Vertical Inclinometers Research Articles

Controlling base movement of MSE walls using recycled plastic pins

Sliding failure of Mechanically Stabilized Earth (MSE) retaining walls is a common problem when the shearing resistance developed between the wall base and foundation soil is insufficient. Highway MSE wall base failures can cause significant maintenance, repair, and cost implications for the state department of transportation. Controlling base movement using Recycled Plastic Pins (RPP) can be a potentially cost-effective and sustainable solution. RPPs are primarily manufactured from recycled plastics and have been successfully used for stabilizing shallow slope failures. The objective of the current study is to demonstrate the effectiveness of using RPPs for increasing the sliding resistance of an MSE wall. Four field test sections were constructed, out of which three were reinforced with different combinations of RPP sizes and spacings, while one was left unreinforced as a control section. Regular performance monitoring of the test sections was conducted using vertical inclinometers along with earth pressure plates. More than a year of results indicated a 75–88% reduction in lateral displacement of the reinforced wall base when compared with the control section. Additionally, the lateral earth pressure on the wall facing was decreased by 55–72% in the reinforced sections compared to the control section.

Long-Term Performance of a Highway Embankment Built with Lightweight Aggregates

This paper presents the results from a field and numerical studies performed to understand the long-term performance of a bridge approach embankment designed with lightweight, expanded clay and shale (ECS) aggregates to mitigate the settlements on a soft soil foundation. The ECS aggregates and traditional select fill were used to build southern and northern approach embankments, respectively, for a bridge on State Highway 360 in Arlington, Texas. An extensive series of laboratory tests were conducted to obtain the engineering behavior of ECS and the select fill materials before the construction. These properties were then used in the finite element modeling to simulate the embankment sections to verify the long-term performance. The embankment sections were instrumented with vertical inclinometers to monitor the lateral movements for more than four years. This data was used to validate the numerical models with an acceptable amount of accuracy. Then a parametric study was conducted for varied heights of embankments, thicknesses of foundation soil and also compression/recompression indices of foundation soil to develop design charts. The numerical, as well as field data, indicate that there is a two-thirds reduction in settlement of the foundation soil with the use of the lightweight material. The pre-consolidation pressure and the overconsolidation ratios govern the settlement behavior of the foundation soil due to lightweight embankments. The design charts can be useful in either predicting the embankment settlements for a given ECS embankment configuration or determine the allowable height of the ECS embankment for a specified settlement value when constructing in similar foundation soil encountered in this study.

Monitoring, Back analysis and Redesign of a Deep excavation Retaining system in marl formation. Case history, Modelling and Interpretation

We present in this paper a case study of retaining system of a deep excavation in a marly material in Beirut. The retaining system was redesigned using a new set of mechanical parameter considered more realistic than the set issued from the site investigation study. The new values were issued from back analysis of displacements measurement performed in the same site. The horizontally deflection of the retaining system was measured using three vertical inclinometers. The experimentation results are simulated by numerical calculation using finite elements code.

Use of Lightweight ECS as a Fill Material to Control Approach Embankment Settlements

A research study was conducted to evaluate the use of light weight aggregate (LWA) material produced from the manufacturing of expanded clay and shale (ECS) for potential use as a roadway approach embankment material. The use of such LWAs is expected to reduce stresses on subgrade foundation, which in turn could lead to less or no approach settlements. The test site was constructed on the south end of a new bridge overpass on State Highway 360 in Arlington, Texas and a control section was constructed on the north end of the same bridge. In the control section, a low plastic borrow soil (normal fill) was used as an embankment fill material. This paper presents both laboratory and field evaluations of the utilization of both ECS material and conventional borrow soil as embankments fill material. Shear strength and consolidation tests were performed to evaluate strength and compressibility characteristics. The embankment section was instrumented with vertical inclinometers to monitor the fill movements due to field loading conditions. Pavement surface profiling of both ends of the bridge was also performed at regular time intervals. Numerical simulations of test sections were also attempted. Based on the data obtained from experimental, field monitoring and numerical studies, it can be mentioned that the utilization of ECS LWAs are efficient in minimizing the bridge approach embankment settlements and reduced bump problems at the entry and departure of the bridges.

FieldP–ycurves in weathered rock

In weathered and decomposed rock profiles, the lack of an acceptable analysis procedure for estimating lateral load–displacement response of drilled shafts is compounded by the unavailability of weathered material properties, including the material's lateral subgrade reaction modulus. Such deficiency often leads to the overdesign of the drilled shaft foundation. Six field tests were conducted on drilled shafts to investigate the shape and magnitude of P–y curves in weathered rock material at three locations in North Carolina. The tested shafts were instrumented using dial gages, strain gages, and continuous vertical inclinometers. The measured load versus deflection data are used to study the stiffness response of weathered rock. Measured lateral responses are compared with the results estimated based on a "weak rock" model and a stiff clay model. The comparison shows that Reese's weak rock model overestimated the resistances of the tested shafts while the stiff clay model consistently underestimated the measured shaft resistances. The measured and computed results are analyzed and discussed.Key words: drilled shaft, weathered rock P–y curve, subgrade modulus, ultimate resistances in weathered rock, verification tests.

Extending the Period of Data Retrieval for Vertical Inclinometers

Vertical inclinometers are effective tools for accurately measuring horizontal deformations in soil and identifying the location of sliding surfaces. One drawback of inclinometers is that they can tolerate only limited deformation before being destroyed due to excessive displacement. This is particularly true when the displacement occurs on a distinct plane, as is common in shale and other weathered soils formed from sedimentary rock. In this technical note, a method is introduced that can be used to extend the useful life of vertical inclinometers by allowing displacement data to be recorded even after the inclinometer has been severed in shear. The procedure can be used both during inclinometer installation when large displacements are anticipated beforehand, or in a previously installed inclinometer when displacements are approaching the limit at which the inclinometer casing is functional. A brief description and data from a project where the procedure was successfully used are included.

APPLICATION OF SOIL NAILS TO THE STABILITY OF MINE WASTE SLOPES

The traditional soil nailed structure incorporates grouted or driven nails, and a wire mesh reinforced shotcrete facing to increase the stability of a slope or wall. This paper describes the construction and monitoring of a full-scale demonstration of nailing to stabilize coal mine spoil. The purpose of the investigation is to evaluate the performance of nailed slopes in mine spoil using methods proven for the stabilization of soil walls and slopes. The site in eastern Tennessee is a 12 meter high slope of dumped fill, composed of weathered shale chips, sandstone, and coal. The slope was formed by {open_quotes}pre-regulatory{close_quotes} contour surface mining operations and served as a work bench during mining. The material varies in size from silt to boulders, and has a small amount of cohesion. Portions of the mine spoil slope have experienced slope instability and erosion which have hampered subsequent reclamation activities. Three different nail spacings and three different nail lengths were used in the design. The 12 meter high structure is instrumented to permit measurement of nail strain, and vertical inclinometer readings and survey measurements will be used for the detection of ground movement. The results of this study will aid in the development of design more » recommendations and construction guidelines for the application of soil nailing to stabilize mine spoil. « less