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**File Type**

Wang, C.H. (Institute of Crustal Dynamics) | Guo, Q.L. (Institute of Crustal Dynamics) | Yang, S.X. (Institute of Crustal Dynamics) | Ding, L.F. (Institute of Crustal Dynamics) | Hou, Y.H. (Institute of Crustal Dynamics)

Building the underground water-sealed petroleum storage cavern is one important access to assure safe and stable national petroleum storage system. Considering these reasons, some national departments are planning to build one large-scale strategic petroleum storage project in Bohai Gulf. For the special underground structure features, magnitudes and orientation of far-field stresses of planned project area shall be studied in detail. The hydrofracturing measurements has been done in five boreholes of about 140m deep; for the scattered measurement results, it is hard to find out the intrinsic relationships between different measurement spots; therefore, the Shoerey’s Model is taken to process all the measurements, and then the magnitude of stresses at the cavern section is determined accurately; the maximum horizontal stress is 11.02±1.0MPa, and minimum horizontal stress is 6.82±1.0MPa; the orientation of maximum horizontal stress is 76°(±13°), which coincides with the findings by B. C. Haimson, et al. in Korea and the data from WSM, i.e., the orientation of far-field stresses in this region should be between WSW-ENE and E-W. The far-field stresses have few effects on the stability of underground structure according to the stress-to-strength ratio method proposed by Hoek E.; during the excavation, the linear elastic response is the major phenomenon in intact wall rock mass, but falling or sliding of blocks and wedges may occur in some local parts.

ISRM-SINOROCK-2009-059

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

borehole, calculation, cavern, discontinuity, Downstream Oil & Gas, Engineering, far-field stress, granite, Horizontal, in-situ stress, layer, moderately weathered, MPa, natural gas storage, orientation, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, stress, Tab, underground petroleum storage cavern, Upstream Oil & Gas

SPE Disciplines:

With the introduction of a new four-year degree program at The University of Hong Kong, a Centennial Campus is being developed at the western side of the existing Main Campus. The scope of this infrastructure project comprises the design, construction and commissioning of two new salt water and two new fresh water service reservoirs. Cavern was excavated in sandstone and tuff to accommodate the new salt water reservoir in a twin-cell tunnel system. The cavern was constructed inside a sloping ground due to the need to find adequate rock cover. Starting at the portal, an about 30 m long, 7.2 m span access tunnel was constructed and then separated into two reservoir tunnels. Two 10 m long transition zones were constructed and then the tunnels were enlarged from 7.2 m span to 17 m span to create the cavern for the new salt water reservoir. With the requirements of minimal damage and disturbance to the rock mass during the excavation, it provided an ample opportunity to study the convergence of the cavern as the excavation approached an undisturbed zone. This paper presents an evaluation of the magnitude of stresses acting on the crown of the large span tunnel at different stages of ground movement.

Back analysis was carried out based on the observed stresses and deformation resulted from approximately 6 m high top heading tunnel excavation. Two-dimensional finite element analysis program was utilized for this back analysis. Different empirical equations such as Bieniawski, Serafim and Pereira, Barton and Hoek et al. have been used in the numerical analysis to simulate the rock mass behaviors. It revealed that the Serafim and Pereira estimation was generally applicable for this particular HKU cavern project with volcanic tuff bedrock of as-mapped Q-value higher than 2.3 or RMR value higher than 50.

The observed monitoring records also demonstrated that approximately 2 mm of vertical deformation was mobilized to provide an efficient temporary support to the tunnel crown. Little stress relief and deformation was observed after the temporary rock support has been substantially mobilized.

This paper presents a case-study of the rock behavior due to the underground opening. It also demonstrated the performance of immediate support to the tunnel crown in controlling the ground settlement and stress relaxation.

ISRM-SINOROCK-2009-199

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

back analysis, cavern, change, construction, excavation, Hong Kong, management and information, Reservoir Characterization, reservoir description and dynamics, reservoir tunnel, rock, span, strain gauge, stress, structural geology, support, tunnel, tunnel crown, tunnel excavation, Upstream Oil & Gas

Oilfield Places: North America > United States > Texas > Permian Basin > Midland Basin > Davis Field (0.98)

SPE Disciplines:

A stress calculation method was proposed for the new stress measurement technique using the borehole slotter device. The 2D borehole slotter is an instrument which is used in HQ boreholes (96-104 mm diameter), and allows calculation of 2D stress tensor in a plane normal to the borehole axis. This instrument enables calculation of in-situ stress tensor using three boreholes without the need for mounting strain gauges on the borehole wall. The borehole slotter technique requires cutting of half moon shaped slots at different orientations parallel to the test hole axis using a small diamond impregnated blade and monitoring of the strains which are relieved normal to the slot direction. The aim of this paper is to evaluate the effects of key test parameters on the slotter test results. A precise 3D numerical model of typical slotter test condition was constructed using the FLAC3D code. The effects of variations in rock mass deformation modulus on the strain/stress relaxation, and thus borehole slotter test results, were investigated numerically. The validity of numerical findings were discussed and compared against practical observations. Accordingly, the borehole slotter tests conducted at Bakhtiari dam site-Iran was simulated numerically. A very good agreement was achieved between numerical and field test results. The obtained numerical results provided valuable insights in selecting the governing in-situ stress condition from the recorded field data.

