Clay is found in some countries all over the world. It usually has low compressive strength and cannot be used as a bearing material for subgrade soil. In this paper, the influence of basicity on a metakaolin-based polymer binder to improve clay was studied. The effects of the molar concentration of the alkali activator, different concentration of the metakaolin-based geopolymer and curing time on unconfined compressive strength were studied. The alkali activator-to-ash ratio was maintained at 0.7. The percentage of metakaolin added to the soil relative to metakaolin and soil mixture was 6%, 8%, 10% and 12%. The sodium hydroxide concentrations are 2M, 4M, 6M and 8M. Unconfined compressive strength (UCS) was tested on days 3, 7, 14 and 28, respectively. Compared with original clay, the results show that the unconfined compressive strength increases with the increase in metakaolin content and molar concentration of NaOH. The maximum compressive strength of the sample with NaOH concentration of 8M and percentage of 12% was 4109 kN on the 28th day, which is about 112% higher than that of the original clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the cementing compound covered the clay particles due to the reaction of the geopolymer with the clay, resulting in the formation of adhesive particles. The main purpose of this study is to verify the effectiveness and stability of metakaolin-based geopolymer binder polymerization under normal temperature and a strong alkali environment. The results can provide parameters for the application and promotion of metakaolin-based geopolymers in soil improvement engineering.

The vibration control system of a building structure under a strong earthquake can be regarded as a large complex system composed of a series of overlapping subsystems. In this paper, the overlapping decentralized control of building structure vibration under seismic excitation is studied. Combining the overlapping decentralized control method, H∞ control algorithm, and passive fault‐tolerant control method, a passive fault‐tolerant overlapping decentralized control method based on the H∞ control algorithm is proposed. In this paper, the design of robust H∞ finite frequency passive fault‐tolerant static output feedback controller for each subsystem is studied. The fault matrix of the subcontroller is expressed by a polyhedron with finite vertices. In order to reduce the influence of external disturbance on the controlled output, the finite frequency H∞ control is adopted and the Hamiltonian matrix is avoided. In this paper, the passive fault‐tolerant overlapping decentralized control method based on H∞ control algorithm is applied to the vibration control system of the four‐story building structure excited by the Hachinohe seismic wave. One drive is set on each layer of the structure, and a total of four drives are set. Select the driver fault factor of 0.5 or 1 and the frequency band [0.3, 8] Hz. The overlapping decentralized control scheme and 16 fault‐tolerant fault matrices are designed, and the numerical comparison results are given. The results show that both overlapping decentralized control strategy and multioverlapping decentralized control strategy have achieved good control results. Due to the different number of subsystems and overlapping information, the overlapping decentralized control scheme increases the flexibility of controller setting and reduces the computational cost.

In this paper, by using Lyapunov–Krasovskii stability theory and linear matrix inequality approach, the control problem for fractional-order systems under seismic waves with time-varying delays is studied. A novel switching surface is proposed. Based on the linear quadratic regulator and sliding mode control, some sufficient conditions are derived to ensure the fractional system under control. Mittag-Leffler stability theorem is adopted to prove that the switching surface could converge to zero. Finally, a numerical simulation example is provided to validate the advantages and effectiveness of the proposed results.

This paper presents an overlapping decentralized guaranteed cost hybrid control method for adjacent buildings with uncertain parameters, by combining the guaranteed cost control algorithm with the overlapping decentralized control strategy. The passive dampers are used as link members between the two parallel buildings, and the active control devices are installed between two consecutive floors in two adjacent buildings. The passive coupling dampers modulate the relative responses between the two buildings, and the active control devices modulate the interstory responses of each building. Based on the inclusion principle, a large-scale structure is divided into a set of paired substructures with common parts first. Then, the controller of each pair of substructures is designed by using the guaranteed cost algorithm. After that, the controller of the original system is formed by using the contraction principle. Consequently, the proposed approach is used to prevent pounding damage and achieve the best results in earthquake response reduction of uncertain adjacent buildings when compared with the calculation results obtained by the centralized control strategy. Furthermore, the stability and reliability of the control system are promoted by adopting the overlapping decentralized control strategy.

This paper proposes a discrete-time overlapping decentralized guaranteed cost control algorithm via state feedback. Based on the inclusion principle, a structure system is decoupled into multiple subsystems, and the discretized subsystems’ controllers are designed by using the guaranteed cost control algorithm. Finally, the subsystems’ controllers are contracted into overlapping controllers of the original system, and the design of the control system is completed. This control method is introduced to the civil engineering field to solve the seismic control problem for discrete-time systems of building structures with uncertain parameters. The numerical analysis of the nine-story building structure model with uncertain parameters is carried out. The results show that the proposed control method can still effectively reduce the seismic response of discrete-time system when the structural parameters are uncertain, and the control effect is similar to the centralized control strategy; at the same time, the sampling rate and data transmission speed of the system are improved to ensure the reliability of the system. It illustrates the feasibility and effectiveness of the presented approach.

Fracture of coal structure and low permeability were the main reasons for the “difficult to released gas” in broken soft coal seam. Exploration of horizontal well coalbed gas technology of roof and floor of broken soft coal seam provided a new technical way for coalbed gas development in broken soft coal seam. In this paper, taking Xinxie -1 drilling as an example, the evaluation method of fractured reservoirs in roof and floor of broken soft coal seam was improved. By systematic studied on mineralogy, petrology and engineering mechanics characteristics of top and bottom plates in broken soft coal seam, the influence of rock mineral composition on the rock mechanics properties of the roof and floor of coal seam was explored. In addition, By used correlation analysis and grey relational analysis, a brittle evaluation method of coal seam top and bottom plates based on mineral composition was established. The research results showed that: ①The main components of rock minerals in the top and bottom plates of broken soft coal seam were quartz and clay minerals, followed by plagioclase, siderite and pyrite. The main types of rock cementation were quartz enlargement and siderite cementation, and the pore damage caused by cementation was much greater than that of compaction; ②With the increased of rock particle size, compressive strength (CS) and elastic modulus (E) showed a gradual increase trend, Poisson's ratio (μ) showed a gradual decrease trend, other rock mechanical parameters had no obvious changes. The difference of mineral composition and cementation type was the key factor cause abnormal mechanical properties of rocks; ③Compared with clay minerals, the change of brittle mineral content such as quartz, plagioclase and siderite in rocks were sensitive to the mechanical properties of rocks. The sensitive minerals of compressive strength, shear strength, elastic modulus and softening coefficient were quartz, the sensitive minerals of compressive strength were plagioclase and siderite, and the sensitive minerals of Poisson's ratio are quartz and clay; ④The calculation results of the established mineral weight analysis method were more realistic. It could be concluded that the roof of 13-1 coal, 11-2 coal, 9-2 coal and 4-2 coal seams were more inclined to form fracture network during fracturing, which had guiding significance for the optimization of fracturing horizon.