Analysis of Deformation Characteristics of Filled Subgrade Treated by Micro-Pile

Deformation control of fill subgrade is a difficult point in the field of highway engineering. This article relies on the treatment project of micro-piles for subgrade deformation of K555 + 070～K557 + 710 section of Qingdao-Yinchuan Expressway. Settlement and stress monitoring was carried out at the toe of the roadbed, the shoulder, and the center of the roadbed. We use Midas/GTS modeling trial calculation. A new method to check the simulation results of the deviation rate is proposed. A calculation model of the stress and deformation of the subgrade in the whole life cycle is established. The results of comparative analysis, monitoring, and simulation are as follows. ① The compression and consolidation of the fill account for most of the settlement and deformation of the roadbed in the whole life cycle. ② Subgrade center settlement is the sensitive part of subgrade deformation. ③ After piles are added, the deformation extremes at the toe of the slope, the shoulder, and the center of the roadbed are all reduced by more than 96%. The research results can provide theoretical guidance for the analysis of the stress and deformation characteristics of the subgrade before and after the micro-pile treatment.

Prediction of gas pressure in thin coal seams in the Qinglong Coal Mine in Guizhou Province, China

Thin coal seams in mines usually lack gas data. Thus, preventing and controlling gas outbursts of thin coal seams are difficult. In this study, a coal structure index, which is used to express the damage degree of coal, was estimated by logging curve. In accordance with the contour line of the floor of the coal seam, structural curvature was calculated to express the complexity of the coal seam structure quantitatively. Subsequently, relationships among the burial depth, thickness, coal structure index, structural curvature were analyzed on the basis of the gas pressure of coal seam. The gas pressure values of the coal seams of Nos. 22, 24, and 27 in the study area were predicted by multiple linear regression (MLR) and were then verified and analyzed. The deviation rate of the MLR method was 6.5%–19.7%, with an average of 13.0%. The average deviation rate between the predicted value and the measured value was 11.6%, except for the measuring point of No. 2, which had a large deviation. Results show that the prediction accuracy of the aforementioned method is acceptable and has practical value in the prediction of gas pressure in thin coal seams without measured data. The results in the gas pressure prediction provide a basis for evaluating the risk of gas outbursts in thin coal seams.

Research on optimization of perforation parameters for formation fractures based on response surface optimization method

For staged multi-cluster fracturing, methods for controlling perforation friction to adjust the flow distribution of each cluster can effectively promote the uniform extension of multiple fractures but lacks a fast and quantitative optimization method for different perforation parameters of each cluster. By establishing a numerical model of single-stage three-cluster flow-limited fracturing under stress-seepage coupling, and based on the response surface optimization method, fully considering the impact of perforation parameters interaction among three perforation clusters, according to the regression equation fitted under the global response, the rapid optimization of perforation parameters of segmented multi-cluster fracturing model is realized. The results show that: in determining the three factors of the study, it is found that there is an obvious interaction between the number of intermediate cluster perforations and the number of cluster perforations on both sides, the number of cluster perforations on both sides and the diameter of intermediate cluster perforations, the response surface optimization method gives the optimal perforation parameter combination of three clusters of fractures under global response; When the perforation parameters were combined before optimization, the fracture length difference was 32.550m, and the intermediate perforation cluster evolved into invalid perforation cluster, when the perforation parameters were combined after optimization, the fracture length difference was 0.528m, the three perforation clusters spread uniformly, and there are no invalid clusters. At the same time, the regression equation under the response is optimized before and after the comparison between the predicted value of the equation and the actual simulation value. It is found that the estimated deviation rate of the equation before optimization is 1.2%, and the estimated deviation rate after optimization is 0.4%. The estimated deviation rates are all less, and the response regression equation based on the response surface optimization method can quickly optimize the perforation parameters. The response surface optimization method is suitable for the multi parameter optimization research of formation fracturing which is often affected by many geological and engineering factors. Combining with the engineering practice and integrating more factors to optimize the hydraulic fracturing parameters, it is of great significance to improve the success rate of hydraulic fracturing application.

A Novel Rotation-Structure Based Stick-Slip Piezoelectric Actuator with High Consistency in Forward and Reverse Motions

Under the same driving voltage and frequency, the forward and reverse motion inconsistency of stick-slip piezoelectric actuators would bring difficulty for subsequent control. To solve this problem, a rotation-structure based piezoelectric actuator with completely symmetric structure and two driving feet was initially proposed. By testing its output performances under various driving voltages and frequencies, it was confirmed that, although similar speeds could be achieved for forward and reverse motions, the maximum displacement and backward displacement in each step were still quite different. By analyzing the reasons leading to this difference, this actuator was further improved by using only one driving foot. The experimental results showed that the forward and reverse motion consistency of the improved actuator had been significantly improved. The deviation rate was only 1.6%, corresponding to a travel distance of 118.7 μm, obtained under the driving voltage of 100 V and driving frequency of 10 Hz. The comparison with some previously reported actuators further confirmed the advancement of this improved actuator.