Since the slotter technique has proven reliable in the field and has had certain commercial successes, attention is paid to improve the accuracy of the calculated stresses by considering complexities such as rock mass behavior and heterogeneities at the measurement point. The main goal of this paper is to demonstrate the mechanisms involved the in-situ stress measurement using the slotter technique. The process of in-situ stress measurements conducted at Bakhtiyari dam-Iran was successfully modeled demonstrating the validity of numerical approach in simulating the process.

(Figure in full paper)

Before, during, and after slotting, the circumferential strain is measured at the borehole wall in the vicinity of slot and the tangential strain is measured by a specially developed recoverable strain sensor (Fig. 1) (Foruria, 1987; Bock, 1984). The strain gauge is mounted at 15 degrees from the slot location according to the INTERFELS test procedure recommendation.

ISRM-SINOROCK-2009-094

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

A Regulation 33 Geotechnical Assessmnet was carried out for Castle Cement Limited, in accordance with the Quarries Regulations 1999, approved Code of Practice (ACoP), at their Grange Top Quarry near Ketton, Rutland, UK in 2008. The assessment identified a total of 10 tips within the quarry for which the operator faced various constraints and could not undertake operations practically and in accordance with a completely ‘low risk’ methodology. In order to reduce the impact of the constraints a methodology was formulated which entailed increasing stockpile height some by 100%, increasing face angles and utilizing rock fill for features such as noise bunds. The proposed methodology was categorized as a medium risk. Once the methodology had been formulated it was proven by a range of numerical models including limit state and finite element and probabilistic analysis relating to material parameters, slope angles, groundwater, precipitation and also impact on third parties. Finally, upon commencing works, a monitoring regime was put in place to ensure that the proven methodology could be observed and any divergences could be highlighted and input back into the probablistic analysis in order to devise a new way forward for that particular constraint.

(Table in full paper)

The report did not identify the stockpiles within the quarry to be significant hazards in accordance with the Approved Code of Practice (ASoP) and were described as generally small in volume. It was proposed that stockpiles within the quarry area be limited to less than 7.5m in height and graded in all cases to inherently safe angles of less than 22

The assessment comprised inspection and evaluation as follows:

- Qualitative assessment of the stockpiles and slopes were undertaken, providing a stability risk (potential for failure) and safety risk (consequences of failure) associated with the geotechnical characteristics at each location;
- The hazard associated with each feature was evaluated and classified as significant.

ISRM-SINOROCK-2009-157

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

SPE Disciplines:

Li, L.C. (Dalian University of Technology) | Li, G. (Dalian University of Technology) | Tang, C.A. (Dalian University of Technology) | Liang, Z.Z. (Dalian University of Technology) | Zhang, Y.B. (Dalian University of Technology)

In order to investigate the fracture development and the associated fluid flow in rocks, an improved flow-stress-damage (FSD) model, implemented with Rock Failure Process Analysis code (RFPA3D), is presented. The numerical code is based on linear elastic damage mechanics on mesoscopic scale and FEM. For simulating the complete progressive 3-D failure and macroscopic mechanical behaviors of rock materials, rock properties such as elastic constants, peak strength, and Poisson ratio are randomly distributed to reflect the initial random distributed weakness in mesoscopic scale. The improved FSD model is used to represent the permeability variation at the two stages (stress-dependent permeability for pre-failure and deformation-dependent permeability for post-peak stage) of rock matrix at the elemental scale. The fracture initiation, propagation, and coalescence in the rock sample and the seepage field evolution with stress and damage variation are represented visually during the whole failure process. The simulation results compare well with reported experimental results which indicate that RFPA3D incorporated with the improved FSD model is a valid tool in understanding the physical essence of the evolutionary nature of fracture phenomena as well as the fluid flow in rocks.

