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Climatic effects on pore-water pressure, deformation and stress mobilization of a vegetated volcanic soil slope in Hong Kong
Published in Tatiana Rotonda, Manuela Cecconi, Francesco Silvestri, Paolo Tommasi, Volcanic Rocks and Soils, 2016
A pair of earth pressure cells (EPCs) was installed at 2 m depth in the central portion of the landslide body to monitor any changes of total horizontal stress. The two EPCs were installed perpendicular to each other so that one of them measured total horizontal stress in the down-slope direction (σD), while the other measured the stress in the cross-slope direction (σC). At the installation location, a 1 m × 1 m (in plan) trial pit was excavated to a depth of 2.5 m. At 2 m depth, a slot with a size similar to the width of each EPC was cut and the EPC was inserted into the slot. Inevitably, these procedures caused stress release around the slot and hence, the initial total horizontal stress recorded by each EPC was reduced to zero. Thus, subsequent reading represents change of horizontal stress with reference to the initial zero total stress. To provide better contact between each EPC and the surrounding soil, the gap between them was filled with cement bentonite grout. This allows any tensile force to be transmitted between each cell and the soil (Brackley & Sanders, 1992).
The investigation of structural defects
Published in Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann, Understanding Housing Defects, 2013
Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann
A trial pit can provide much basic information about the sub-soil, the depth and size of foundation, the ground just below the foundation, tree roots, water levels, broken drains, etc. Initial testing of the sub-soil may be carried out on a simple basis, e.g. squeezing a small sample in the hand to determine water content or driving a metal bar into the sub-soil to indicate its firmness/density. However, such tests can only provide crude/simple information and, generally, more sophisticated testing needs to be undertaken in a laboratory. Laboratory testing can determine soil type, bearing capacity, water content, organic content, chemical content, plasticity and other relevant information.
Site investigation
Published in David Chapman, Nicole Metje, Alfred Stärk, Introduction to Tunnel Construction, 2017
David Chapman, Nicole Metje, Alfred Stärk
The principal methods for obtaining samples/cores include trial pit excavations, percussive drilling, rotary drilling techniques and even trial tunnels. Trial pit excavations are used for relatively shallow investigations to a few metres but, depending on available space, can open up a relatively large area of the ground. Percussive boring (known as either cable percussion or shell and auger boring) is the most common technique in the United Kingdom for soft ground (soil/weak or weathered rock) as it is relatively cheap, simple, flexible and robust. Through suitable ground, it can be used down to 60 m. Figure 2.4a and b shows a typical cable percussion rig. As the name implies, the boring is conducted by continuously raising and dropping weighted hollow drilling tools which gradually penetrate the ground. Rotary drilling is used in rocks and can drill down to hundreds of metres, although smaller rigs are available for shallower investigations. Figure 2.4c shows an example of a rotary drilling rig. The standard approach in the United Kingdom is to use cable percussion boring to rockhead and, if required, the borehole is extended by rotary coring. However, some strata, for example, weathered rock, overconsolidated clay and most chalk, may be sampled by either cable percussion or rotary drilling methods. These days, there is a wide range of drilling rigs. For example, the dual mast rig shown in Figure 2.5 combines a number of features including rotary drilling (Figure 2.5a), percussion action for going through localised obstructions, as well as the ability to conduct in situ standard penetration tests (SPTs) (Figure 2.5b) (in situ tests are described later in this section).
Waste crushed rock stabilised lateritic soil and spent carbide blends as a road base material
Published in Geomechanics and Geoengineering, 2021
S. S. R. Gidigasu, K. A. Lawer, S. K. Y. Gawu, Endene Emmanuel
A typical Ghanaian lateritic soil was used in the present study and were collected from Ejisu-Donaso in the Kumasi area. The soil was developed from weathered granitic rocks that intruded the meta-sedimentary rocks of the Birimian System of Ghana (Kesse 1985). Disturbed samples were obtained from manually excavated trial pits using shovel and pickaxe. The trial pit dimension was 1.2 m - length by 0.15 m - width and 2.40 m deep. The basic geotechnical properties of the soil are listed in Table 1. The significant oxides of the lateritic soils formed from the Birimian granites of Ghana are reported elsewhere (Gawu and Gidigasu 2013). The grain size distribution of the soil is shown in Figure 1. The soil classifies as an intermediate-plasticity clay (CI) according to the Unified Soil Classification System (USCS).
Investigation of an unusual landslide at Sai Kung Sai Wan Road, Sai Kung, Hong Kong
Published in HKIE Transactions, 2018
Dominic O K Lo, Rachel H C Law, Roland C T Wai, Axel K L Ng, Steven J Williamson, Jason K S Lee, Y M Cheng
Vegetation clearance strips were carried out 60 m above the main scarp and 40 m adjacent to the east flank, covering most of the potential areas of further instability. Vegetation was cut down to expose the ground surface so that any distress, such as tension cracks or deformation manifested on the ground surface could be observed. At about 20 m above the main scarp, a 400 mm vertical step was found but with no apparent lateral movement and the exposed soil was weathered suggesting it to be a relict tension crack. A trial pit was excavated to a depth of 3 m to investigate the 400 mm vertical step. No evidence of any tension crack, disturbance or dilation could be observed in the exposed soil faces below the step. No significant signs of distress could be observed within the adjacent hillside areas. No rock outcrop was observed above the source area and no evidence of daylighting of the basal failure plane was observed outside the source area.