Search

Lunar exploration has become increasingly popular, and lunar habitation research must be a core focus during the exploration of the Moon. The lunar habitation research must mainly include architectural and structural designs built using suitable material-forming technology and construction equipment. To address these issues, Chinese Super Mason (CSM) was proposed. This technology is an autonomous robotic construction system that is capable of automated assembling on-site prefabricated multistructural bricks and arched segments. The compound fabrication system was composed of a six-axis robotic manipulator and a dry mixed autoclaving fabricator carried on an autonomous-limbed vehicle platform. The Xuanwu Station for the lunar habitation conceptual design was developed and intended for erection by the CSM. A case study was conducted in a 2.8 m-long, 0.8 m-wide, and 1.1 m-high open arched-formwork structure fabricated within 8.5 h on the Earth. In addition, the Xuanwu Station was evaluated using finite element analysis software considering the temperature, air pressure, and other special environments on the Moon. The reliabilities and limitations of the CSM method were analyzed. Finally, the applications of the CSM in the extreme environment of the Earth and several improvements of the experimental equipment were discussed along with the proposed future applications for autonomous construction.

This study deals with the variation in strength of clays stabilized by a special binder—the CEM II/B-V type of Portland-fly ash cement. Two sources of uncertainties were examined, that is, the uncertainty in cement fraction in the binder, and the nonuniformity in binder concentration resulted from the process of mixing binder slurry with in situ clays. These two uncertainties were quantitatively described as two random variables, and the analyses were conducted through the Monte Carlo simulation method. Results indicate that the strength is insensitive to the cement fraction in the binder but is sensitive to the binder concentration; the variation of the latter even results in an amplified variation of strength. The variation of binder concentration is proposed to be linked up with the variation of strength through the operational parameter of blade rotation number. By doing so, the results could benefit designers in quality control prior to the construction of soil stabilization.

Excavation of a superlarge diameter tunnel by tunnel boring machine (TBM) is different from that of a shield tunnel with normal dimension, in which the control system of the superlarge TBM is very complicated and difficult to operate. Hence, it is very important to focus on the control and management of significant parameters to ensure excavation stability under uncertainty. In this paper, we (i) utilize a BIM-based big data platform (BIM-BDP) to manage the essential construction data of tunnel project in digital format; (ii) adopt the global sensitivity analysis (SA) to recognize significant parameters for shield excavation based on polynomial chaos expansion (PCE)–extended Fourier amplitude sensitivity test (eFAST) model; and (iii) employ the uncertainty analysis (UA) to discover the correlation between significant parameters from the data of the BIM-BDP. This research contributes to (i) the body of knowledge of proposing a more appropriate research methodology that can cope with aleatory and epistemic uncertainty and support uncertainty and sensitivity analysis (UA/SA) processes based on data from BIM-BDP and (ii) the state of practice by providing a data-driven surrogate model to simulate system behaviors of shield excavation with high reliability and to reduce dependency on domain experts. Here, we pay close attention to the most influential parameters that require priority parameter control, which can help administrators optimize the management of shield parameters during tunnel excavation.

Randomness in construction material properties (e.g. Young’s modulus) can be simulated by stationary random processes or random fields. To check the stationarity of commonly used techniques, three random process generation methods were considered: Xn(t), Yn(t), and Zn(t). Methods Xn(t) and Yn(t) are based on a truncation of the spectral representation method with the first n terms. Xn(t) has random amplitudes while Yn(t) has random harmonics phases. Method Zn(t) is based on the Karhunen-Loeve expansion with the first n terms as well. The effects of the truncation technique on the mean-square error, covariance function, and scale of fluctuation were examined in this study; these three methods were shown to have biased estimations of variance with finite n. Modified forms for those methods were proposed to ensure the truncated processes were still zero-mean, unit-variance, and had a controllable scale of fluctuation; in particular, the modified form of Karhunen-Loeve expansion was shown to be stationary in variance. As a result, the modified forms for those three methods are advantageous in simulating statistically homogenous material properties. The effectiveness of the modified forms was demonstrated by a numerical example.

Slurry pressure balance shield, a kind of tunnel boring machine, is significantly affected by the operation parameters such as advance speed and torque. In this study, a dynamic regulation model is established based on wavelet transform and bidirectional long short-term memory method (Bi-LSTM) to predict advance speed and torque. For comparison, twenty parameters of the shield machine are input to predict the tunneling behavior through the Bi-LSTM model and the LSTM model. Comparison results indicate that the proposed model has a relatively high accuracy. Moreover, parametric sensitivity analysis is made to filter the parameters by using light gradient boosting machine, so that the ranking of importance for all parameters can be gained. The proposed dynamic regulation model is validated by the Sutong gas-insulated transmission line project in China with a complex underwater-work condition, which has a guiding significance in operating and adjusting the shield machine in a dynamic process.

