Weak Sedimentary Rocks Research Articles

Design of large-diameter drilled shafts for the Northumberland Strait bridge project

The Northumberland Strait bridge, recently named the Confederation Bridge, is a 12.9 km long bridge crossing Northumberland Strait between Borden, Prince Edward Island, and Bayfield, New Brunswick. The bridge must withstand large horizontal loads that are due to ice impact, wind, and wave action on the piers and superstructure. The abutment and the 14 shallow water approach piers located on the New Brunswick side of the strait are supported on groups of large-diameter drilled piles socketed into weak sedimentary rock. Pile designs are based on shaft resistance developed whithin the bedrock. Preliminary calculations indicated that piles were required with average socket lengths of about 13.5 m. A pile load test was carried out at the New Brunswick abutment for the purpose of refining the shaft design parameters. The pile load test was successful in allowing a 55% reduction in the average design socket lengths. (A)

Full-scale field experimentation of a new technique for protecting mudstone slopes, Taiwan

This paper documents a full-scale field experimentation of a new technique, called “green coating”, for protecting steep “mudstone” slopes. Mudstone is a weak sedimentary rock, formed during Miocene to Pliocene and Pleistocene. Many forms of geologic damage such as erosion, mudflow and slope failure are often seen in the mudstone area during the rainy season. This poses a great challenge to geotechnical engineers in Taiwan, as many large construction projects such as the Second National Expressway and the High Speed Railway are set to be constructed through the mudstone area. The field experiment is intended for validating the new technique which has evolved from experience generated from research projects conducted over the past decade. The new technique involves the use of two types of waterproof materials. One material is asphalt, and the other is geotextile sheets coated with asphalt. A mudstone hill is selected for treatment by the new technique. The total surface area of the cut slopes treated with the “green coating” technique is about 630 m 2. Engineering details of the treatment are presented in this paper. Two types of measurement are made to observe the movement and the inclination of the treated slopes. Based on the field observations and measurements, the treated slopes do not show any signs of significant erosion and movement. Thus, the new technique has been demonstrated to be an effective means for preventing erosion and failure of the mudstone slopes.

Formation of south-facing bald mudstone slopes in southwestern Taiwan

In the southwestern part of Taiwan, most foothills are covered by mudstones. The mudstone, formed during Miocene to Pliocene and Pleistocene, is a young and weak sedimentary rock. When subjected to water, slaking of the mudstone can easily take place and in dry seasons, severe shrinkage can occur. Thus, erosion of mudstone slopes is easily induced by rainfalls. Heavily eroded natural mudstone slopes in southwestern Taiwan frequently become “bald” (i.e. not covered by any plants or bushes) and are very susceptible to geologic damages such as mudflow and slope failure. One interesting observation of the mudstone slopes in southwestern Taiwan is that most of the bald slopes are south-facing. The causes of this directional variation are thoroughly examined in this paper. It is concluded that solar radiation, rather than the direction of typhoons, is the main reason for forming bald slopes in the south-facing direction.

Geotechnical investigations for a deep radioactive waste repository: in situ stress measurements

Abstract Comprehensive geotechnical investigations of potential repository sites for deep disposal of low- and intermediate-level solid radioactive wastes at Sellafield, Cumbria and Dounreay, Caithness included drilling and testing cored boreholes up to 2000 m deep. The investigation at Sellafield included the measurement of in situ stresses using the overcoring technique at various depths in a 250 m deep, vertical borehole drilled from the surface. The measuring instrument and method used for overcoring had, therefore, to perform reliably under high hydrostatic heads. The equipment used to carry out these measurements was the Swedish Borre Probe. Previous work with this equipment has been carried out in slim holes and hard crystalline rocks. In contrast, this project required in situ stress measurements to be taken in a relatively large-diameter borehole, drilled in weak sedimentary rocks by wireline drilling techniques, and consequently, significant adaptations to the installation equipment. The paper describes the adaption of the Borre Probe and its successful application in this project up to the end of 1992. Possible future applications of the technique are discussed.

