Probabilistic prediction of expected ground condition and construction time and costs in road tunnels

Ground condition and construction （excavation and support） time and costs are the key factors in decision-making during planning and design phases of a tunnel project. An innovative methodology for probabilistic estimation of ground condition and construction time and costs is proposed, which is an integration of the ground prediction approach based on Markov process, and the time and cost variance analysis based on Monte-Carlo （MC） simulation. The former provides the probabilistic description of ground classification along tunnel alignment according to the geological information revealed from geological profile and boreholes. The latter provides the probabilistic description of the expected construction time and costs for each operation according to the survey feedbacks from experts. Then an engineering application to Hamro tunnel is presented to demonstrate how the ground condition and the construction time and costs are estimated in a probabilistic way. In most items, in order to estimate the data needed for this methodology, a number of questionnaires are distributed among the tunneling experts and finally the mean values of the respondents are applied. These facilitate both the owners and the contractors to be aware of the risk that they should carry before construction, and are useful for both tendering and bidding.

Predictability of well construction time with multivariate probabilistic approach

Current univariate approach to predict the probability of well construction time has limited accuracy due to the fact that it ignores key factors affecting the time.In this study,we propose a multivariate probabilistic approach to predict the risks of well construction time.It takes advantage of an extended multi-dimensional Bernacchia–Pigolotti kernel density estimation technique and combines probability distributions by means of Monte-Carlo simulations to establish a depth-dependent probabilistic model.This method is applied to predict the durations of drilling phases of 192 wells,most of which are located in the AustraliaAsia region.Despite the challenge of gappy records,our model shows an excellent statistical agreement with the observed data.Our results suggested that the total time is longer than the trouble-free time by at least 4 days,and at most 12 days within the 10%–90% confidence interval.This model allows us to derive the likelihoods of duration for each phase at a certain depth and to generate inputs for training data-driven models,facilitating evaluation and prediction of the risks of an entire drilling operation.

Acoustic emission monitoring of rockbursts during TBM-excavated headrace tunneling at Jinping Ⅱ hydropower station

To better understand the mechanical properties of marble at Jinping II hydropower station, this paper examines the changes of brittle rocks in excavation damaged zones(EDZs) before and after excavation of tunnel with the tunnel boring machine(TBM). The paper attempts to employ the acoustic emission(AE) to study the AE characteristics and distribution of rockburst before and after TBM-excavated tunnel. It is known that the headrace tunnel #2, excavated by the drill-and-blast(D&B) method, is ahead of the headrace tunnel #3 that is excavated by TBM method. The experimental sub-tunnel #2–1, about 2000 m in depth and 13 m in diameter, between the two tunnels is scheduled. In the experimental sub-tunnel #2–1, a large number of experimental boreholes are arranged, and AE sensors are installed within 10 m apart from the wall of the headrace tunnel #3. By tracking the microseismic signals in rocks, the location, frequency, quantity, scope and intensity of the microseismic signals are basically identifed. It is observed that the AE signals mainly occur within 5 m around the rock wall, basically lasting for one day before tunnel excavation and a week after excavation. Monitoring results indicate that the rockburst signals are closely related to rock stress adjustment. The rock structure has a rapid self-adjustment capacity before and after a certain period of time during tunneling. The variations of rock stresses would last for a long time before reaching a fnal steady state. Based on this, the site-specifc support parameters for the deep tunnels can be accordingly optimized.

Effect of Various Alumina Powders on Properties of Castables

To satisfy the requirements of alumina castables in specific environment and enhance their properties,alumina castables were prepared using tabular alumina,various alumina powders(07RAL,15RA,22RABL,40CA,99-20um,and 99-325mesh),and calcium aluminate cement as main raw materials,and heat treating at 110,1000,1600℃,respectively.Their flowability and physical properties were tested,and the morphology was researched.The results show that compared with calcined alumina and tabular alumina powders,reactive alumina has higher specific surface area and better filling performance leading to lower water demand and higher viscosity,and the castables prepared with reactive alumina have higher CCS and CMOR after heat treating at 110,1000 and 1600℃as well as lower PLC than those with calcined alumina and tabular alumina powders.

Bending behavior of double-row stabilizing piles with constructional time delay

The bending behavior of double-row stabilizing plies is associated with the constructional time delay(CTD),which can be defined as the time interval between the installations of the front stabilizing pile and the rear stabilizing pile.This paper investigates the effect of CTD on the bending moments of double-row stabilizing piles and a method for determining the optimal CTD is proposed.The stabilizing pile is modeled as a cantilever pile embedded in the Winkler elastic foundation.A triangular distributed earth pressure is assumed on the pile segment in the sliding layer.The front stabilizing pile and the rear stabilizing pile are connected by a beam with pinned joints.The analytical solutions of bending moments on the front and the rear stabilizing piles are derived and the accuracy of bending moment solutions is validated by comparing the tensile strain measured from the Hongyan landslide project,Taizhou,Zhejiang,China.It is concluded that CTD has a significant influence on the bending moments of double-row stabilizing piles.An optimal CTD can be obtained when the maximum tensile stress in the front stabilizing pile is equal to that in the rear stabilizing pile,which is 1.4 months for the Hongyan landslide project.

Gas field construction on time

About one--fOurth of the con- sery’e capacity at l00 billion cubic me-struction on China’s largest off shore tres.drilling field is now complete. and en- By January 30. more than 240gineers say the projcct is on schedule kilo1netres ol’ underu:ater pipelinestbr opening January l. l996. u:ere laid. about one fourth of the to-The Ya l3-- l Gas Field in the ta1. according yesterday’s o\’erseas edi-South Chlna Sea wiIl suppl} Hong tion or People’s Dall}’.Kong and Hainan Province w’ith natu- Exentually tuo underuaterral gas. Estimates put the tield’s re- pipeIInes ’’iIl he constructedt one.