The studied earth dam was remediated works for seepage and instability problems in the downstream area. The effectiveness of slurry cutoff walls was investigated on seepage behavior. The three-dimensional (3-D) finite element (FEM) analysis at normal high-water level (NHWL) for steady-state flow was established without and with a cutoff wall. Based on the results, the overall effectiveness of the cutoff wall was 85%, which exceeded the predicted design efficiency criterion of 75%. The embankment, residual soil, and phyllite were the three major materials that mainly intercepted by cutoff wall, with decreasing flows of 72-89%, 85-94%, and 55-94% respectively. The phyllite and quarzitic schist below cutoff wall coverage, the flows increased by 179% and 33-61%. Thus, extension of the cutoff lower tip to cover the full depth through phyllite and into the quarzitic schist is highly recommended. The cutoff wall effectiveness reduced potential wet areas on downstream area by 97%, indicating lower risk of seepage erosion. Major reductions in the phreatic line drop were observed of 12-20 m, indicated the hydraulic gradient across the wall thickness of 2.00-3.33 which are less than 4.00 against wall blowout. The piezometric heads of the existing field monitoring are higher than the model without the cutoff wall indicated the possibility of internal erosion. However, this would be clearly solved after cutoff wall construction. The estimated newly installed piezometer heads across the cutoff wall are planned. The model estimates the heads from dam axis to downstream area would lower from 160 to 140-145 m Mean Sea Level (MSL). That would certainly increase the safety on seepage and stability of the downstream slope.
Stone columns are widely used to improve soft ground, and their mechanical behavior is commonly represented by homogenized composite assumptions at the unit-cell level. However, such assumptions are often adopted without sufficient large-scale experimental validation and may not adequately capture the nonuniform load transfer, confinement-dependent friction mobilization, and drainage-sensitive nonlinear response caused by the interaction between a granular column and the surrounding soft clay. To address this issue, a series of large-scale triaxial tests was conducted on stone column-reinforced composite unit cells under static loading. The effects of area replacement ratio, confining pressure, and drainage condition on the stress-strain behavior, peak deviatoric stress, and equivalent shear strength parameters were systematically examined. Based on the test results, a modified Duncan-Chang hyperbolic model was developed, in which the area replacement ratio was explicitly incorporated into the constitutive parameters through experimental calibration. The results show that both the soft soil and the composite unit exhibit strain-hardening behavior, while the reinforced composite develops higher stiffness and strength. The peak deviatoric stress increases approximately linearly with confining pressure and replacement ratio. In addition, the equivalent cohesion changes only slightly after reinforcement, whereas the equivalent friction angle increases significantly, indicating that the strengthening effect is governed mainly by frictional enhancement. The modified model reproduces the measured stress-strain curves with good accuracy, with coefficients of determination generally above 0.90 and relative errors in peak deviatoric stress within about 10% for the tested cases. The proposed framework provides a practical constitutive description for stone column composite unit cells and a useful basis for geotechnical analysis and design.
Grouting is an essential technique for managing settlement and rectifying uneven subsidence in construction. Despite its significance, determining grouting parameters primarily relies on empirical experience, resulting in a lack of systematic and scientifically grounded methodologies. Thus, it is crucial to utilize numerical calculation methods to evaluate the effectiveness of grouting under various conditions. The calculation outcomes indicate that the formation pressure and grouting duration are critical factors that influence the expansion of the grout material. Notably, the relationship between formation pressure and the extent of grouting reinforcement displays an exponential pattern while it is inversely proportional to the reinforcement range. Building upon these analytical results, a comprehensive design framework for grouting schemes is proposed to enhance the uniformity and effectiveness of the grouting intervention. This approach optimizes the grouting process and contributes to the built environment's overall stability and structural integrity.
This study systematically investigates the compressibility of dredged clay with high water content using Portland cement (PC) and sodium silicate (SS) as composite stabilizers. The effects of SS content (0%, 3%, 6%, 12%) and curing time (3 hours, 7 days, 28 days) on compression behavior of PC-SS-stabilized specimens with the same PC content of 10% were investigated via one-dimensional consolidation tests, with microstructural evolution analyzed using SEM. Results show that PC-SS-stabilized soil exhibits significantly reduced compressibility compared to untreated soil. The e-lgp curve became bilinear, with a yield stress (p(y)) as the turning point, compressibility was low beforepy and increased markedly after. Compression indices (C-e, C-c) of stabilized soil were lower than those of untreated soil, initially decreasing and then increasing with SS content, reaching minima at 6%. The swelling index (C-s) was also the smallest at this content. Yield stress increased rapidly, then slightly decreased with SS addition, peaking at 6%. Longer curing time increased yield stress, most notably within 7 days, reduced porosity, and decreased compressibility. After 28 days, compression curves shifted upward. Microstructural analysis indicated that at 6% SS and 10% cement, continuous cementitious products formed, filling pores and cementing particles, thereby enhancing compressive performance.
Underground power distribution cables are typically installed using multi-conduit systems, in which the minimum spacing between adjacent conduits is prescribed primarily for electrical and thermal safety. However, such considerations are less critical for medium-voltage distribution systems and do not reflect the geotechnical behavior of closely buried conduits. This study presents a full-scale laboratory investigation to evaluate how conduit spacing affects soil-structure interaction and mechanical response under static and repetitive loading. Two configurations, a conventional spaced arrangement and a non-spaced arrangement, are constructed in a large instrumented soil chamber. Miniature cone penetration tests are conducted prior to loading to verify that the prepared backfill satisfied the target compaction level. Measurements of vertical soil pressure and conduit deformation reveal clear behavioral differences between the two configurations. The non-spaced configuration shows stress redistribution behavior consistent with the formation of a continuous arching mechanism, which is associated with reduced deformation under both static and cyclic loading. In contrast, the spaced configuration develops localized arching above individual conduits and exhibited greater deformation accumulation during repetitive loading. Supplemental uniaxial compression testing confirms that the stress levels mobilized in the full-scale experiments remain well within the elastic range of the polyethylene conduit, indicating minimal risk of structural yielding regardless of spacing. Overall, the results indicate that eliminating spacing does not compromise structural safety and produces favorable stress redistribution and deformation responses under the tested installation conditions. These findings suggest the need for further geotechnical evaluation of configuration requirements in medium-voltage distribution conduits.
