A plane slide that occurred during construction of a national expressway in Chongqing, SW China

This paper presents a case study of a major landslide that occurred during the construction of a national expressway in Chongqing, southwestern China. The landslide was a typical plane failure associated with steep cutting in weathered mudstone and sandstone. The weathered mudstone block slipped down along the bedding interface of the mudstone and sandstone and formed an open gap that measured some 6 to 8 m high, by 2 to 7 m wide and 53 m long in the hillside slope. This study referred that the landslide was caused by the combined effect of the following factors: (a) an unsupported high and steep cutting in weathered mudstone; (b) an exposed bedding interface between the incompetent weathered mudstone and the competent sandstone that daylights within the cut slope; (c) the mudstone and sandstone bedding interface as a pre-existing folding tectonic shear plane of low shear strength; and (d) the possible presence of a ground water table in the weathered mudstone perched on the relative impervious sandstone bedding surface. The case study highlights the importance of engineering geological mapping during and immediately after the formation of a new cut slope. It also emphasises the importance of identification of the pre-existing tectonic shear planes along the mudstone and sandstone bedding interface in similar geological terrain.published_or_final_versio

金剛石鉆進能量與花崗巖地層風化程度的關系

Based on experimental data from a drilling process monitoring system instrumented with a hydraulic rotary drill rig in fill-weathered granite formation, the diamond penetrating energy was analyzed. The result shows that the distribution of the penetrating energy in fill-weathered granite formation agrees with that in common weathered granite formation. A negative correlation between the viscous energy, kinetic energy, total penetrating energy and the weathered degree of granite existed, and a positive correlation between the thrust force energy and the weathered degree was presented, which indicates that there is a well response between the penetrating energy and the weathered degree of rock. However, the kinetic energy, thrust force energy and viscous energy are limited in identification of formation because of different effects in various drilling modes. The specific energy of diamond drilling (SEDD) increased with the weathered degree of rock and the values of SEDD can be classified into corresponding range according to the weathered degree of rock. It is shown that the SEDD in rotary drilling is apparently less than the specific energy of percussive drilling (SEPD) in both fill soil and very strongly weathered granite formation. Reversely, the SEDD is much more than the SEPD in lightly weathered hard rock.link_to_subscribed_fulltex

Interface identification in weathered granite strata based on a instrumented drilling system

A hydraulic rotary drill instrumented with a drilling process monitoring system (DPM) was used for site investigation in Hong Kong weathered granite foundation engineering. The penetrating parameters such as effective thrust force, rotational speed, flushing pressure, penetrating rate and displacement of the bit were monitored in real time. A varied slope was defined as a significant index for identification of dominative and subsidiary interfaces in the granite site. The result from t-test shows that the confidence of the DPM in identification of the geotechnical interfaces is 99%. Besides, the analysis of variation of the penetrating parameters at the interfaces indicates that there are different fluctuations at the interfaces in the curves of the parameters with borehole depth. The response degree of effective thrust force and penetrating rate to the variation of rock strength at the interfaces is 81.82% alone.link_to_subscribed_fulltex

Theory and approach of identification of ground interfaces based on rock drillability index

Rock drillability index is a very key parameter in selection of drill bit type and determination of productivity in petroleum, mining and geology. Unfortunately, there are many limits in the current definition as well as experimental methods. Drillability is redefined and a new concept of drillability index is brought out from analysis. Under the new concept, the drillability index is defined as penetration rate under specific energy. Based on the coupling relationship among effective thrust, rotation speed, penetration rate and drillability index, a calculation formula is established. Besides, the sensitivity of the drillability index in identification of ground layer is analyzed and its physical signification is expatiated also. The result shows that the new index overcomes the blind area in the traditional concept and can be used in continuous identification of ground layer along borehole profile.link_to_subscribed_fulltex

Grouted jetted precast concrete sheet piles: Method, experiments, and applications

This paper introduces an innovative technology - grouted jetted precast concrete piling - that increases the efficiency of piling operations in coastal regions. The technology includes the following steps: (i) casting concrete piles factory-designed especially for jetting and grouting; (ii) jetting to drive the concrete piles with a crane on a floating ship or platform into soil; and (iii) grouting to enhance the sheet pile connections and to increase the pile bearing capacity. This technology was applied to a number of piling construction projects at the mouth of the Yellow River Delta in China, and this experience demonstrated that it is a robust, fast track, cost-effective, and environmentally friendly piling method. © 2006 NRC Canada.published_or_final_versio

