I found a large number of  java_pid*.hprof files in the directory D:\Program Files (x86)\CA\SOI\jsw\bin in SOI manager server.

Each file arournd 8GB, this is filling up drive space. What could be the reason and How Could we remove these files?

This problem usually happen when the SOI manager ran out of memory it was allocated and its java process crashed because of that creating the dump .hprof.
Check the SOI manager log for messages below
INFO   | jvm 10   | java.lang.OutOfMemoryError: Java heap space
STATUS | wrapper  | The JVM has run out of memory.  Restarting JVM.

Release : 4.2

Component : Service Operations Insight (SOI) Manager

Look in to the \CA\SOI\jsw\conf\wrapper-jvm-64.conf and look at line "set.JAVA_MAXMEM_MB=" to see how much is SOI manager is allowed to use. Increase this value (in MB).

If the physical memory is low on the SOI manager then you'll have to increase it on the server itself first.

- You'll have to recycle SOI manager services if once you increase the memory setting for SOI manager. You also should do the following when recycling the SOI
- Stop all SOI services on the SOI manager
  Delete all files from
  \CA\SOI\jsw\bin\logs
  CA\SOI\apache-activemq\data\kahadb
  CA\SOI\tomcat\temp
- Start CA SOI Application, CA SOI MQ and CA SOI UCF Broker.
- Open SOI debug page from http://<SOI manager host name>:7090/sam/debug
Select Triage Tests and click "Run Tests", wait for the "server application startup" shows completed then start all other services.

If You are running base SOI 4.2, apply the latest maintenance regardless of the issue. Latest monthly maintenance can be found at the link here:
https://techdocs.broadcom.com/us/product-content/recommended-reading/technical-document-index/ca-service-operations-insight-solutions-and-patches.html