Question

Please I need help to solve these problems

PROBLEMS 1. Figure 9.18 is representative of soil conditions at a construction site. If you are the con- tractor, select a dewatering method you would consider appropriate for each of the projects described below. Consider the information given in this chapter, earlier chapters and any be built and operated. Justify clearly any assumptions you make. Discuss what difficulties other information that may be appropriate. Describe in detail how your sy stem would you may encounter and how you should plan for them. A circular reservoir 100 ft in diameter is to be built with a bottom slab 25 ft below pre- sent ground surface. The groundwater level must be held at least 2 ft below the slab a. until the reservoir is filled. Standard penetretion resistance, Depth, Soil description 50 100 D some cobbles Loos to mediunm dense fine slity sand 50 Figure 9.18 Soil profile for Problem 1. Repeat Problem I for the following projects with soil conditions as indicated in Figure 9 a. b. c. 2. gure 9.19 1200 ft of an 18-in. sewer line is to be placed in a trench about 16 ft below A 30-ft-diameter concrete pump station is to be founded on the basalt rock at 65 ft in depth Conditions as in a, except that the pipeline is 28 ft below the ground surface. Standard penwtration resistance, Depth Soil description 50 100 Medium stiff to soft brown clayey silt 10 6/16172 Medium dee ilty fine sand 30 1t Medium dense slty clayey and 40 Stff to very stif gray clay 60 Basalit rock 70 100 50 Water content, w Figure 9.19 Soil profile for Problem 2.

Answer 1

Answer:

1.a)for the given construction conditions for circular reservoir and the soil conditions the dewatering methods may be followed are well point system and ejector system.

for the given condition of reservoir the required dewateing depth is about 9 ft.total depth of reservoir below the ground is 25 ft.the min depth of water level below the cap is 2 ft.the water level from the groung level is at arround 18 ft.then the rrrequirred depth of dewatering is 25+2-18 = 9ft.

for this depth of dewatering and the type of given sand and siltysoil the method of dewatering adopted is well point system and ejector systems.

but in this case we are adopting wellpoint system.the method includes porviding perforated pipes of metal or plastic of 5.0to12.0 cm dia whose bottom end is also perforated and connected to bottom of the water level which are rised above (rised pipes) and these are connected to the header pipe.the water from the bottom levelis rised throuh this header pipe and discharged by connecting these header pipe to the pumps.these pumps will discharge thewater from the pits and lowers the water level upto 30 ft in this method.

the main problems which involves in this method includes the stability of the slope and the blocking of the perforatedd pipes due to the debris.and the air is entered into the pipes through the joints of the pipe and it will reduce ethe pump effeciency.these entry of debris can be over come by providing screens at the bottom.and the entry of air can be limted by providing tight seal joints.

2)The strategies for dewatering utilized for the different activities are as per the following:

a) Wellpoint strategy for dewatering can be utilized for the case. This is on account of sewer line should be put at a profundity of 16ft subterranean level henceforth wellpoint technique would be adequate to make legitimate drawdown as this strategy is limited to make drawdown around 5 to 6 meters beneath the wellpoint pump level. Since the dirt layer experienced has low penetrability henceforth wellpoint strategy will be favored. Since the geologic conditions experienced likewise allow close separating of gadgets.

b) Deep well strategy for dewatering can be utilized as a part of this case. This is on account of the pump station is to be established on basalt shake which is 65ft profound and for the profound well technique the profundity of the wells could reach upto 30m.

c) Open sump directing technique for dewatering can be utilized as a part of this case. This is on account of the pipeline must be laid at 28ft subterranean surface in sandy soils.

The troubles that might be experienced and the means that could be taken to counter with the challenges are:

1) Creating profound well upto the level of basaltic shake might be troublesome.

The boring piece ought to be tipped with hard cutting material (Tungsten Carbide or mechanical precious stone) connected to the penetrate bar through a sledge system in the middle. Compacted air is utilized both for pivoting the bore bar and in addition creating a consistent pounding activity on the joined bore.

2) Installation of wellpoint framework could be minimal costly.

Supporting conditions should be enhanced to avert disappointment of the dewatering framework.

3) For profound well frameworks the measure of intensity required to work the pump couldn't be legitimately accessible in specific zones where access to powergrid isn't appropriate.

The alernative backup choice for power ought to be masterminded heretofore for the areas of profound well dewatering.