Full-Scale Field Test On Retaining Structure Enhanced With Soil Nails And Prestressed Anchors

Retaining structure enhanced with soil nails and prestressed anchors is found good at constraining the horizontal displacement and therefore ensuring the stability of the foundation pit during excavation. Based on these advantages, such retaining structure is widely used in foundation excavation practice. This paper presents results of a series of in-situ tests conducted to investigate the mechanical behaviors of retaining structure enhanced with soil nails and prestressed anchors. Behaviors of three different retaining structures enhanced with i) soil-nails; ii) soil-nails and prestressed anchors without unbonded part; iii) soil-nails and prestressed anchors with a 2.5m unbonded length, were monitored during staged excavation to investigate the influences of i) the prestressing force and ii) unbonded length of the prestressed anchors on the performance of the entire retaining system. It was found that the affecting the stress and deformation of composite retaining system, which is in agreement with the other published results in the literature. The variation of the magnitude and distribution of soil nail force responding to the anchor prestressing force however showed no systematic trend. The unbonded length of anchors, which is suggested to be the main factor affecting the structural stability in dense materials in the literature, is found to have little influence in loose fill materials used in this study. Studies presented in this paper are useful for the rational design and serviceability analysis of the composite soil-nailed retaining structure enhanced with prestressed anchors.

Application of Machine Learning Model for the Prediction of Settling Velocity of Fine Sediments

Sedimentation management is one of the primary factors in achieving sustainable development of water resources. However, due to difficulties in conducting in-situ tests, and the complex nature of fine sediments, it remains a challenging task when dealing with issues related to settling velocity. Hence, the machine learning model appears as a suitable tool to predict the settling velocity of fine sediments in water bodies. In this study, three different machine learning-based models, namely, the radial basis function neural network (RBFNN), back propagation neural network (BPNN), and self-organizing feature map (SOFM), were developed with four hydraulic parameters, including the inlet depth, particle size, and the relative x and y particle positions. The five distinct statistical measures, consisting of the root mean square error (RMSE), Nash–Sutcliffe efficiency (NSE), mean absolute error (MAE), mean value accounted for (MVAF), and total variance explained (TVE), were used to assess the performance of the models. The SOFM with the 25 × 25 Kohonen map had shown superior results with RMSE of 0.001307, NSE of 0.7170, MAE of 0.000647, MVAF of 101.25%, and TVE of 71.71%.

Live-Scale Testing of Granular Materials Stabilized with Alkali-Activated Waste Glass and Carbide Lime

The increasingly strong search for alternative materials to Portland cement has resulted in the development of alkali-activated cements (AAC) that are very effective at using industrial by-products as raw materials, which also contributes to the volume reduction in landfilled waste. Several studies targeting the development of AAC—based on wastes containing silicon and calcium—for chemical stabilization of soils have demonstrated their excellent performance in terms of durability and mechanical performance. However, most of these studies are confined to a laboratory characterization, ignoring the influence and viability of the in situ construction process and, also important, of the in situ curing conditions. The present work investigated the field application of an AAC based on carbide lime and glass wastes to stabilize fine sand acting as a superficial foundation. The assessment was supported on the unconfined compressive strength (UCS) and initial shear modulus (G0) of the developed material, and the field results were compared with those prepared in the laboratory, up to 120 days curing. In situ tests were also developed on the field layers (with diameters of 450 and 900 mm and thickness of 300 mm) after different curing times. To establish a reference, the mentioned precursors were either activated with a sodium hydroxide solution or hydrated with water (given the reactivity of the lime). The results showed that the AAC-based mixtures developed greater strength and stiffness at a faster rate than the water-based mixtures. Specimens cured under controlled laboratory conditions showed better results than the samples collected in the field. The inclusion of the stabilized layers clearly increased the load-bearing capacity of the natural soil, while the different diameters produced different failure mechanisms, similar to those found in Portland cement stabilization.

Experimental Study on the Compaction Characteristics and Evaluation Method of Coarse-Grained Materials for Subgrade

Coarse-grained materials are widely used in high-speed railway construction, and it is of great significance to research its compaction characteristics due to the high quality control requirements. In this regard, a field compaction experiment was conducted at a subgrade near Bazhou Station of Beijing-Xiong’an Intercity Railway. The test results of the compaction effect were presented in this study at first. The roller-integrated compaction measurements (i.e., compaction meter value, CMV) were compared with several traditional in-situ tests (i.e., plate load test, light falling weight deflectometer test, and shear wave velocity test). Then the stability of CMV was evaluated by the proposed δ criterion. The spatial uniformity of compaction was further investigated. Based on the analysis, the target value of CMV was preliminarily determined. It showed that Evd was more variable than CMV. The results convincingly indicated that the compaction parameters increased with the increasing number of roller passes at first. A further increase in compaction effort could result in the decompaction of material when the compaction number up to a certain value. The stability analysis method proposed in this study showed its potency of quantifying the percentage of areas with acceptable compaction. The geostatistical analysis could reflect the spatial uniformity of compaction. Overall, the conducted study could provide a useful reference for geo-material compaction control in the transportation engineering.