A dual fracture model to simulate large-scale flow through fractured rocks

Discrete fracture network models can be used to study groundwater flow in fractured rock masses. However, one may find that it is not easy to apply such models to practical projects as it is difficult to investigate every fracture and measure its hydraulic parameters. To overcome such difficulties, a dual fracture model is proposed. Taking into account the hydraulic characteristics of the various elements of the fracture system, a hydrogeological medium is assumed to consist of two components: the dominant fracture network and the fractured rock matrix. As the dominant fracture network consists of large fractures and faults, it controls the groundwater flow in rock masses. Depending on the permeabilities of the in-fill materials, these fractures and faults may serve as channels or barriers of the flow. The fractured rock matrix, which includes rock blocks and numerous small fractures, plays a secondary role in groundwater flow in such medium. Although the small fractures and rock blocks possess low permeability, their numbers and their total porosity are relatively large. Therefore, they provide large volume for groundwater storage. In this paper, the application of the proposed model to simulate the groundwater flow for a hydropower station before and after reservoir storage is reported. The implications of the results on the design of the station are also highlighted.published_or_final_versio

Weathered rock characterization using drilling parameters

The characterization of weathered rocks by the use of drilling parameters is presented. Drilling parameters obtained from the drilling process monitoring system during the installation of soil nails into weathered rocks are used in this investigation. A new drilling index Pi, simplified from the concept of the specific energy, is used in an attempt to differentiate weathered rocks. With Pi, or the penetration rate, boundaries of weathered rocks between (1) soil and rock ranges, and (2) grade II and grade III rocks in accordance with the six-fold rock material decomposition grade are identified. For weathered rocks in the soil range, quantitative characterization has been established in this study by using the drilling parameters. An empirical equation has been established for estimating the standard penetration resistance N value from the drilling parameter Pi, which is used in turn to determine the Mohr-Coulomb friction angle based on the work of Schmertmann. Although this approach tends to yield a slightly larger Mohr-Coulomb friction angle than that from laboratory tests, results obtained in this attempt reveal that estimation of the Mohr-Coulomb friction angle from drilling parameters is attainable with reasonable accuracy.published_or_final_versio

Prediction of grout penetration in fractured rocks by numerical simulation

As fractures in rock significantly reduce the strength as well as the stiffness of the rock mass, grouting may be required to improve the performance of the rock mass in engineering or mining projects. During grouting, mortar of cement or other materials is injected into the rock mass so that the fractures can be filled up and the rock mass can act as an integral unit. Unlike water, grouts are usually viscous and behave as non-Newtonian fluids. Therefore, the equations describing the flow of grout are more complicated and the solutions are quite difficult to obtain. The problem is further aggravated by the fact that the fractures are mostly randomly distributed, and it is rarely possible to accurately define the fractures and the distribution patterns. In this paper, a numerical model is proposed for analyzing the grouting process. The model is based on the stochastic approach, and it can provide the depth of penetration and the fluid pressure due to the flow of grout, which is modeled as a Bingham fluid, in the fractured rock mass. Parametric studies have been carried out to investigate the effects of various factors on the depth of penetration, and a regression formula is developed for calculating the penetration depth. Experiments have been carried out and their results are used to validate the present method.published_or_final_versio

Laboratory study of soil-nail interaction in loose, completely decomposed granite

The technique of soil nailing is seldom used in stabilizing loose fill slopes because there is a lack of understanding of the interaction behaviour of nails in loose fills. A large-scale laboratory apparatus has been built to study the soil-nail interaction in loose fill materials. Pullout tests were performed in a displacement-rate-controlled manner on steel bars embedded in loose, completely decomposed granitic soils. The load-displacement curves have distinct peak values followed by a sharp decrease in the pullout force. The test results also show that the normal stress acting on the nail changes because of the volume-change tendency and arching effect of the soil being sheared around the nail. The post-peak decrease in the pullout force is mainly due to the reduction in the normal stress caused by the arching effect of soil around the nail. The conventional method of analysis tends to give a low interface friction angle and high interface adhesion. The correct interface parameters can be determined by taking the changes in the normal stress acting on the nail into account. © 2004 NRC Canada.published_or_final_versio