Comparative research on the pipe-soil frictional resistances of circular and rectangular pipe sections during trenchless pipe jacking.

Pipe jacking is a trenchless construction method to achieve forward tunneling and efficient construction of underground structure simultaneously without extensive surface excavation. In the process of pipe jacking construction, the jacking force provided by the hydraulic jacking equipment must overcome the frontal resistance of the cutter head and the frictional resistance between the pipe sections and formation at the same time. In particular, the pipe-soil frictional resistance increases with the increases of jacking distance, buried depth, pipe diameter and the complexity of jacking trajectory. Therefore, it is very important to correctly estimate jacking force in trenchless jacking engineering practice for the smooth implementation of pipe jacking, operation risk and comprehensive cost control. Firstly, the stress states of jacking circular and rectangular pipe sections in the soil are analyzed, and the key influencing factors of their pipe-soil frictional resistance are obtained respectively. Then, the pipe-soil frictional resistance of jacking the circular and rectangular pipe sections with the same external surface area in the dry sandy soil and coal granular layer are tested separately by using the self-developed multifunctional experimental apparatus during trenchless pipe jacking. The results show that the pipe-soil frictional resistances of jacking circular and rectangular pipe sections in the coal granular layer are always smaller than that in the sandy soil under the same experimental conditions, and the corresponding fitting calculation equation of pipe-soil frictional resistances are obtained respectively. Meanwhile, the modified calculation methods of the above pipe-soil frictional resistances are proposed respectively based on the relationship between the lateral pressure coefficient K and the buried depth of pipe section H. Moreover, the disturbed area of soil in the upper part of jacking circular pipe section presents an arc distribution, while the disturbed area of soil in the upper part of jacking rectangular pipe section presents a slightly concave distribution. Due to the different disturbance conditions of soil around the pipe section, the lateral pressure coefficient K should be corrected in the calculation equations of pipe-soil frictional resistance of jacking circular and rectangular pipe sections based on the discrete element numerical simulation analysis by EDEM software. Finally, the pipe-soil frictional resistances obtained by different methods in the sandy soil are compared and analyzed. The calculated values of the modified theoretical calculation method are very close to the experimental test values, while the other methods are smaller than the experimental test values, which makes the rationality of the modified theoretical calculation method of pipe-soil frictional resistance is verified, and some suggestions are also put forward for the value of some coefficients in the relevant empirical estimation equations. The above research achievements systematically compared the states of pipe-soil frictional resistances of jacking circular and rectangular pipe sections based on different research methods, especially for the correct evaluation of jacking force during trenchless pipe jacking, they could provide some valuable references and effective guidance for the subsequent research, engineering practice and further development of trenchless pipe jacking technology.

Distributed Filtering for Semi-Markov-Type Sensor Networks With Hybrid Sojourn-Time Distributions-A Nonmonotonic Approach.

This article examines the distributed filtering problem for a general class of filtering systems consisting of distributed time-delayed plant and filtering networks with semi-Markov-type topology switching (SMTTS). The SMTTS implies the topology sojourn time can be a hybrid function of different types of probabilistic distributions, typically, binomial distribution used to model unreliable communication links between the filtering nodes and Weibull distribution employed to depict the cumulative abrasion failure. First, by properly constructing a sojourn-time-dependent Lyapunov-Krasovski function (STDLKF), both time-varying topology-dependent filter and topology-dependent filter are designed. Second, a novel nonmonotonic approach with less design conservatism is developed by relaxing the monotonic requirement of STDLKF within each topology sojourn time. Moreover, an algorithm with less computational effort is proposed to generate a semi-Markov chain from a given Markov renewal chain. Simulation examples, including a microgrid islanded system, are presented to testify the generality and elucidate the practical potential of the nonmonotonic approach.

Distributed Robust Filtering for Wireless Sensor Networks with Markov Switching Topologies and Deception Attacks.

This paper is concerned with the distributed full- and reduced-order l 2 - l ∞ state estimation issue for a class of discrete time-invariant systems subjected to both randomly occurring switching topologies and deception attacks over wireless sensor networks. Firstly, a switching topology model is proposed which uses homogeneous Markov chain to reflect the change of filtering networks communication modes. Then, the sector-bound deception attacks among the communication channels are taken into consideration, which could better characterize the filtering network communication security. Additionally, a random variable obeying the Bernoulli distribution is used to describe the phenomenon of the randomly occurring deception attacks. Furthermore, through an adjustable parameter E, we can obtain full- and reduced-order l 2 - l ∞ state estimator over sensor networks, respectively. Sufficient conditions are established for the solvability of the addressed switching topology-dependent distributed filtering design in terms of certain convex optimization problem. The purpose of solving the problem is to design a distributed full- and reduced-order filter such that, in the presence of deception attacks, stochastic external interference and switching topologies, the resulting filtering dynamic system is exponentially mean-square stable with prescribed l 2 - l ∞ performance index. Finally, a simulation example is provided to show the effectiveness and flexibility of the designed approach.

Experimental research on the performances of water jet devices and proposing the parameters of borehole hydraulic mining for oil shale.

Oil shale is an unconventional energy source, and it is also a potential petroleum substitute. Nowadays, the energy shortage is becoming more and more prominent, oil shale has attracted the attention of energy researchers all over the world. Borehole hydraulic mining is an effective method to exploit the underground oil shale which has more prominent advantages than other conventional mining methods. Jet devices are the key component of borehole hydraulic mining, which include the straight cone nozzle, organ pipe nozzle and self-excited oscillation pulsed jet nozzle. Also, the reasonable mining parameters are also crucial in mining underground oil shale efficiency. The jet characteristics of the non-submerged water jet, submerged water jet, direct water jet, cavitating water jet, and pulsed water jet are also explained and compared based on theoretical analysis. The jet performance of the non-submerged water jet is better than the submerged water jet. Each type of jet devices has its own basic principles and optimal structural parameters. The best operating scheme of borehole hydraulic mining for underground oil shale is to use the pulsed water jet which is produced by the self-excited oscillation pulsed jet nozzle to break underground oil shale under the non-submerged condition. Moreover, the pulsed water jet should be placed parallel to the oil shale bedding. In addition, under the preconditions of ensuring the safety and reliability of the hydraulic mining equipment and pipelines connection, the jet pressure and jet flow should be raised as much as possible, so as to obtain the much higher mining efficiency. These results and conclusions can provide very valuable guidance for borehole hydraulic mining of underground oil shale.