Determination of Relative Density and Degree of Saturation in Mineral Soils Based on In Situ Tests

Based on the results of dynamic probing (DP), time-domain reflectometry (TDR/MUX/MPTS), resistivity cone penetration tests (RCPT), Marchetti dilatometer tests (DMT), and seismic dilatometer tests (SDMT), it is possible to develop a relationship to calculate the relative density (Dr) and degree of saturation (Sr) of selected sandy soils. Compiled databases from documented research points for selected sandy soils were used to construct and develop direct correlations between the measured pressures p0 and p1 from DMT and shear wave velocity (Vs) from SDMT, along with pore water pressures (u0) and atmospheric pressure (Pa). The results allowed us to make a preliminary prediction when evaluating the parameters. Further, they allowed limiting the use of an additional device, especially in the case of multilayer heavy preconsolidated subsoils. Moreover, soil physical and mechanical characteristics (temperature, humidity, pressure, swelling, salinity) measured from TDR/MUX/MPTS (laboratory/field-operated meter for simultaneous measurements of soil moisture, matric potential, temperature, and salinity—bulk electrical conductivity) were assessed. The main achievement of this paper is the original proposal of using a new nomogram chart to determine the relative density and degree of saturation based on DMT and SDMT tests.

An Analytical Solution for Non-Darcian Flow on a Constant Head Packer Test in the Interlayer Staggered Zone

Groundwater flow in an aquifer has frequently been found to be non-Darcian by performing in situ tests. A novel analytic model is proposed in this study for describing the unsteady non-Darcian flow in a confined aquifer by taking advantage of the observed flow rate and injection pressure during the constant head packer test. A linearization approximation of the Izbash equation is used to approximate the nonlinear term in the governing equation. This analytic model is applied to describe the non-Darcian flow in the interlayer staggered zone at the Baihetan hydropower station, China. The test results inversed by the genetic algorithm show that non-Darcian flow happened during the test under the injection pressure 0.3 MPa with the power index n is 1.278, non-Darcian hydraulic conductivity k 1 is 1.613 × 10 − 5 cm/s and the specific storage S s is 9.757 × 10 − 5 m-1, respectively. The sensitivity analysis indicated that when the power index n or the specific storage S s is larger, and the hydraulic head will increase more slowly and needs longer to stabilize, but the non-Darcian hydraulic conductivity k 1 shows the opposite trend. Moreover, the hydraulic head is more sensitive to the power index n compared to other parameters at late times. The findings of this study reveal the non-Darcian flow during the constant head packer test and provide a simple and fast way to estimate parameters for more accurate seepage field simulation.

Dynamic to Static Modeling

Dynamic-to-static modulus conversion has long been recognized as a complicated and challenging task in reservoir characterization and seismic geomechanics, and many single- and two-variable regression equations have been proposed. In practice however, the form and constants of the regression equation are variable from case to case. I introduce a methodology for estimating the static moduli called dynamic-to-static modeling (DTS). The methodology was validated by laboratory tests (ultrasonic and triaxial compression tests) to obtain dynamic and quasi-static bulk and Young’s (elasticity) moduli. Next, rock deformation phenomena were simulated considering different parameters affecting the process. The dynamic behavior was further modeled using rock physics methods. Unlike the conventional dynamic-to-static conversion procedures, the method considers a wide range of factors affecting the relationship between the dynamic and static moduli, including strain amplitude, dispersion, rock failure mechanism, pore shape, crack parameters, poromechanics, and upscaling. A comparison between the data from laboratory and in-situ tests and the estimation results indicated promising findings. The accuracy of the results was assessed by the analysis of variance (ANOVA). In addition to modeling the static moduli, DTS can be used to verify the static and dynamic moduli values with appropriate accuracy when core data is not available.

Classification of historical buildings based on energy efficiency tests and comfort tests

The article presents a proposal for the classification of historic buildings in terms of improving energy efficiency, ensuring the comfort of users and their impact on the environment. In the case of historic buildings, Polish law does not require energy efficiency improvement. The proposed classification also takes into account the function of the object and is largely based on "in situ" research. The presented model of classification will help users of historic buildings to undertake appropriate thermo-modernization measures to improve energy efficiency and comfort of use. In situ tests in historic buildings are of particular importance also for the correct diagnostics of this type of buildings.

Improvement of Gas Drainage Efficiency via Optimization of Sealing Depth of Cross-Measure Boreholes

The sealing depth of a gas-drainage borehole is critically important as it directly affects the efficiency of the whole drainage system. In order to determine the shortest reasonable sealing depth, in this paper, a theoretical drainage model using different sealing depths was proposed. Based on theoretical analysis presented, two parts of the fractures system surrounding the drainage borehole were proposed, i.e. the fractures induced by roadway excavation and the fractures induced by borehole drilling. A series of geological in-situ tests and simulations research were conducted to determine the stress and fracture distributions in the surrounding rock of the borehole. The depths of crushing zones, plastic zones and stress concentration zones were determined as 5 m, 2 m and 12 m, respectively. Meanwhile, stress simulation shows that the depth of the stress concentration zone was 12 m from the roadway wall and the stress peak was located at the depth of 8 m, which can be verified by the results of drilling penetration velocity analysis. To determine the optimum sealing depth, gas drainage holes with different sealing depths were drilled in the field. The field results revealed that the crushing zones were the main area for air leakage, and the stress concentration induced by roadway excavation assisted in the reduction of air leakage. Therefore, the optimized sealing depth should both cover the plastic zone and the stress concentration zone. The research achievements can provide a quantitative method for the determination of optimum sealing depth in cross-measure drainage boreholes.