ISRM-SINOROCK-2009-085

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

coefficient, damage, flow in porous media, Fluid Dynamics, fracture, heterogeneous rock, hydraulic fracturing, Mech Min Sci, model, nullnullnullnullnullnullnull, numerical simulation, permeability, process, Reservoir Characterization, reservoir description and dynamics, rock, Rock Mech, sample, stress, three-dimensional failure process, Upstream Oil & Gas, variation, well completion

SPE Disciplines:

Chen, Yifeng (Laboratory of Water Resources and Hydropower Engineering, Wuhan University) | Mao, Xinying (Laboratory of Water Resources and Hydropower Engineering, Wuhan University) | Zhou, Chuangbing (Laboratory of Water Resources and Hydropower Engineering, Wuhan University)

The concrete faced rockfill (CFR) dam of the Shuibuya Hydropower Project, with the maximum height of 233 m, is up to now the highest CFR dam built in the world. During construction and after completion of the project, however, a group of cracks were discovered on the concrete face slabs, which is the major measure for seepage control of the dam. Though measurements have shown that the cracks would not endanger the safety of the dam, sensitivity analysis is still needed to predict the seepage behavior of the dam in partial or complete deficiency of the face slabs on a coupled hydro-mechanical (HM) basis. In this study, a coupled saturated flow and stress process was considered to investigate the effects of the concrete face slab deficiency on the seepage behavior and safety of the dam. The deformation response of the rockfills is described by using the Duncan-Chang nonlinear elastic E-B model, together with the Desai’s thin layer elements for the interface between the face slabs and the buffer material. The coupling effect of stress on hydraulic conductivity of the rockfill is described by the Gangi’s model, which is embedded in the code for saturated flow process formulated with an adaptive variational inequality for eliminating the singularity at the outlet seepage points and resultant mesh dependency.

During construction and after completion of the project, however, a large group of cracks were observed on the concrete face slabs, as shown in Figure 1. Since use of the face slabs is the major measure for seepage control of the dam, the seepage behavior may deteriorate by the cracks. Though field measurements show that the cracks would not endanger the safety of the dam, sensitivity analysis is still needed to predict the seepage behavior, deformation and stability of the dam for partial or complete deficiency of the face slabs, as a coupled hydro- mechanical (HM) process.

In this study, a coupled saturated flow and stress process was established based on Biot’s consolidation theory to examine the effects of the face slab deficiency on mechanical response and seepage behavior of the dam. The Duncan-Chang nonlinear elastic E-B model (Duncan et al. 1970) and Desai’s thin layer elements (Desai et al. 1984) are used to model the deformation characteristics of the rockfills and its interaction with the stiffer concrete face slabs.

ISRM-SINOROCK-2009-076

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.47)

Many theoretical and empirical failure criteria for rock found in the literature are stress-based. Moreover, current failure criteria are often not adapted to predicting fallout in an underground excavation as opposed to simply predicting failure, i.e., overstressing of the rock. A connection between observable and predictable behavior is often lacking. This could be addressed through deformation monitoring, which is often conducted in underground excavations, but this would also require a failure criterion based on deformation parameters. Based on uniaxial laboratory test data, this paper evaluates the stages of deformation, i.e., the stress-strain relation, and the critical states of deformation of tested hard rock specimens. This study identifies deformation parameters governing failure of hard rocks. Available failure criteria based on deformation parameters are also presented in this paper. Finally, critical deformation parameters for establishing a deformation-based failure criterion are proposed.

(Table in full paper)

Stage I: This stage occurs during the initial phase of loading.

ISRM-SINOROCK-2009-045

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

Artificial Intelligence, axial, axial strain, crack, crack closure, crack initiation, crack volumetric, damage, deformation, failure, initiation, lateral strain, machine learning, Reservoir Characterization, reservoir description and dynamics, rock, rock type, strain, stress, structural geology, syenite, Upstream Oil & Gas, volumetric strain

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)

An extensive site investigation program was carried out between 2002 and 2007 to characterise the rock mass at Forsmark Sweden, to assess its potential for hosting a used nuclear fuel repository at a depth between 400 and 700 m. Stress campaigns using both overcoring and hydraulic fracturing, including the hydraulic testing of pre-existing fractures were carried out to establish the in-situ stress state. Using only those measurements that had approximately the same Azimuth, the minimum horizontal stress from the overcoring measurements were compared to the minimum horizontal stress from hydraulic fracturing. The hydraulic testing was carried out using special testing procedures designed to minimise the risk for inducing horizontal fractures or fracture rotation. Despite these efforts the hydraulic fracturing results indicated that the minimum horizontal stress was approximately 50% of the magnitude given by the overcoring measurements and approximately equivalent to the vertical stress. It appears that the prominence of the open subhorizontal fractures at Forsmark combined with high horizontal stresses prevented both the hydraulic fracturing and HPTF from providing reasonable estimates of the minimum horizontal stress. The horizontal stress magnitudes from the overcoring were found to be in agreement with indirect measurements and observations made during the site characterisation program.

