Experimental Study on Stiffness Softening of Soil-Rock Mixture Backfill under Metro Train Cyclic Load

Due to the thick soil layer, short backfill time, and low degree of consolidation of the soil-rock mixture backfill in Chongqing city, metro train tunnels passing through this type of strata are prone to large settlements during operation, which greatly affects the stability of the tunnel and the safety of metro train operations. In response to this problem, the dynamic triaxial test of the soil-rock mixture backfill under cyclic loading was carried out to study the dynamic characteristics of the soil-rock mixture backfill under cyclic loading. The effect of initial consolidation degree, effective consolidation confining pressure, and rock content on the stiffness softening of soil-rock mixture backfill was analyzed. The results show that the initial consolidation degree, effective consolidation confining pressure, and rock content are all important factors affecting the stiffness of soil-rock mixture backfill under cyclic loading. As the number of cycles increases, the lower the initial consolidation degree and effective consolidation confining pressure, the faster the attenuation of the softening index, and the larger the amplitude. As the rock content increases, the softening index increases and the stiffness of the backfill changes from softening to hardening. Based on the test data, the softening-hardening model of the soil-rock mixture is established, which is in good agreement with the field test results. This study can provide a reference for predicting and controlling the postconstruction settlement of the metro tunnel in the soil-rock mixture backfill.

Metakaolin Addition to Improve Geopolymerization Process and Properties of Waste Clay-Based Materials

The exploitation of different kind of clayey waste (halloysitic, smectitic/illitic, kaolinitic) for the production of geopolymers in the view of a circular economy of mines is the main goal of this study. In particular, the addition of low percentages of metakaolin (5-15%) was evaluated to improve the chemical-physical properties and the consolidation degree of geopolymeric formulations produced with clays classified as mine’s by-products. In fact, these secondary raw materials are often not sufficient alone to obtain chemically stable formulations with acceptable mechanical properties but require the addition of reactive fillers. All samples contained thermally treated clays (600°C-700°C) and metakaolin as aluminosilicate precursors, alkaline solution of NaOH and Na2SiO3, and were cured at room temperature. The influence on the final products with MK addition was monitored with the evaluation of the chemical stability in water (pH and ionic conductivity measures), the comparison of setting times (Vicat needle) and mechanical performance.

One-Dimensional Nonlinear Consolidation Analysis Using Hansbo’s Flow Model and Rebound-Recompression Characteristics of Soil under Cyclic Loading

Hansbo’s flow model for one-dimensional consolidation analysis of saturated clay has been widely recognized as being the most representative for soft soils. Many studies have used the model to examine the characteristics of soil under various conditions. However, very few studies have considered soil under cyclic loading. In this study, using a Hansbo’s flow model and assuming known characteristics for soft clay deformation and rebound and recompression of soil, the one-dimensional consolidation model of soft clay under cyclic loading is established. A FlexPDE solution scheme with excess pore pressure u and void ratio e as variables is also given. The reliability of the proposed method is verified by comparing the obtained results with existing results. On this basis, the consolidation characteristics of soft clay foundations under unilateral drainage and cyclic loading are studied. The effects of soil rebound and recompression characteristics, Hansbo’s flow parameters, cyclic loading period, and cyclic loading form on the consolidation characteristics of soft clay foundation are analyzed. The results show that under cyclic loading, the effective stress, void ratio, and average consolidation degree of the foundation all present a cyclic state and gradually enter a stable cyclic state with the increase in cycles. The peak of effective stress lags behind the peak of cyclic load. The rebound and recompression characteristics of soil have little effect on the effective stress of soil but a great effect on the void ratio. In contrast to its characteristic under linear loading, the average consolidation degree of the foundation under cyclic loading finally enters a stable cyclic state. The results of the analysis can be used as a reference in the analysis of real life highways, railways, subway tunnels built on soft soil foundations subjected to periodic cyclic loading.

Tracking Deformation Processes at the Legnica Glogow Copper District (Poland) by Satellite InSAR—II: Żelazny Most Tailings Dam

The failures of tailings dams have a major negative impact on the economy, surrounding properties, and people’s lives, and therefore the monitoring of these facilities is crucial to mitigate the risk of failure, but this can be challenging due to their size and inaccessibility. In this work, the deformation processes at Żelazny Most tailings dam (Poland) were analyzed using satellite Ad-vanced Differential SAR Interferometry (A-DInSAR) from October 2014 to April 2019, showing that the dam is affected by both settlements (with a maximum rate of 30 mm/yr), and horizontal sliding in radial direction with respect to the ponds. The load of the tailings is pushing the dam forward along the glacio-tectonic shear planes located at depth, in the Pliocene clays, causing horizontal displacements at a rate up to 30 mm/yr, which could lead to a passive failure of the dam. The measured displacements have been compared with the ones observed by in situ data from the 90s to 2013, available in the literature. The outcomes indicate that intense localized deformations occur in the eastern and northern sectors of the dam, while the western sector is deforming evenly. Moreover, although the horizontal deformation had a slowdown from 2010 until 2013, it continued in 2014 to 2019 with recovered intensity. The upper and the recent embankments are affected by major settlements, possibly due to a lower consolidation degree of the most recent tailings and a larger thickness of compressible materials.