The artificial ground freezing method can be used jointly with the deep cement mixing method during break-in and break-out processes of shield machines in a tunnel shaft. The frozen ground can fully cut off groundwater seepage, thus ensuring a watertight working platform. Cement-admixed soils can restrict frost heave and thaw-induced settlement because of the decreased permeability. Both methods can also enhance mechanical strength of the soil to enable construction to proceed. Two main sources of heterogeneity are likely to influence the freezing effect: spatial variability in in situ water content in natural soil and spatial variability in binder concentration in cement-admixed soils. Furthermore, positioning error when installing freeze pipes can also affect freezing efficiency. This study simulates in situ water content and binder concentration as Gaussian random fields, whereby variations in the thermophysical properties are estimated. Positioning error is also assessed by prescribing an incline angle in freeze pipes. The influences of those two sources of spatial variability as well as positioning error are examined with random finite-element analyses and statistical characteristics are estimated based on the results. Results are tabulated to offer practitioners a rule of thumb for estimating additional efforts needed in artificial ground freezing, accounting for variations in the thermophysical properties and positioning errors in installing freeze pipes.

From a practical perspective, it is necessary to consider multivariate failure mechanisms in reliability analysis. The multivariate in a system may be dependent on each other, which should be considered in reliability analysis. To investigate the reliability of a structural system, this study develops a copula-based approach to construct dependence structures of different failure mechanisms. Herein, a novel two-step parameter estimation method based on a hybrid-evolution Markov chain Monte Carlo (MCMC) algorithm has been developed to estimate copula parameters with high accuracy and less bias. To verify the validity and robustness of proposed method, the face stability issue in shield tunneling has been used as an illustrative example. Results indicate that: (1) the novel two-step parameter estimation method yields reasonable parameter values; (2) the calculated values based on copula model are more accurate than Nataf model in practical engineering; (3) the failure probability pf calculated by copula model is obviously different (almost over 50% in both examples) from Independent scenario. The proposed reliability analysis using the copula model provides guidelines for face stability control under uncertainty and randomness, which can reduce the failure probability ahead of time and mitigate risk magnitudes to some degree after failure occurrence.

For reducing embankment load on box culvert, a new culvert structure called load shedding culvert (LSC) is proposed. First, model tests were conducted to investigate the performance of LSC, which was compared with embankment-installation box culvert (EBC) and imperfect-trench-installation box culvert (IBC). Then, numerical simulations were performed to investigate the stress states of the three culvert structures and associated important influencing factors. This study reveals that the LSC, compared with EBC and IBC, can not only reduce the vertical earth pressure on the top slab but also reduce the horizontal earth pressure on the culvert sidewall.

This paper introduces a near real-time digital method of circular tunnel shield segment assembly quality inspection using point cloud data (PCD) since the conventional manual inspection is untimely and incomplete for a segment assembly process. A three-dimensional (3D) laser scanner is used to capture the geometry information of newly assembled segment-rings via segment-ring PCD (srPCD). With a focus on dislocation and deformation, customized algorithms for segment-rings are proposed, including srPCD pre-processing, segment seam PCD extraction and dislocation and deformation calculation. The dislocation between adjacent segments within one ring and that between adjacent rings as well as the single ring ovality are inspected forthwith. A particular srPCD calculation software is developed based on the proposed algorithms and is implemented in a case study of a practical shield tunnel project. The inspection results validate the effectiveness of the proposed digital method and its advantages over the traditional way, signifying that the dislocation between adjacent rings is most likely to overrun during the assembly process. The error status and variation tendency of the segment-ring dislocation and deformation can also be observed on the srPCDs from progressive measurements when the segment-rings are supported by the shield shell. These show the benefits of the proposed method for shield tunnel construction quality management.

Deep cement mixing (DCM) is usually used for in-situ ground treatment for weak soil. The highly variable strength within DCM columns, remains a problem in engineering practice. Precious studies of physical modeling on DCM, only used single-shaft. However, in real DCM, a multi-shaft system, usually with dual or four shafts, is adopted. This paper presents the development of a dual-shaft DCM apparatus for centrifuge model testing. Centrifuge model tests were conducted to study mixing uniformity of DCM columns and considerable test data was obtained. The test results regarding mixing uniformity of the dual-shaft system are compared with those by single-shaft system. Some findings on the advantages and limitations in using dual-shaft deep mixing system are pointed out and considerations for further improvement are proposed.