As noted by Doe et al. (2006) not all stress measurement methods carried out in deep boreholes will work in all geological environments. They note that in over-stressed rock, e.g., rock masses where the horizontal stresses significantly exceed the weight of the overburden (a thrust regime) none of the stress measurement techniques work particularly well. Because hydraulic fracturing produces a fracture normal to the minimum stress, hydraulic fracturing in such a stress regime tends to produce horizontal fractures and hence measures the weight of the overburden /Evans and Engelder 1989/. The overcoring method relies on elastic theory and in such a stress regime micro-cracking may occur inducing a nonlinear stress-strain response which makes it difficult to interpret the results (Martin and Christiansson 1991).

While it may be difficult to measure the in-situ stress state directly using traditional overcoring and hydraulic methods in some in-situ stress regimes (geological environments), the results from such measurement campaigns, nonetheless, contribute significantly to understanding the in-situ stress state at a site.

ISRM-SINOROCK-2009-039

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

borehole, campaign, Comparison, establish, Forsmark, fracture, fracture domain, fracture frequency, frequency, Horizontal, hydraulic fracturing, hydraulic method, in-situ stress, intermediate principal stress, Magnitude, orientation, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock mass, stress, Upstream Oil & Gas, vertical stress, well completion

SPE Disciplines:

The issue of prescribing the support requirements for stratified roofs of no major discontinuities otherthanhorizontalbeddingplanesisherebyapproached ideallyaswellaspragmatically. Firstly, the unreinforced case is analytically defined; the solution acquired by elementary beam theory for a fixed beam under distributed load is compared to an Airy stress function solution for a fixed beam under its own weight based on Timoshenko beam theory. Finally, a finite difference numerical solution is performed and verified. The model is then used to investigate the behavior of a two-member stratified roof with contact plane governed by the angle of friction and tightened inordertomobilizetheshearingreactionforceatthediscontinuity.Parametric analyses to investigatethepossibleeffectsofelasticparameterssuchasthe modulusofelasticityandthe Poisson’s ratio and also the interbedding friction angle and its effect on the response of the model conclude thissection. The last part involves the numerical implementation of a bolting support system providingthe previously determinedforce andthe prescription ofits characteristics,i.e. length,spacing,diameterandpretensionofbolts.The impact of applying concentrated compressive forces instead of the theoretical distributed support is also outlined.

(Equation in full paper)

The maximum stress components σ

The modeled plane strain beam was of L/t=12.5, zero Poisson’s ratio, 1 m length, density 2400 Mg/m

ISRM-SINOROCK-2009-123

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)

A The responses of some lined underground openings under hydrostatic or biaxial stress field are examined numerically for original HB and equivalent MC strength parameters. The rock mass is assumed brittle and the horizontal to vertical stress ratio is varied. Selected tunnel responses of the openings for the original HB rock mass are compared to the responses computed using equivalent MC strength parameters. These include the displacement at the crown and the side walls of the opening, the yielded zone formed around the tunnel and the internal forces within the tunnel lining. Results indicate the cases where deviations in the tunnel performance are computed.

Several methods have been developed for the evaluation of equivalent MC strength parameters for given HB ones. Traditionally, they are based on a linearization procedure of the HB strength envelope for a selected range of the minor principal stress. This range is either considered as independent of the in situ stress field (Hoek and Brown, 1997) or depends on it. In the latter case the internal pressure offered by the tunnel support may either be neglected (Hoek et. al., 2002), covering thus a wider range of rock mass responses, or taken into account (Sofianos and Halakatevakis 2002, Sofianos 2003, Sofianos and Nomikos 2006, Jimenez et. al. 2008), aiming to better approximate the final equilibrium condition of the tunnel.

Most of the existing methods are concerned with the case of an elastic-perfectly plastic rock mass. However, rock mass may exhibit a strain-softening behavior after failure. The importance of post-peak behavior of rock mass for rock engineering design has already been recognized (Hoek & Brown 1997, Russo et. al. 1998, Ribacchi 2000) and recently emphasized (Cai et. al., 2007), since it may have a strong influence on the stability of the underground excavations. Sofianos & Nomikos (2006) presented two methods, BFe and EMR, to calculate the equivalent MC rock mass strength parameters for axisymmetric tunnels in plastic or brittle rock. These are shortly described in the following.

ISRM-SINOROCK-2009-095

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

axisymmetric tunnel, bfe, displacement, EMR, equivalent, equivalent MC, equivalent MC rock mass, equivalent mc strength, field, mass, method, original hb, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, Response, rock, rock mass, strength, stress, support, tunnel, Upstream Oil & Gas

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

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