur. This material is prone to erosion and disintegration under the action of natural factors such as heavy rainfall, leading to severe soil erosion and slope instability. In addition, the construction of fill slopes inevitably causes the destruction of native vegetation, exacerbating environmental problems. To address these problems, an novel ecological approach for preventing water damage to red sandstone fill slopes was developed using the vegetation-high-performance turf reinforcement mat -anchor-drainage pipe-synergistic slope protection system. Three test red sandstone slopes with different protection methods (unprotected, three-dimensional (3D) protection mesh, and vegetation ecological protection system slopes) were constructed, and the feasibility and reliability of ecological protection against water damage to red sandstone fill slopes were analysed via the field test method. The results showed that the vegetation ecological protection system can effectively inhibit soil erosion and increase the survival rate of vegetation roots. Moreover, the the high-performance turf reinforcement mat provides a strong protective complex through interactions with vegetation roots, anchors, and drains, which significantly enhances slope stability. Under heavy rainfall conditions, the vegetation ecological protection system can effectively limit slope erosion due to water scour, thus maintaining the structural integrity of the slope.

The alkali-activated composites technique is a promising method for the in situ preparation of cavity filling/grouting materials from engineering waste soil. To investigate the feasibility of engineering waste soil utilization by the alkali activation process, the macroscopic and microscopic properties of the fly ash/slag-based alkali-activated composites, after solidification/stabilization (S/S) with sandy clay excavated at Baishitang Station of Shenzhen Metro, were studied. The unconfined compressive strength (UCS) test was conducted to evaluate the S/S effect of alkali-activated composites. The results show that the optimum quality ratio of slag and fly ash correspond to 7:3, the modulus of alkaline activator to 1.3, and the alkalinity of alkaline activator to 10%. The alkali-activated composite's strength under these parameters can reach 45.25 MPa at 3 days, 49.85 MPa at 7 days, and 62.33 MPa at 28 days. A maximum 3-day UCS of 21.71 MPa, 75% of the 28-day UCS, was achieved by an engineering waste soil and alkali-activated composites mass ratio of 5:5, slaked lime content of 4.5%, and a water-to-solid ratio of 0.26, and it can also meet the required fluidity and setting time for construction well. Fluidity is primarily affected by the soil-to-binder ratio, which decreases as the ratio decreases, while the water-to-solid ratio increases fluidity. Slaked lime has minimal impact on fluidity. The setting time is mainly influenced by the soil-to-binder ratio, followed by slaked lime content and water-to-solid ratio, with setting time shortening as the soil-to-binder ratio and slaked lime content increase, and lengthening as the water-to-solid ratio increases. Through Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) tests, microscopic analysis showed that loose granular units are firmly cemented by alkali-activated composites. Based on the results of on-site grouting tests in karst caves, the alkali-activated grout materials reached a strength of 5.2 MPa 28 days after filling, which is 162.5% of the strength of cement grouting material, satisfying most of the requirements for cavity filling in Shenzhen.

To broaden the sources of subgrade filler and the utilization of Soda Residue (SR), SR was employed to modify clay by adding a small amount of lime for further stabilization, forming a Lime-Soda-Residue-Stabilized Soil (LSRSS). A set of intensive research paths was established, from testing of laboratory mechanical property, mechanism disclosure, and field verification to operational effect. Through Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and Resilient Modulus (MR) experiments, it was concluded that with the increase in SR content, the UCS, CBR, and MR values of LSRSS showed an increasing trend then followed by a decrease, reaching their peak values, respectively of 0.62 MPa, 65.0%, 78.83 MPa, all at 30% SR content. An optimal proportion was determined for LSRSS as 6% lime, 30% SR, and 70% clay. The UCS, CBR, and MR values of optimal proportion all increased with the increase of compaction degree, but increased first and then decreased with the increase of water content. Their maximum values did not correspond to the OWC of 23% but to 27%, called the compaction water content, which was suitable for application in the actual LSRSS subgrade. Field test results showed that the UCS, CBR, and MR values were 0.85 MPa, 86.5%, and 135.7 MPa, which all were higher than the laboratory values, and the long-term road performance was outstanding. The analysis demonstrates that the better strength and road performance of LSRSS are mainly determined by the superior gradation and the reaction of three materials. The laboratory and field test results collectively provide data evidence for excellent performance and lay a solid foundation for the wider application of the LSRSS subgrade.