Geotechnical Design and Instrumentation of an Anchored Cofferdam, Point Marion Lock, Pennsylvania

Point Marion Lock was designed to replace an existing navigation lock that has been in service on the Monongahela River near the Pennsylvania-West Virginia border for some 67 years. As a result of the close proximity of the planned excavation for the new lock, the land wall of the existing lock required extensive stabilization to permit it to be utilized as the river arm of the project cofferdam. Installation of 471 prestressed rock anchors was closely linked with each progressive stage of soil and rock excavation required to build the new lock. Adverse geologic conditions affected cofferdam stability in that the land wall of the existing operating lock was founded on weak sedimentary rocks exhibiting very low shear strength. Critical to the successful performance of the cofferdam was the design and installation of an extensive instrumentation program. A vast array of movement detection systems including inclinometers, alignment pins, shear strips, tilt plates and load cells were interfaced with both on-site and off-site computers to provide real-time monitoring of cofferdam performance throughout the excavation process. Data from instrumentation yielded invaluable information needed to make necessary adjustments in on-going construction activities including excavation and rock anchor installation.

Optical studies of cavity failure in weak sedimentary rocks : Fjaer, E; Bratli, R K; Malmo, J T; Okberg, L J; Holt, R M Proc 6th International Conference on Rock Mechanics, Montreal, 30 Aug–10 Sept 1987V2, P887–891. Publ Rotterdam: A A Balkema, 1987

Optical studies of cavity failure in weak sedimentary rocks : Fjaer, E; Bratli, R K; Malmo, J T; Okberg, L J; Holt, R M Proc 6th International Conference on Rock Mechanics, Montreal, 30 Aug–10 Sept 1987V2, P887–891. Publ Rotterdam: A A Balkema, 1987

Landslides and slope failures in Scotland: A review

Abstract Almost all documented landslides in Scotland belong to one of four categories: non‐rotational rock slope failures (major rockfalls, translational slides, topples or sags, often in some combination); rotational rock slope failures; debris flows; and translational slides in drift or regolith. Non‐rotational rock slope failures are particularly common on Highland metamorphic rocks, especially schists, and on igneous scarps in the Hebrides and Midland Valley; rotational rock slope failures almost invariably occur in weak sedimentary rocks overlain by resistant igneous rocks; and debris flows are most common on sandy drift or regolith. Former glacial activity has also been of importance in determining landslide distribution. The great majority of rock slope failures are ancient features, but debris flows and small translational slides in drift (both triggered mainly by intensive rainstorms) are much more frequent at present and cause much greater damage, particularly to communications.

Investigations for the Drakensberg Power Station complex in weak sedimentary rock

Investigations for the Drakensberg Power Station complex in weak sedimentary rock

Progress towards establishing relationships between the mineralogy and physical properties of coal measures rocks

The paper reaffirms both the applicability of standard X-ray diffraction techniques for the mineralogical analysis of argillaceous Coal Measures rocks and the use of such analyses in the assessment of physical properties of samples that can only be obtained from the field in a form unsuitable for normal uniaxial and triaxial compression testing procedures. Laboratory techniques which enable compression test samples to be prepared from weak sedimentary rocks are described, and results are presented for compression and swelling tests on samples of known mineralogy. Finally, the influence of mineralogy on compressive strength, cohesive strength and swelling is examined for a number of rocks.

Geology and Slope Stability in Western Pennsylvania

Western Pennsylvania has long been known for its landslide activity. This results from the geology and geologic history of the area. Flat lying interbedded strong and weak sedimentary rocks have been acted upon by erosion, stress relief, weathering, creep, and sliding processes to produce masses of marginally stable colluvial soil and rock on many of the steep hillsides that are common to the area. An observational engineering geology approach, supplemented and extended by concepts from soil and rock mechanics and other disciplines, has proven useful in dealing with colluvial slopes of Western Pennsylvania. Key elements of this approach, plus recommendations of practical value in dealing with colluvial slopes of western Pennsylvania, are presented. Each slope stability situation in western Pennsylvania (as elsewhere) is unique because of site specific geologic details. Therefore, in dealing with colluvial slopes, time and money can usually be better spent on understanding site geology and slope development processes than on soil and rock mechanics tests and analyses, though the latter may also be required.