Feature Engineering for Surrogate Models of Consolidation Degree in Additive Manufacturing

Surrogate models (SM) serve as a proxy to the physics- and experiment-based models to significantly lower the cost of prediction while providing high accuracy. Building an SM for additive manufacturing (AM) process suffers from high dimensionality of inputs when part geometry or tool-path is considered in addition to the high cost of generating data from either physics-based models or experiments. This paper engineers features for a surrogate model to predict the consolidation degree in the fused filament fabrication process. Our features are informed by the physics of the underlying thermal processes and capture the characteristics of the part’s geometry and the deposition process. Our model is learned from medium-size data generated using a physics-based thermal model coupled with the polymer healing theory to determine the consolidation degree. Our results demonstrate high accuracy (>90%) of consolidation degree prediction at a low computational cost (four orders of magnitude faster than the numerical model).

Simplified Method for Consolidation Settlement Calculation of Combined Composite Foundation

Treating weak saturated soil foundation by drainage powder jetting pile foundation can not only increase the bearing capacity of the foundation but also accelerate the drainage and consolidation process of the foundation. Having been commonly used in engineering, the plum blossom pile layout scheme is based on the foundation axisymmetric consolidation model (the powder jetting pile is the model center and the drainage board is located at the outer boundary of the model). It adopts reasonable boundary conditions and foundation seepage conditions and the method of pile-soil composite modulus and obtains the expression of the average excess pore water pressure of the composite foundation of the instantaneous loading of the drainage powder jetting pile under the simplified model. Therefore, the average consolidation degree of the foundation is acquired. The expression of the average consolidation degree can comprehensively reflect factors such as pile-soil modulus ratio, displacement ratio, drain spacing ratio, and those which affect the consolidation process of the foundation. The obtained analytical solution is of certain practical application significance for the consolidation settlement calculation of such engineering.

Tingkat Konsolidasi Penurunan Lahan Berdasarkan Metode Asaoka di Lahan Area 1B Blok J di Lokasi JIIPE, Manyar, Gresik, Jawa Timur

Tingkat konsolidasi pada lahan lunak dapat ditentukan dengan menggunakan Metode Asaoka (1978). Metode ini dipilih karena penerapannya yang sederhana dan memiliki tingkat akurasi yang dapat diandalkan, merujuk kepada hasil penelitian-penelitian lain. Observasi penurunan lahan dilakukan di Area 1B Blok J, di lokasi JIIPE, Manyar, Gresik Jawa Timur. Metode Asaoka merupakan suatu teknik untuk memperkirakan penurunan tanah dengan menggunakan grafik curve fitting, yaitu proses data-smoothing, pendekatan terhadap kecenderungan data dalam bentuk persamaan model matematika; biasanya digunakan untuk keperluan interpolasi. Dengan cara ini, kebutuhan akan data lapangan dan data pendukung seperti: data laboratorium berupa tekanan air pori, panjang aliran air, koefisien konsolidasi dan regangan maksimum tanah, tidak diperlukan. Validasi data dilakukan dengan memperbandingkan tingkat konsolidasi yang dihasilkan berdasarkan pengamatan dari metode Asaoka dengan desain teknis engineering. Hasil penelitian menunjukkan bahwa tingkat konsolidasi yang dihitung dari observasi data menggunakan metode Asaoka adalah 96.93% yang terbukti lebih besar daripada desain teknis engineering (95%).Kata kunci: kawasan industri,metode Asaoka, tanah lunak, tingkat pemadatanConsolidation rate on soft soil can be determined using the Asaoka Method (1978). In this study, the method was chosen because of its simple application and has a reliable level of accuracy, referring to the results from other studies. Observation of ground settlement was taken from Area 1B Block J located in JIIPE, Manyar, Gresik, East Java. The Asaoka method is a technique for estimating ground settlement using curve-fitting graph: a process of data-smoothing, approach of data trends in the form of mathematical equations; usually used for interpolation purposes. With this technique, the needs for field data and supporting data such as laboratory data in the form of pore pressure, water flow length, consolidations coefficient, and maximum soil strain, are not required. Data validation is done by comparing the degree of consolidations results based on Asaoka Method observation with the technical design of engineering. The result shows that the consolidation degree calculated from Asaoka Method observational data was 96.93%, which is proven greater than the technical engineering design (95%). Keywords: industrial estate,Asaoka method, soft soil, consolidation degree

Effect of a vacuum gradient on the consolidation of dredged slurry by vacuum preloading

In this paper, a large-scale indoor model test was carried out to reinforce the dredged slurry by vacuum preloading, and the effect of the vacuum gradient on the reinforcement effect was studied. The vacuum pressure, volume of extracted water, average ground settlement and pore water pressure were monitored during the test. After the test, the water content and vane shear strength were measured, and a particle analysis test and a scanning electron microscopy test were carried out. The results indicated that a small vacuum gradient could improve the consolidation degree and strength of the soil, and the smaller the vacuum gradient is, the better the reinforcement of the soil is. In addition, reducing the vacuum gradient could decrease the differential settlement of the soil surface and alleviate the migration of fine particles to the prefabricated drainage plates; therefore, the small vacuum gradient improved the clogging of the prefabricated drainage plates and the uniformity of soil consolidation. However, reducing the vacuum gradient also extended the test period, and a vacuum gradient of 20 kPa obtained the fastest consolidation rate of the soil.