Study on Cutting Chip in Milling GH4169 with Indexable Disc Cutter

The study and control for chip have a significant impact on machining quality and productivity. In this paper, GH4169 was cut with an indexable disc milling cutter. The chips corresponding to each group of cutting parameters were collected, and the chip parameters (chip curl radius, chip thickness deformation coefficient, and chip width deformation coefficient) were measured. The qualitative relationship between the chip parameters and cutting parameters was studied. The quadratic polynomial models between chip parameters and cutting parameters were established and verified. The results showed that the chip parameters (chip curl radius, chip thickness deformation coefficient and chip width deformation coefficient) were negatively correlated with spindle speed; chip parameters were positively correlated with feed speed; chip parameters were positively correlated with cutting depth. The maximum deviation rate between measured values and predicted values for chip curl radius was 9.37%; the maximum deviation rate for cutting thickness deformation coefficient was 13.8%, and the maximum deviation rate of cutting width deformation coefficient was 7.86%. It can be seen that the established models are accurate. The models have guiding significance for chip control.

Research on Simplified Calculation Method of Coupled Vibration of Vehicle-Bridge System

A modified moving loads’ model is proposed for the vehicle-bridge coupling vibration simulation. Taking the vehicle-bridge interaction model (VBI) as the reference, the accuracy and applicability of the three calculation models, namely, moving loads’ model, moving mass model, and spring-damper-mass model, are compared using the frequently-used railway simply-supported beam with a span of 32 meters as the research object. Influencing factors such as vehicle speed, mass ratio of vehicle and beam, and primary spring stiffness on the dynamic response of the vehicle-bridge system are discussed in detail. The results show that the moving load model has the best performance on the stability of the deviation rate, but its calculation results are smaller than the other two methods as well as the VBI. The values of the deviation rate for the moving mass model and the spring-damper-mass model are large, and the stability of those are insufficient in the range of 80%∼120% of the first resonance velocity. Except for that, the results of the two models are in good agreement with the VBI model. According to above analysis, a modified moving loads’ model with two amplification coefficients, namely, 1.10 for the range of 90%∼105% of the first resonance velocity and 1.05 for other velocities, are proposed, which has higher calculation efficiency and accuracy.

ANALISIS KETIMPANGAN PRODUKTIVITAS DAN DUALISME KETENAGAKERJAAN DI PROVINSI BENGKULU

The purpose of this study is to analyze labor productivity inequality and labor dualism in Bengkulu Province. The method used is descriptive analysis, equipped with class typology and elasticity of employment. We are using employment data from BPS publications. The results show that by dividing business fields into 17 sectors in 2018 and 2019, labor productivity inequality is awfully unequal, which is indicated by a very high standard deviation rate. Meanwhile, labor dualism is led by informal workers by a percentage of over 60%. More workers with primary education are absorbed in the informal sector, whereas educated workers are mostly taken in the formal sector. The highest coefficient of labor absorption elasticity for legal workers occurred in 2016 (3.14) and for informal workers in 2015 (1.73).Keywords: labor dualism, labor productivity

Research on the Pricing of Convertible bonds in China---Migration risk based on credit rating

At present, further research and exploration on credit risks are being carried out in the global field, and increasingly profound modern credit risks are exposed to the bond market. This requires that we cannot ignore the impact of credit rating migration risk on bond pricing, so as to adapt to the sustainable and healthy development of the bond market under the new normal of China's economy. The innovation point of this paper is to try to analyze the pricing of Convertible bonds in China from the perspective of credit rating migration risk. Tsiveriotis and Fernandes(1998) model is selected, and the credit risk in the model is assumed to be caused by the credit rating migration risk, and the credit spread is used to measure the credit rating migration risk. The research conclusion of this paper is as follows: First, it is valid to consider the risk of credit rating migration in the TF(1998) model. The market price of convertible bonds is on average 1.22% higher than the theoretical value of the model. In general, the theoretical value obtained from the model has little deviation from the market price, and has a good fitting degree. Second, from the Angle of credit rating, the selection of 32 samples of convertible bonds only empirical research shows that the credit rating of AA - convertible bonds average deviation rate is negative, suggest that the credit rating of AA - the phenomenon of convertible bonds value is underestimated, and AAA credit rating to AA, AA +, the average deviation rate of convertible bonds is positive, that credit rating AA (containing AA) more convertible bond value is overrated phenomenon, and the higher the credit rating of the average deviation rate of convertible bond, the greater the overvalued levels. It has certain guiding significance for participants in the convertible bond market.