Vibration Effect Induced by Rock Breaking Technology Based on Dry Ice and Energy-gathered Agent in Trench Excavation

Rock breaking technology based on dry ice and energy-gathered agent has been developed and successfully applied in trench excavation for construction of oil pipeline. The vibration velocity waveform induced by this technology was monitored in site test to determine the attenuation law of vibration velocity with hypocentral distance. The results show that this rock breaking technology is effective method of trench excavation. It does not excessively damage the adjacent rock mass, ensuring the integrity of ditch walls. The vibration velocity induced by this technology is decay with the increase of hypocentral distance. At the hypocentral distance of 10m, the vibration velocity reduces to less than 20mm/s, which meets the requirements of the safety standard of blasting vibration in general buildings engineering. The results of this experiment have an important guiding effect on the field engineering practice and application of rock breaking technology based on dry ice and energy-gathered agent.

Geography and Sources

The second chapter describes the physical character of the study area in detail as a framework for understanding the analysis supplied in the chapters to follow. It also sets out the main sources drawn upon in the book, notably the physical remains of archaeology and the fabric of the historic landscape itself, as well as documentary sources such as Anglo-Saxon charter bounds, manorial records, deeds, legal records, and maps, which yield data about the use of space and about inhabitants’ perceptions, the latter particularly revealed by the field names and bynames coined by local people themselves, and by legal depositions dealing with contested ownerships and customary practices. Key archaeological sources include village earthworks, excavated and standing buildings, and botanical and zooarchaeological remains. Archaeological fieldwork carried out as part of the project is described, including fieldwalking, test pit and trial trench excavation, extensive buildings survey, and measuring the soundmarks of church bells.

Mindlin solution on ground deformation caused by the trench excavation during installation of concrete diaphragm wall panels

Concrete diaphragm walls (CDWs) are widely used as support of deep excavation in soft ground in urban areas. Ground deformation occurs during the excavation of trenches for the installation of the CDW panels due to ground stress release. This paper investigates the ground deformation during slurry trenching using Mindlin solution. The pressure of slurry used to protect the trench stability during excavation is simulated as a triangularly distributed load on the trench walls, the soil stress state is solved using Mindlin solution, and the horizontal and vertical ground displacement are obtained through integral transformation of ground strain. The rationality of the solution is verified through comparison between the analytical solution and field measurement. Sensitivity analyses are performed on soil elastic modulus, Poisson's ratio, trench excavation depth and panel length. Simplified formulation is proposed for the prediction of horizontal ground deformation. The impact of excavation stages and adjacent panels on the ground deformation is explored. The study finds that the Mindlin solution is able to provide an approximate solution on the ground deformation during slurry trenching, and the simplified formulation can be used to provide a fast estimate of the horizontal ground movement in engineering practice.

Constraining Paleoearthquakes by Combining Faulted Stratigraphy and Microgeomorphology: A Case Study on the Haiyuan Fault, Northwestern China

Surface-rupturing strong earthquakes will leave evidence distributed along fault zones. The combination of paleoearthquake trench excavation and faulted microgeomorphic analysis at the same site provides more comprehensive knowledge of paleoearthquakes than either method could accomplish alone. In this article, we report on our use of trench excavation and dating, together with a 5-cm resolution digital elevation model obtained from an unmanned aerial vehicle based on the structure from motion photogrammetry technology, to investigate the timing and size of strong paleoearthquake events in the Dashagou site near the west end of the Haiyuan fault, which ruptured in the 1920 Haiyuan earthquake. The result reveals that at least four strong paleoearthquake events with the same or even higher magnitude (including the 1920 Haiyuan earthquake) have occurred along the west end of the Haiyuan fault since the mid-Holocene. Event IV occurred shortly before 6.0 ka with a horizontal displacement of 4.27±1.50 m and a vertical displacement of 0.70±0.39 m. Event III occurred at approximately 4.65±0.45 ka with a horizontal displacement of 5.45±1.25 m and a vertical displacement of 0.38±0.23 m. Event II occurred at approximately 1.0 ka with a horizontal displacement of 3.86±0.90 m and a vertical displacement of 0.55±0.27 m. The most recent event was the 1920 Haiyuan earthquake, with a horizontal displacement of 2.15±0.82 m and a vertical displacement of 0.26±0.12 m. From the results of these four events, we can certainly conclude that the fault has mainly maintained the strike-slip kinematic pattern over the past 6 ka. These observations highlight the benefits of combining trench excavation and faulted microgeomorphology to gain a more complete understanding of paleoearthquakes.

Observed performance of three adjacent 48 m depth concrete diaphragm wall panels in silty soils

The performance of three adjacent 48 m depth concrete diaphragm wall panels in silty soils is measured throughout the complete process of the wall installation including trench excavation, trench concreting, and concrete hardening. The analysis of the field measurement data shows that the ground movement induced by the wall installation is a function of construction activities. The maximum lateral movement occurs during the trench excavation. The trench concreting reduces the lateral movement. Field measurement at the end of wall installation may not catch the value of the maximum lateral movement. The ground settlement continues to increase during the complete process of panel installation, but with a decreasing rate. Roughly 90% of the settlement occurs during the trench excavation. The ground movement is also closely related to the properties of subsurface strata. The weak superficial fill materials sustain high disturbance, which consequently results in relatively large ground movement. With current engineering means and methods and good construction workmanship, the ground movement can be well controlled. In the current project, the maximum lateral ground movement was controlled within 2.0 cm and the maximum settlement was controlled within 0.05% of trench depth.

Root dry matter mass and distribution of Florico grass under different grazing strategies

The objective of this work was to evaluate the variations in root dry matter mass (RDM) and the percentage distribution (PD) of the root density of Florico grass (Cynodon nlemfuensis) in the 0-40-cm soil layer, when managed under different grazing strategies. Two defoliation frequencies (90 and 95% light interception, as the criterion for allowing animals in the paddock) and two defoliation severities (post-grazing heights of 20 or 30 cm) were assessed. Four seasonal evaluations of the root system were performed between the winter of 2012 and the autumn of 2013, using the monolith and trench excavation technique, collecting 1-dm3 samples from soil surface down to a depth of 40 cm, in four sequential extracts of 10 cm each. Lower RDM values (0.69 g dm-3) were obtained in winter, with the four grazing strategies, whereas higher values were observed in spring (1.64 g dm-3), for the 30-cm post-grazing residue, and in autumn (1.63 g dm-3) for the 20 cm post-grazing residue, regardless of the light interception value. Between 52 and 66% of the RDM density was observed in the 10-cm layer, for all four grazing strategies, in all seasons.