CivilAndEnvironmental Enginerring

  Geotextiles are geosynthetic products. While clothes are woven out of natural fibers such as cotton and silk , geotextiles are woven out of synthetic fibers. Synthetic fibers are manufactured using various polymers. Since geotextiles are woven , they are relatively porous. Geotextiles are used for the following purposes: Separation Filration Drainage Reinforcement Containmnent of contaminants Geomembranes Geomebranes are made of thin plastic sheets. They are much more impervious than geotextiles. For this reason, geomembranes have been used in the landful industry. Landfill liners, leachatte collection systems and landfill covers are made of geomembranes. Geosynthetic Clay Liners (GCLs) These are manufactured by sandwiching bentonite clay layer between two geotextiles or geomembranes. Geogrids , Geonet and Geocomposites Geogrids are mainy used for reinforcing purposes. The purposes of the geonets is to facilitate the drainage of

  Tunnel design is an interdisciplinary subject , involving geotechnical engineering , gelogy , geochemistry and hydrogeology. Tunnels are becoming increasingly common, due to newly available equipment such as tunnel boring machines , road headers , relatively safe blasting techniques and so on. Tunnel boring machines are widely used today due to their ability to construct tunnels at record speeds. The most important part of a tunnel boring machine is its cutter head. The cutter head is composed of a collectin of disc cutters that would be pressed into rocks. When the machine rotates, the disc cutters gradually cut the rock into pieces. Rock pieces that are cut are then collected in a bucket known as the muck bucket. Muck is removed from the tunnel by trains or the conveyor belt. The gripper , as the name indicates grips the tunnel sides so that the boring machine can be pushed hard into rock. Roadheaders These are not as powerful as tunnel boring machines and can be use

  Nomeclature changes from sector to sector. Generally , rock bolts also known as rocj anchors are either nonstressed or prestressed. Non-prestressed anchors are also known as rock dowels. When there is a slight movement in the rcok mass , rock dowels get tensioned and provide a resisting force. Cable bolts are group of wires used to create cable. Cable bolts are used for high capacity appplications. Rock anchors are used for shallow foundations , retainging walls bridges and tunnels. The four basic types of rock anchors are: Mechanical rock anchors or rock bolts Grouted Resin nachors Rock dowels Application They are widely used in retainging walls when rock is close enough for the anchors to be used. Mechanical rock anchors The most common popular mechanical anchor system is expansion shell anchors . To use expansion shell anchors , a hole is drilled in the rock and the rock bolt assembly is inserted.. The movement of thr anchor expands the two w

  Very high load foundations , caissons and piles are carried down to the rock layer to increase the bearing capacity. Rock can provide a much higher bearing capacity than soil. Unweathered rock can have a bearing capacity in excess of 60 tsf. On the other hand , weathered rock orrocks subjected to chemical attack could be unsuitable for foundation use. When a rock is heated to avery high temperature , it melts and becomes lava. Then lava coming out from a volcano cools down and becomes rock. Ocassionally lava comes out of the earth during volcanic eruptions and cools down and becomes rock. This type of rock is known as igneous rock. Some of the common igneous rock are: Granite Diabase. Basalt. Diorite. Volcanic eruptions are not only the process of rock origin. Soil particles constantly deposit on lakes beds and on the ocean floor. Many million years later, these deposition solidify and convert into rock. Such rocks are called sedimentary rocks.

  There are many geotechnical engineering software packages available on the market. Shallow foundations SPT Foundation This program computes the bearing capacity of shallow foundations using the Tezaghi bearing capacity equation. The SPT blow countmin the soil is used to obtain the friction angle to be used in the Terzaghi bearing capacity equation. The program is capable of conducting the settlement of foundation as well. The average SPT( N ) value within the depth of influence below the footing is used for settlements computations. A portion of the program is available without charge. ABC Bearing Capacity Computation This can be used to solve bearing capacity problems with many layers of soil. The program can be used to solve rigid foundations resting on a cohesive-frictional soil mass that is loaded to failure by a central vertical force. The program provides option for the cohesion to vary linearly with depth. In reality, such situations may be rar

Once the geotechnical engineer has decide to use the piles, the next question is which piles. As we have seen earlier they are many types of piles available. Timber piles are cheap but very difficult to install in hard soil. Steel piles may not be good in marine environments , due to corrossion. Case 1: Granular soil with boulders underlain by medium stiff clay Timber piles are not suitable for this situation, due to existence of boulders in the upper layers. The obvious choice is to drive the piles all the way to the rock. The piles could be designed as end bearing piles. If the decision was taken to drive piles to the rock for the configuration in, H-piles will be ideal. Unlike timber piles or pipe piles, H-piles can go through boulders. On the other hand , the rock may be too far for the piles to be driven. If the rock is too deep for piles , a number of alternatives can be envisioned. Drive large diameter pipe piles and place them in medium stiff clay. Construct