LARE Grading and Earthwork Flashcards

A geotechnical report indicates that a project requires 10,000 cubic yards of compacted fill. The native soil to be used for the fill has a swell factor of 20% when excavated and a shrinkage factor of 10% from its original bank state when compacted. To achieve the required 10,000 cubic yards of compacted fill, approximately how much native soil must be excavated?

Answer: 11,111 cubic yards

This calculation requires working backward from the final compacted volume to the initial bank volume. The shrinkage factor of 10% means the compacted volume is 90% of the original bank volume. To find the required bank volume, divide the compacted volume by (1 - shrinkage factor): 10,000 CY / (1 - 0.10) = 10,000 / 0.90 = 11,111.11 cubic yards. The swell factor applies to the volume change from bank to loose state and is not needed to answer this specific question.

A landscape architect is designing a large turf panel for a public park. To ensure positive surface drainage and prevent ponding after a rain event, what is the generally accepted MINIMUM slope that should be specified for the lawn area?

Answer: 2.0%

A 2% slope is the standard minimum recommendation for turf areas to ensure adequate surface water runoff without being so steep as to cause erosion or feel uncomfortable to users. A 1% slope is typically the minimum for paved surfaces, while 0.5% is too flat for turf and may result in puddles. A 3% slope, while effective for drainage, is steeper than necessary for a minimum and may be undesirable for certain recreational activities.

During a site visit to a project under construction, a landscape architect observes a newly built segmental retaining wall that is showing signs of bulging in the center. Which of the following is the MOST likely cause of this failure?

Answer: Poor drainage and hydrostatic pressure

The most common cause of retaining wall failure, especially bulging, is the buildup of hydrostatic pressure from water trapped in the soil behind the wall. This pressure exerts a significant outward force. Proper drainage systems, such as a gravel backfill zone and weep holes or a perforated pipe, are critical to relieve this pressure. While inadequate foundation or lack of reinforcement can also cause failure, hydrostatic pressure is the primary culprit for bulging.

A contractor is preparing to build a path on a slope with cohesive soil. The specifications require the subgrade to be compacted to 95% of the maximum dry density. Which laboratory test is used to establish the standard for this requirement?

Answer: Standard Proctor Test

The Standard Proctor Test (or Modified Proctor Test) is the laboratory method used to determine the optimum moisture content at which a specific soil type will reach its maximum dry density when compacted with a standard amount of energy. Field compaction efforts are then measured against this laboratory standard, specified as a percentage (e.g., 95%) of the maximum proctor density.

On a construction site, a large, steep soil stockpile needs to be stabilized for a period of several months through the rainy season before the material is used. Which of the following is the most appropriate and cost-effective TEMPORARY erosion control measure?

Answer: Installing erosion control blankets over the stockpile

Erosion control blankets are specifically designed for temporary stabilization. They are biodegradable mats that protect the soil surface from raindrop impact and runoff, holding the soil in place until permanent measures can be installed or the soil is used. Retaining walls, soil nailing, and shotcrete are more permanent, structural, and expensive solutions not typically used for temporary stockpile protection.

A grading plan is being developed for a new residential site. Which of the following documents is MOST critical for the landscape architect to consult to understand the subsurface soil types, bearing capacity, and groundwater levels?

Answer: Geotechnical Report

The Geotechnical Report is prepared by a geotechnical engineer and provides a detailed analysis of subsurface conditions based on soil borings and lab tests. It contains crucial information for grading design, including soil properties, load-bearing capacity, recommendations for foundation design, slope stability, and groundwater conditions. The other documents provide different, though also important, site information.